diff options
Diffstat (limited to 'mm/userfaultfd.c')
| -rw-r--r-- | mm/userfaultfd.c | 3402 |
1 files changed, 3087 insertions, 315 deletions
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 927086bb4a3c..74f04c323c50 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -2,7 +2,12 @@ /* * mm/userfaultfd.c * + * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> + * Copyright (C) 2008-2009 Red Hat, Inc. * Copyright (C) 2015 Red Hat, Inc. + * + * Some part derived from fs/eventfd.c (anon inode setup) and + * mm/ksm.c (mm hashing). */ #include <linux/mm.h> @@ -14,12 +19,74 @@ #include <linux/userfaultfd_k.h> #include <linux/mmu_notifier.h> #include <linux/hugetlb.h> -#include <linux/shmem_fs.h> +#include <linux/list.h> +#include <linux/sched/mm.h> +#include <linux/mm_inline.h> +#include <linux/poll.h> +#include <linux/slab.h> +#include <linux/seq_file.h> +#include <linux/bug.h> +#include <linux/anon_inodes.h> +#include <linux/syscalls.h> +#include <linux/miscdevice.h> +#include <linux/uio.h> +#include <linux/file.h> +#include <linux/cleanup.h> #include <asm/tlbflush.h> #include <asm/tlb.h> #include "internal.h" #include "swap.h" +struct mfill_state { + struct userfaultfd_ctx *ctx; + unsigned long src_start; + unsigned long dst_start; + unsigned long len; + uffd_flags_t flags; + + struct vm_area_struct *vma; + unsigned long src_addr; + unsigned long dst_addr; + pmd_t *pmd; +}; + +static bool anon_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags) +{ + /* anonymous memory does not support MINOR mode */ + if (vm_flags & VM_UFFD_MINOR) + return false; + return true; +} + +static struct folio *anon_alloc_folio(struct vm_area_struct *vma, + unsigned long addr) +{ + struct folio *folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, + addr); + + if (!folio) + return NULL; + + if (mem_cgroup_charge(folio, vma->vm_mm, GFP_KERNEL)) { + folio_put(folio); + return NULL; + } + + return folio; +} + +static const struct vm_uffd_ops anon_uffd_ops = { + .can_userfault = anon_can_userfault, + .alloc_folio = anon_alloc_folio, +}; + +static const struct vm_uffd_ops *vma_uffd_ops(struct vm_area_struct *vma) +{ + if (vma_is_anonymous(vma)) + return &anon_uffd_ops; + return vma->vm_ops->uffd_ops; +} + static __always_inline bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end) { @@ -143,6 +210,128 @@ static void uffd_mfill_unlock(struct vm_area_struct *vma) } #endif +static void mfill_put_vma(struct mfill_state *state) +{ + if (!state->vma) + return; + + up_read(&state->ctx->map_changing_lock); + uffd_mfill_unlock(state->vma); + state->vma = NULL; +} + +static int mfill_get_vma(struct mfill_state *state) +{ + struct userfaultfd_ctx *ctx = state->ctx; + uffd_flags_t flags = state->flags; + struct vm_area_struct *dst_vma; + const struct vm_uffd_ops *ops; + int err; + + /* + * Make sure the vma is not shared, that the dst range is + * both valid and fully within a single existing vma. + */ + dst_vma = uffd_mfill_lock(ctx->mm, state->dst_start, state->len); + if (IS_ERR(dst_vma)) + return PTR_ERR(dst_vma); + + /* + * If memory mappings are changing because of non-cooperative + * operation (e.g. mremap) running in parallel, bail out and + * request the user to retry later + */ + down_read(&ctx->map_changing_lock); + state->vma = dst_vma; + err = -EAGAIN; + if (atomic_read(&ctx->mmap_changing)) + goto out_unlock; + + err = -EINVAL; + + /* + * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but + * it will overwrite vm_ops, so vma_is_anonymous must return false. + */ + if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) && + dst_vma->vm_flags & VM_SHARED)) + goto out_unlock; + + /* + * validate 'mode' now that we know the dst_vma: don't allow + * a wrprotect copy if the userfaultfd didn't register as WP. + */ + if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP)) + goto out_unlock; + + if (is_vm_hugetlb_page(dst_vma)) + return 0; + + ops = vma_uffd_ops(dst_vma); + if (!ops) + goto out_unlock; + + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) && + !ops->get_folio_noalloc) + goto out_unlock; + + return 0; + +out_unlock: + mfill_put_vma(state); + return err; +} + +static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address) +{ + pgd_t *pgd; + p4d_t *p4d; + pud_t *pud; + + pgd = pgd_offset(mm, address); + p4d = p4d_alloc(mm, pgd, address); + if (!p4d) + return NULL; + pud = pud_alloc(mm, p4d, address); + if (!pud) + return NULL; + /* + * Note that we didn't run this because the pmd was + * missing, the *pmd may be already established and in + * turn it may also be a trans_huge_pmd. + */ + return pmd_alloc(mm, pud, address); +} + +static int mfill_establish_pmd(struct mfill_state *state) +{ + struct mm_struct *dst_mm = state->ctx->mm; + pmd_t *dst_pmd, dst_pmdval; + + dst_pmd = mm_alloc_pmd(dst_mm, state->dst_addr); + if (unlikely(!dst_pmd)) + return -ENOMEM; + + dst_pmdval = pmdp_get_lockless(dst_pmd); + if (unlikely(pmd_none(dst_pmdval)) && + unlikely(__pte_alloc(dst_mm, dst_pmd))) + return -ENOMEM; + + dst_pmdval = pmdp_get_lockless(dst_pmd); + /* + * If the dst_pmd is THP don't override it and just be strict. + * (This includes the case where the PMD used to be THP and + * changed back to none after __pte_alloc().) + */ + if (unlikely(!pmd_present(dst_pmdval) || pmd_leaf(dst_pmdval))) + return -EEXIST; + if (unlikely(pmd_bad(dst_pmdval))) + return -EFAULT; + + state->pmd = dst_pmd; + return 0; +} + /* Check if dst_addr is outside of file's size. Must be called with ptl held. */ static bool mfill_file_over_size(struct vm_area_struct *dst_vma, unsigned long dst_addr) @@ -165,10 +354,10 @@ static bool mfill_file_over_size(struct vm_area_struct *dst_vma, * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem * and anon, and for both shared and private VMAs. */ -int mfill_atomic_install_pte(pmd_t *dst_pmd, - struct vm_area_struct *dst_vma, - unsigned long dst_addr, struct page *page, - bool newly_allocated, uffd_flags_t flags) +static int mfill_atomic_install_pte(pmd_t *dst_pmd, + struct vm_area_struct *dst_vma, + unsigned long dst_addr, struct page *page, + uffd_flags_t flags) { int ret; struct mm_struct *dst_mm = dst_vma->vm_mm; @@ -187,7 +376,7 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd, if (writable) _dst_pte = pte_mkwrite(_dst_pte, dst_vma); if (flags & MFILL_ATOMIC_WP) - _dst_pte = pte_mkuffd_wp(_dst_pte); + _dst_pte = pte_mkuffd(_dst_pte); ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl); @@ -212,9 +401,6 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd, goto out_unlock; if (page_in_cache) { - /* Usually, cache pages are already added to LRU */ - if (newly_allocated) - folio_add_lru(folio); folio_add_file_rmap_pte(folio, page, dst_vma); } else { folio_add_new_anon_rmap(folio, dst_vma, dst_addr, RMAP_EXCLUSIVE); @@ -229,6 +415,9 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd, set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte); + if (page_in_cache) + folio_unlock(folio); + /* No need to invalidate - it was non-present before */ update_mmu_cache(dst_vma, dst_addr, dst_pte); ret = 0; @@ -238,58 +427,174 @@ out: return ret; } -static int mfill_atomic_pte_copy(pmd_t *dst_pmd, - struct vm_area_struct *dst_vma, - unsigned long dst_addr, - unsigned long src_addr, - uffd_flags_t flags, - struct folio **foliop) +static int mfill_copy_folio_locked(struct folio *folio, unsigned long src_addr) { void *kaddr; int ret; + + kaddr = kmap_local_folio(folio, 0); + /* + * The read mmap_lock is held here. Despite the + * mmap_lock being read recursive a deadlock is still + * possible if a writer has taken a lock. For example: + * + * process A thread 1 takes read lock on own mmap_lock + * process A thread 2 calls mmap, blocks taking write lock + * process B thread 1 takes page fault, read lock on own mmap lock + * process B thread 2 calls mmap, blocks taking write lock + * process A thread 1 blocks taking read lock on process B + * process B thread 1 blocks taking read lock on process A + * + * Disable page faults to prevent potential deadlock + * and retry the copy outside the mmap_lock. + */ + pagefault_disable(); + ret = copy_from_user(kaddr, (const void __user *) src_addr, + PAGE_SIZE); + pagefault_enable(); + kunmap_local(kaddr); + + if (ret) + return -EFAULT; + + flush_dcache_folio(folio); + return ret; +} + +#define MFILL_RETRY_STATE_VMA_FLAGS \ + append_vma_flags(__VMA_UFFD_FLAGS, VMA_SHARED_BIT) + +/* + * VMA state saved before dropping the locks in mfill_copy_folio_retry(). + * Used to detect VMA replacement or incompatible changes after reacquiring the + * locks. + */ +struct mfill_retry_state { + const struct vm_uffd_ops *ops; + struct file *file; + vma_flags_t flags; + pgoff_t pgoff; +}; + +static void mfill_retry_state_save(struct mfill_retry_state *s, + struct vm_area_struct *vma) +{ + s->flags = vma_flags_and_mask(&vma->flags, MFILL_RETRY_STATE_VMA_FLAGS); + s->ops = vma_uffd_ops(vma); + s->pgoff = vma_start_pgoff(vma); + + if (vma->vm_file) + s->file = get_file(vma->vm_file); +} + +static bool mfill_retry_state_changed(struct mfill_retry_state *state, + struct vm_area_struct *vma) +{ + vma_flags_t flags = vma_flags_and_mask(&vma->flags, + MFILL_RETRY_STATE_VMA_FLAGS); + + /* Have any UFFD flags (missing, WP, minor) changed? */ + if (!vma_flags_same_pair(&state->flags, &flags)) + return true; + + /* VMA type or effective uffd_ops changed while the lock was dropped */ + if (state->ops != vma_uffd_ops(vma)) + return true; + + /* VMA was anonymous before; changed only if it no longer is */ + if (!state->file) + return !vma_is_anonymous(vma); + + /* VMA was file backed, but file, inode or offset has changed */ + if (!vma->vm_file || vma->vm_file->f_inode != state->file->f_inode || + state->file != vma->vm_file || vma_start_pgoff(vma) != state->pgoff) + return true; + + return false; +} + +static void mfill_retry_state_put(struct mfill_retry_state *s) +{ + if (s->file) + fput(s->file); +} + +DEFINE_FREE(retry_put, struct mfill_retry_state *, + if (_T) mfill_retry_state_put(_T)); + +static int mfill_copy_folio_retry(struct mfill_state *mfill_state, + struct folio *folio) +{ + struct mfill_retry_state retry_state = { 0 }; + struct mfill_retry_state *for_free __free(retry_put) = &retry_state; + unsigned long src_addr = mfill_state->src_addr; + void *kaddr; + int err; + + mfill_retry_state_save(&retry_state, mfill_state->vma); + + /* retry copying with mm_lock dropped */ + mfill_put_vma(mfill_state); + + kaddr = kmap_local_folio(folio, 0); + err = copy_from_user(kaddr, (const void __user *) src_addr, PAGE_SIZE); + kunmap_local(kaddr); + if (unlikely(err)) + return -EFAULT; + + flush_dcache_folio(folio); + + /* reget VMA and PMD, they could change underneath us */ + err = mfill_get_vma(mfill_state); + if (err) + return err; + + if (mfill_retry_state_changed(&retry_state, mfill_state->vma)) + return -EAGAIN; + + err = mfill_establish_pmd(mfill_state); + if (err) + return err; + + return 0; +} + +static int __mfill_atomic_pte(struct mfill_state *state, + const struct vm_uffd_ops *ops) +{ + unsigned long dst_addr = state->dst_addr; + unsigned long src_addr = state->src_addr; + uffd_flags_t flags = state->flags; struct folio *folio; + int ret; - if (!*foliop) { - ret = -ENOMEM; - folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma, - dst_addr); - if (!folio) - goto out; + if (!ops) { + VM_WARN_ONCE(1, "UFFDIO_COPY for unsupported VMA"); + return -EOPNOTSUPP; + } + + folio = ops->alloc_folio(state->vma, state->dst_addr); + if (!folio) + return -ENOMEM; - kaddr = kmap_local_folio(folio, 0); + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) { + ret = mfill_copy_folio_locked(folio, src_addr); /* - * The read mmap_lock is held here. Despite the - * mmap_lock being read recursive a deadlock is still - * possible if a writer has taken a lock. For example: - * - * process A thread 1 takes read lock on own mmap_lock - * process A thread 2 calls mmap, blocks taking write lock - * process B thread 1 takes page fault, read lock on own mmap lock - * process B thread 2 calls mmap, blocks taking write lock - * process A thread 1 blocks taking read lock on process B - * process B thread 1 blocks taking read lock on process A - * - * Disable page faults to prevent potential deadlock - * and retry the copy outside the mmap_lock. + * Fallback to copy_from_user outside mmap_lock. + * If retry is successful, mfill_copy_folio_locked() returns + * with locks retaken by mfill_get_vma(). + * If there was an error, we must mfill_put_vma() anyway and it + * will take care of unlocking if needed. */ - pagefault_disable(); - ret = copy_from_user(kaddr, (const void __user *) src_addr, - PAGE_SIZE); - pagefault_enable(); - kunmap_local(kaddr); - - /* fallback to copy_from_user outside mmap_lock */ if (unlikely(ret)) { - ret = -ENOENT; - *foliop = folio; - /* don't free the page */ - goto out; + ret = mfill_copy_folio_retry(state, folio); + if (ret) + goto err_folio_put; } - - flush_dcache_folio(folio); + } else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) { + clear_user_highpage(&folio->page, state->dst_addr); } else { - folio = *foliop; - *foliop = NULL; + VM_WARN_ONCE(1, "Unknown UFFDIO operation, flags: %x", flags); } /* @@ -299,65 +604,67 @@ static int mfill_atomic_pte_copy(pmd_t *dst_pmd, */ __folio_mark_uptodate(folio); - ret = -ENOMEM; - if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL)) - goto out_release; + if (ops->filemap_add) { + ret = ops->filemap_add(folio, state->vma, state->dst_addr); + if (ret) + goto err_folio_put; + } - ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, - &folio->page, true, flags); + ret = mfill_atomic_install_pte(state->pmd, state->vma, dst_addr, + &folio->page, flags); if (ret) - goto out_release; -out: - return ret; -out_release: + goto err_filemap_remove; + + return 0; + +err_filemap_remove: + if (ops->filemap_remove) + ops->filemap_remove(folio, state->vma); +err_folio_put: folio_put(folio); - goto out; + return ret; } -static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd, - struct vm_area_struct *dst_vma, - unsigned long dst_addr) +static int mfill_atomic_pte_copy(struct mfill_state *state) { - struct folio *folio; - int ret = -ENOMEM; - - folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr); - if (!folio) - return ret; - - if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL)) - goto out_put; + const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma); /* - * The memory barrier inside __folio_mark_uptodate makes sure that - * zeroing out the folio become visible before mapping the page - * using set_pte_at(). See do_anonymous_page(). + * The normal page fault path for a MAP_PRIVATE mapping in a + * file-backed VMA will invoke the fault, fill the hole in the file and + * COW it right away. The result generates plain anonymous memory. + * So when we are asked to fill a hole in a MAP_PRIVATE mapping, we'll + * generate anonymous memory directly without actually filling the + * hole. For the MAP_PRIVATE case the robustness check only happens in + * the pagetable (to verify it's still none) and not in the page cache. */ - __folio_mark_uptodate(folio); + if (!(state->vma->vm_flags & VM_SHARED)) + ops = &anon_uffd_ops; - ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, - &folio->page, true, 0); - if (ret) - goto out_put; + return __mfill_atomic_pte(state, ops); +} - return 0; -out_put: - folio_put(folio); - return ret; +static int mfill_atomic_pte_zeroed_folio(struct mfill_state *state) +{ + const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma); + + return __mfill_atomic_pte(state, ops); } -static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd, - struct vm_area_struct *dst_vma, - unsigned long dst_addr) +static int mfill_atomic_pte_zeropage(struct mfill_state *state) { + struct vm_area_struct *dst_vma = state->vma; + unsigned long dst_addr = state->dst_addr; + pmd_t *dst_pmd = state->pmd; pte_t _dst_pte, *dst_pte; spinlock_t *ptl; int ret; - if (mm_forbids_zeropage(dst_vma->vm_mm)) - return mfill_atomic_pte_zeroed_folio(dst_pmd, dst_vma, dst_addr); + if (mm_forbids_zeropage(dst_vma->vm_mm) || + (dst_vma->vm_flags & VM_SHARED)) + return mfill_atomic_pte_zeroed_folio(state); - _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr), + _dst_pte = pte_mkspecial(pfn_pte(zero_pfn(dst_addr), dst_vma->vm_page_prot)); ret = -EAGAIN; dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl); @@ -381,28 +688,29 @@ out: } /* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */ -static int mfill_atomic_pte_continue(pmd_t *dst_pmd, - struct vm_area_struct *dst_vma, - unsigned long dst_addr, - uffd_flags_t flags) +static int mfill_atomic_pte_continue(struct mfill_state *state) { - struct inode *inode = file_inode(dst_vma->vm_file); + struct vm_area_struct *dst_vma = state->vma; + const struct vm_uffd_ops *ops = vma_uffd_ops(dst_vma); + unsigned long dst_addr = state->dst_addr; pgoff_t pgoff = linear_page_index(dst_vma, dst_addr); + struct inode *inode = file_inode(dst_vma->vm_file); + uffd_flags_t flags = state->flags; + pmd_t *dst_pmd = state->pmd; struct folio *folio; struct page *page; int ret; - ret = shmem_get_folio(inode, pgoff, 0, &folio, SGP_NOALLOC); - /* Our caller expects us to return -EFAULT if we failed to find folio */ - if (ret == -ENOENT) - ret = -EFAULT; - if (ret) - goto out; - if (!folio) { - ret = -EFAULT; - goto out; + if (!ops) { + VM_WARN_ONCE(1, "UFFDIO_CONTINUE for unsupported VMA"); + return -EOPNOTSUPP; } + folio = ops->get_folio_noalloc(inode, pgoff); + /* Our caller expects us to return -EFAULT if we failed to find folio */ + if (IS_ERR_OR_NULL(folio)) + return -EFAULT; + page = folio_file_page(folio, pgoff); if (PageHWPoison(page)) { ret = -EIO; @@ -410,30 +718,28 @@ static int mfill_atomic_pte_continue(pmd_t *dst_pmd, } ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, - page, false, flags); + page, flags); if (ret) goto out_release; - folio_unlock(folio); - ret = 0; -out: - return ret; + return 0; + out_release: folio_unlock(folio); folio_put(folio); - goto out; + return ret; } /* Handles UFFDIO_POISON for all non-hugetlb VMAs. */ -static int mfill_atomic_pte_poison(pmd_t *dst_pmd, - struct vm_area_struct *dst_vma, - unsigned long dst_addr, - uffd_flags_t flags) +static int mfill_atomic_pte_poison(struct mfill_state *state) { - int ret; + struct vm_area_struct *dst_vma = state->vma; struct mm_struct *dst_mm = dst_vma->vm_mm; + unsigned long dst_addr = state->dst_addr; + pmd_t *dst_pmd = state->pmd; pte_t _dst_pte, *dst_pte; spinlock_t *ptl; + int ret; _dst_pte = make_pte_marker(PTE_MARKER_POISONED); ret = -EAGAIN; @@ -462,27 +768,6 @@ out: return ret; } -static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address) -{ - pgd_t *pgd; - p4d_t *p4d; - pud_t *pud; - - pgd = pgd_offset(mm, address); - p4d = p4d_alloc(mm, pgd, address); - if (!p4d) - return NULL; - pud = pud_alloc(mm, p4d, address); - if (!pud) - return NULL; - /* - * Note that we didn't run this because the pmd was - * missing, the *pmd may be already established and in - * turn it may also be a trans_huge_pmd. - */ - return pmd_alloc(mm, pud, address); -} - #ifdef CONFIG_HUGETLB_PAGE /* * mfill_atomic processing for HUGETLB vmas. Note that this routine is @@ -573,7 +858,7 @@ retry: * in the case of shared pmds. fault mutex prevents * races with other faulting threads. */ - idx = linear_page_index(dst_vma, dst_addr); + idx = hugetlb_linear_page_index(dst_vma, dst_addr); mapping = dst_vma->vm_file->f_mapping; hash = hugetlb_fault_mutex_hash(mapping, idx); mutex_lock(&hugetlb_fault_mutex_table[hash]); @@ -657,48 +942,21 @@ extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx, uffd_flags_t flags); #endif /* CONFIG_HUGETLB_PAGE */ -static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd, - struct vm_area_struct *dst_vma, - unsigned long dst_addr, - unsigned long src_addr, - uffd_flags_t flags, - struct folio **foliop) +static __always_inline ssize_t mfill_atomic_pte(struct mfill_state *state) { - ssize_t err; - - if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) { - return mfill_atomic_pte_continue(dst_pmd, dst_vma, - dst_addr, flags); - } else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) { - return mfill_atomic_pte_poison(dst_pmd, dst_vma, - dst_addr, flags); - } - - /* - * The normal page fault path for a shmem will invoke the - * fault, fill the hole in the file and COW it right away. The - * result generates plain anonymous memory. So when we are - * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll - * generate anonymous memory directly without actually filling - * the hole. For the MAP_PRIVATE case the robustness check - * only happens in the pagetable (to verify it's still none) - * and not in the radix tree. - */ - if (!(dst_vma->vm_flags & VM_SHARED)) { - if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) - err = mfill_atomic_pte_copy(dst_pmd, dst_vma, - dst_addr, src_addr, - flags, foliop); - else - err = mfill_atomic_pte_zeropage(dst_pmd, - dst_vma, dst_addr); - } else { - err = shmem_mfill_atomic_pte(dst_pmd, dst_vma, - dst_addr, src_addr, - flags, foliop); - } - - return err; + uffd_flags_t flags = state->flags; + + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) + return mfill_atomic_pte_continue(state); + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) + return mfill_atomic_pte_poison(state); + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY)) + return mfill_atomic_pte_copy(state); + if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) + return mfill_atomic_pte_zeropage(state); + + VM_WARN_ONCE(1, "Unknown UFFDIO operation, flags: %x", flags); + return -EOPNOTSUPP; } static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, @@ -707,13 +965,17 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, unsigned long len, uffd_flags_t flags) { - struct mm_struct *dst_mm = ctx->mm; - struct vm_area_struct *dst_vma; + struct mfill_state state = (struct mfill_state){ + .ctx = ctx, + .dst_start = dst_start, + .src_start = src_start, + .flags = flags, + .len = len, + .src_addr = src_start, + .dst_addr = dst_start, + }; + long copied = 0; ssize_t err; - pmd_t *dst_pmd; - unsigned long src_addr, dst_addr; - long copied; - struct folio *folio; /* * Sanitize the command parameters: @@ -725,125 +987,35 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx, VM_WARN_ON_ONCE(src_start + len <= src_start); VM_WARN_ON_ONCE(dst_start + len <= dst_start); - src_addr = src_start; - dst_addr = dst_start; - copied = 0; - folio = NULL; -retry: - /* - * Make sure the vma is not shared, that the dst range is - * both valid and fully within a single existing vma. - */ - dst_vma = uffd_mfill_lock(dst_mm, dst_start, len); - if (IS_ERR(dst_vma)) { - err = PTR_ERR(dst_vma); + err = mfill_get_vma(&state); + if (err) goto out; - } - - /* - * If memory mappings are changing because of non-cooperative - * operation (e.g. mremap) running in parallel, bail out and - * request the user to retry later - */ - down_read(&ctx->map_changing_lock); - err = -EAGAIN; - if (atomic_read(&ctx->mmap_changing)) - goto out_unlock; - - err = -EINVAL; - /* - * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but - * it will overwrite vm_ops, so vma_is_anonymous must return false. - */ - if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) && - dst_vma->vm_flags & VM_SHARED)) - goto out_unlock; - - /* - * validate 'mode' now that we know the dst_vma: don't allow - * a wrprotect copy if the userfaultfd didn't register as WP. - */ - if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP)) - goto out_unlock; /* * If this is a HUGETLB vma, pass off to appropriate routine */ - if (is_vm_hugetlb_page(dst_vma)) - return mfill_atomic_hugetlb(ctx, dst_vma, dst_start, + if (is_vm_hugetlb_page(state.vma)) + return mfill_atomic_hugetlb(ctx, state.vma, dst_start, src_start, len, flags); - if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma)) - goto out_unlock; - if (!vma_is_shmem(dst_vma) && - uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) - goto out_unlock; - - while (src_addr < src_start + len) { - pmd_t dst_pmdval; - - VM_WARN_ON_ONCE(dst_addr >= dst_start + len); + while (state.src_addr < src_start + len) { + VM_WARN_ON_ONCE(state.dst_addr >= dst_start + len); - dst_pmd = mm_alloc_pmd(dst_mm, dst_addr); - if (unlikely(!dst_pmd)) { - err = -ENOMEM; + err = mfill_establish_pmd(&state); + if (err) break; - } - dst_pmdval = pmdp_get_lockless(dst_pmd); - if (unlikely(pmd_none(dst_pmdval)) && - unlikely(__pte_alloc(dst_mm, dst_pmd))) { - err = -ENOMEM; - break; - } - dst_pmdval = pmdp_get_lockless(dst_pmd); - /* - * If the dst_pmd is THP don't override it and just be strict. - * (This includes the case where the PMD used to be THP and - * changed back to none after __pte_alloc().) - */ - if (unlikely(!pmd_present(dst_pmdval) || - pmd_trans_huge(dst_pmdval))) { - err = -EEXIST; - break; - } - if (unlikely(pmd_bad(dst_pmdval))) { - err = -EFAULT; - break; - } /* * For shmem mappings, khugepaged is allowed to remove page * tables under us; pte_offset_map_lock() will deal with that. */ - err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr, - src_addr, flags, &folio); + err = mfill_atomic_pte(&state); cond_resched(); - if (unlikely(err == -ENOENT)) { - void *kaddr; - - up_read(&ctx->map_changing_lock); - uffd_mfill_unlock(dst_vma); - VM_WARN_ON_ONCE(!folio); - - kaddr = kmap_local_folio(folio, 0); - err = copy_from_user(kaddr, - (const void __user *) src_addr, - PAGE_SIZE); - kunmap_local(kaddr); - if (unlikely(err)) { - err = -EFAULT; - goto out; - } - flush_dcache_folio(folio); - goto retry; - } else - VM_WARN_ON_ONCE(folio); - if (!err) { - dst_addr += PAGE_SIZE; - src_addr += PAGE_SIZE; + state.dst_addr += PAGE_SIZE; + state.src_addr += PAGE_SIZE; copied += PAGE_SIZE; if (fatal_signal_pending(current)) @@ -853,19 +1025,15 @@ retry: break; } -out_unlock: - up_read(&ctx->map_changing_lock); - uffd_mfill_unlock(dst_vma); + mfill_put_vma(&state); out: - if (folio) - folio_put(folio); VM_WARN_ON_ONCE(copied < 0); VM_WARN_ON_ONCE(err > 0); VM_WARN_ON_ONCE(!copied && !err); return copied ? copied : err; } -ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start, +static ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, uffd_flags_t flags) { @@ -873,7 +1041,7 @@ ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start, uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY)); } -ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx, +static ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len) { @@ -881,7 +1049,7 @@ ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx, uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE)); } -ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start, +static ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, uffd_flags_t flags) { @@ -897,7 +1065,7 @@ ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start, uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE)); } -ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start, +static ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, uffd_flags_t flags) { return mfill_atomic(ctx, start, 0, len, @@ -933,7 +1101,7 @@ long uffd_wp_range(struct vm_area_struct *dst_vma, return ret; } -int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start, +static int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start, unsigned long len, bool enable_wp) { struct mm_struct *dst_mm = ctx->mm; @@ -996,6 +1164,75 @@ out_unlock: return err; } +int mrwprotect_range(struct userfaultfd_ctx *ctx, unsigned long start, + unsigned long len, bool enable_rwp) +{ + struct mm_struct *dst_mm = ctx->mm; + unsigned long end = start + len; + struct vm_area_struct *dst_vma; + unsigned int mm_cp_flags; + struct mmu_gather tlb; + bool found = false; + VMA_ITERATOR(vmi, dst_mm, start); + + VM_WARN_ON_ONCE(start & ~PAGE_MASK); + VM_WARN_ON_ONCE(len & ~PAGE_MASK); + VM_WARN_ON_ONCE(start + len <= start); + + guard(mmap_read_lock)(dst_mm); + guard(rwsem_read)(&ctx->map_changing_lock); + + if (atomic_read(&ctx->mmap_changing)) + return -EAGAIN; + + if (enable_rwp) + mm_cp_flags = MM_CP_UFFD_RWP; + else + mm_cp_flags = MM_CP_UFFD_RWP_RESOLVE; + + /* + * Pre-scan the range: validate every spanned VMA before applying + * any change_protection() so a partial failure cannot leave the + * process with only a prefix of the range re-protected. + */ + for_each_vma_range(vmi, dst_vma, end) { + if (!userfaultfd_rwp(dst_vma)) + return -ENOENT; + + if (is_vm_hugetlb_page(dst_vma)) { + unsigned long page_mask; + + page_mask = vma_kernel_pagesize(dst_vma) - 1; + if ((start & page_mask) || (len & page_mask)) + return -EINVAL; + } + found = true; + } + if (!found) + return -ENOENT; + + vma_iter_set(&vmi, start); + tlb_gather_mmu(&tlb, dst_mm); + for_each_vma_range(vmi, dst_vma, end) { + unsigned long vma_start = max(dst_vma->vm_start, start); + unsigned long vma_end = min(dst_vma->vm_end, end); + unsigned int flags = mm_cp_flags; + + /* + * On resolve, try to upgrade writability per-VMA -- + * MM_CP_TRY_CHANGE_WRITABLE WARNs in + * maybe_change_pte_writable() if the VMA is not VM_WRITE, + * and RWP can be registered on PROT_READ-only mappings. + */ + if (!enable_rwp && vma_wants_manual_pte_write_upgrade(dst_vma)) + flags |= MM_CP_TRY_CHANGE_WRITABLE; + + change_protection(&tlb, dst_vma, vma_start, vma_end, flags); + } + tlb_finish_mmu(&tlb); + + return 0; +} void double_pt_lock(spinlock_t *ptl1, spinlock_t *ptl2) @@ -1115,7 +1352,7 @@ static long move_present_ptes(struct mm_struct *mm, } folio_move_anon_rmap(src_folio, dst_vma); - src_folio->index = linear_page_index(dst_vma, dst_addr); + src_folio->index = linear_anon_page_index(dst_vma, dst_addr); orig_dst_pte = folio_mk_pte(src_folio, dst_vma->vm_page_prot); /* Set soft dirty bit so userspace can notice the pte was moved */ @@ -1124,6 +1361,13 @@ static long move_present_ptes(struct mm_struct *mm, if (pte_dirty(orig_src_pte)) orig_dst_pte = pte_mkdirty(orig_dst_pte); orig_dst_pte = pte_mkwrite(orig_dst_pte, dst_vma); + + /* Re-arm RWP on the moved PTE if dst_vma is RWP-registered. */ + if (userfaultfd_rwp(dst_vma)) { + orig_dst_pte = pte_modify(orig_dst_pte, PAGE_NONE); + orig_dst_pte = pte_mkuffd(orig_dst_pte); + } + set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte); src_addr += PAGE_SIZE; @@ -1184,7 +1428,7 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, */ if (src_folio) { folio_move_anon_rmap(src_folio, dst_vma); - src_folio->index = linear_page_index(dst_vma, dst_addr); + src_folio->index = linear_anon_page_index(dst_vma, dst_addr); } else { /* * Check if the swap entry is cached after acquiring the src_pte @@ -1205,6 +1449,9 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte); if (pgtable_supports_soft_dirty()) orig_src_pte = pte_swp_mksoft_dirty(orig_src_pte); + /* Re-arm RWP on the moved swap entry if dst_vma is RWP-registered. */ + if (userfaultfd_rwp(dst_vma)) + orig_src_pte = pte_swp_mkuffd(orig_src_pte); set_pte_at(mm, dst_addr, dst_pte, orig_src_pte); double_pt_unlock(dst_ptl, src_ptl); @@ -1229,8 +1476,15 @@ static int move_zeropage_pte(struct mm_struct *mm, return -EAGAIN; } - zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr), + zero_pte = pte_mkspecial(pfn_pte(zero_pfn(dst_addr), dst_vma->vm_page_prot)); + + /* Re-arm RWP on the moved PTE if dst_vma is RWP-registered. */ + if (userfaultfd_rwp(dst_vma)) { + zero_pte = pte_modify(zero_pte, PAGE_NONE); + zero_pte = pte_mkuffd(zero_pte); + } + ptep_clear_flush(src_vma, src_addr, src_pte); set_pte_at(mm, dst_addr, dst_pte, zero_pte); double_pt_unlock(dst_ptl, src_ptl); @@ -1763,7 +2017,7 @@ static void uffd_move_unlock(struct vm_area_struct *dst_vma, * in the regions or not, but preventing the risk of having to split * the hugepmd during the remap. */ -ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, +static ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, unsigned long src_start, unsigned long len, __u64 mode) { struct mm_struct *mm = ctx->mm; @@ -1917,8 +2171,10 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, } if (err) { - if (err == -EAGAIN) + if (err == -EAGAIN) { + err = 0; continue; + } break; } @@ -1938,6 +2194,41 @@ out: return moved ? moved : err; } +static bool vma_can_userfault(struct vm_area_struct *vma, vm_flags_t vm_flags, + bool wp_async) +{ + const struct vm_uffd_ops *ops = vma_uffd_ops(vma); + + if (vma->vm_flags & (VM_DROPPABLE | VM_SHADOW_STACK)) + return false; + + if (!is_vm_hugetlb_page(vma) && (vma->vm_flags & VM_SPECIAL)) + return false; + + vm_flags &= __VM_UFFD_FLAGS; + + /* + * If WP is the only mode enabled and context is wp async, allow any + * memory type. + */ + if (wp_async && (vm_flags == VM_UFFD_WP)) + return true; + + /* For any other mode reject VMAs that don't implement vm_uffd_ops */ + if (!ops) + return false; + + /* + * If user requested uffd-wp but not enabled pte markers for + * uffd-wp, then only anonymous memory is supported + */ + if (!uffd_supports_wp_marker() && (vm_flags & VM_UFFD_WP) && + !vma_is_anonymous(vma)) + return false; + + return ops->can_userfault(vma, vm_flags); +} + static void userfaultfd_set_vm_flags(struct vm_area_struct *vma, vm_flags_t vm_flags) { @@ -1963,12 +2254,12 @@ static void userfaultfd_set_ctx(struct vm_area_struct *vma, (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags); } -void userfaultfd_reset_ctx(struct vm_area_struct *vma) +static void userfaultfd_reset_ctx(struct vm_area_struct *vma) { userfaultfd_set_ctx(vma, NULL, 0); } -struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, +static struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, struct vm_area_struct *prev, struct vm_area_struct *vma, unsigned long start, @@ -1976,6 +2267,9 @@ struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, { struct vm_area_struct *ret; bool give_up_on_oom = false; + vma_flags_t new_vma_flags = vma->flags; + + vma_flags_clear_mask(&new_vma_flags, __VMA_UFFD_FLAGS); /* * If we are modifying only and not splitting, just give up on the merge @@ -1984,13 +2278,26 @@ struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, if (start == vma->vm_start && end == vma->vm_end) give_up_on_oom = true; - /* Reset ptes for the whole vma range if wr-protected */ - if (userfaultfd_wp(vma)) - uffd_wp_range(vma, start, end - start, false); + /* Clear the uffd bit and/or restore protnone PTEs */ + if (userfaultfd_protected(vma)) { + unsigned int mm_cp_flags = 0; + struct mmu_gather tlb; + + if (userfaultfd_wp(vma)) + mm_cp_flags |= MM_CP_UFFD_WP_RESOLVE; + if (userfaultfd_rwp(vma)) + mm_cp_flags |= MM_CP_UFFD_RWP_RESOLVE; + if (vma_wants_manual_pte_write_upgrade(vma)) + mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE; + + tlb_gather_mmu(&tlb, vma->vm_mm); + change_protection(&tlb, vma, start, end, mm_cp_flags); + tlb_finish_mmu(&tlb); + } ret = vma_modify_flags_uffd(vmi, prev, vma, start, end, - vma->vm_flags & ~__VM_UFFD_FLAGS, - NULL_VM_UFFD_CTX, give_up_on_oom); + &new_vma_flags, NULL_VM_UFFD_CTX, + give_up_on_oom); /* * In the vma_merge() successful mprotect-like case 8: @@ -2004,16 +2311,17 @@ struct vm_area_struct *userfaultfd_clear_vma(struct vma_iterator *vmi, } /* Assumes mmap write lock taken, and mm_struct pinned. */ -int userfaultfd_register_range(struct userfaultfd_ctx *ctx, +static int userfaultfd_register_range(struct userfaultfd_ctx *ctx, struct vm_area_struct *vma, vm_flags_t vm_flags, unsigned long start, unsigned long end, bool wp_async) { + vma_flags_t vma_flags = legacy_to_vma_flags(vm_flags); VMA_ITERATOR(vmi, ctx->mm, start); struct vm_area_struct *prev = vma_prev(&vmi); unsigned long vma_end; - vm_flags_t new_flags; + vma_flags_t new_vma_flags; if (vma->vm_start < start) prev = vma; @@ -2024,23 +2332,34 @@ int userfaultfd_register_range(struct userfaultfd_ctx *ctx, VM_WARN_ON_ONCE(!vma_can_userfault(vma, vm_flags, wp_async)); VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx && vma->vm_userfaultfd_ctx.ctx != ctx); - VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE)); + VM_WARN_ON_ONCE(!vma_test(vma, VMA_MAYWRITE_BIT)); /* * Nothing to do: this vma is already registered into this * userfaultfd and with the right tracking mode too. */ if (vma->vm_userfaultfd_ctx.ctx == ctx && - (vma->vm_flags & vm_flags) == vm_flags) + vma_test_all_mask(vma, vma_flags)) goto skip; + /* + * Pre-scan in userfaultfd_register() already rejected mode + * switches that would drop VM_UFFD_WP or VM_UFFD_RWP, so a + * stray bit here is a bug. + */ + VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx == ctx && + vma->vm_flags & (VM_UFFD_WP | VM_UFFD_RWP) & ~vm_flags); + if (vma->vm_start > start) start = vma->vm_start; vma_end = min(end, vma->vm_end); - new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags; + new_vma_flags = vma->flags; + vma_flags_clear_mask(&new_vma_flags, __VMA_UFFD_FLAGS); + vma_flags_set_mask(&new_vma_flags, vma_flags); + vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end, - new_flags, + &new_vma_flags, (struct vm_userfaultfd_ctx){ctx}, /* give_up_on_oom = */false); if (IS_ERR(vma)) @@ -2064,7 +2383,7 @@ skip: return 0; } -void userfaultfd_release_new(struct userfaultfd_ctx *ctx) +static void userfaultfd_release_new(struct userfaultfd_ctx *ctx) { struct mm_struct *mm = ctx->mm; struct vm_area_struct *vma; @@ -2079,7 +2398,7 @@ void userfaultfd_release_new(struct userfaultfd_ctx *ctx) mmap_write_unlock(mm); } -void userfaultfd_release_all(struct mm_struct *mm, +static void userfaultfd_release_all(struct mm_struct *mm, struct userfaultfd_ctx *ctx) { struct vm_area_struct *vma, *prev; @@ -2114,3 +2433,2456 @@ void userfaultfd_release_all(struct mm_struct *mm, mmap_write_unlock(mm); mmput(mm); } + +static int sysctl_unprivileged_userfaultfd __read_mostly; + +#ifdef CONFIG_SYSCTL +static const struct ctl_table vm_userfaultfd_table[] = { + { + .procname = "unprivileged_userfaultfd", + .data = &sysctl_unprivileged_userfaultfd, + .maxlen = sizeof(sysctl_unprivileged_userfaultfd), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + .extra2 = SYSCTL_ONE, + }, +}; +#endif + +static struct kmem_cache *userfaultfd_ctx_cachep __ro_after_init; + +struct userfaultfd_fork_ctx { + struct userfaultfd_ctx *orig; + struct userfaultfd_ctx *new; + struct list_head list; +}; + +struct userfaultfd_unmap_ctx { + struct userfaultfd_ctx *ctx; + unsigned long start; + unsigned long end; + struct list_head list; +}; + +struct userfaultfd_wait_queue { + struct uffd_msg msg; + wait_queue_entry_t wq; + struct userfaultfd_ctx *ctx; + bool waken; +}; + +struct userfaultfd_wake_range { + unsigned long start; + unsigned long len; +}; + +/* internal indication that UFFD_API ioctl was successfully executed */ +#define UFFD_FEATURE_INITIALIZED (1u << 31) + +/* + * UFFDIO_SET_MODE updates ctx->features under mmap_write_lock with + * WRITE_ONCE; readers that run outside mmap_read_lock or the per-VMA + * lock (poll/read_iter/ioctl, fdinfo) must pair with READ_ONCE. + */ +static unsigned int userfaultfd_features(struct userfaultfd_ctx *ctx) +{ + return READ_ONCE(ctx->features); +} + +static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx) +{ + return userfaultfd_features(ctx) & UFFD_FEATURE_INITIALIZED; +} + +static bool userfaultfd_wp_async_ctx(struct userfaultfd_ctx *ctx) +{ + return ctx && (userfaultfd_features(ctx) & UFFD_FEATURE_WP_ASYNC); +} + +static bool userfaultfd_rwp_async_ctx(struct userfaultfd_ctx *ctx) +{ + return ctx && (userfaultfd_features(ctx) & UFFD_FEATURE_RWP_ASYNC); +} + +/* + * Whether WP_UNPOPULATED is enabled on the uffd context. It is only + * meaningful when userfaultfd_wp()==true on the vma and when it's + * anonymous. + */ +bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma) +{ + struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx; + + if (!ctx) + return false; + + return userfaultfd_features(ctx) & UFFD_FEATURE_WP_UNPOPULATED; +} + +static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode, + int wake_flags, void *key) +{ + struct userfaultfd_wake_range *range = key; + int ret; + struct userfaultfd_wait_queue *uwq; + unsigned long start, len; + + uwq = container_of(wq, struct userfaultfd_wait_queue, wq); + ret = 0; + /* len == 0 means wake all */ + start = range->start; + len = range->len; + if (len && (start > uwq->msg.arg.pagefault.address || + start + len <= uwq->msg.arg.pagefault.address)) + goto out; + WRITE_ONCE(uwq->waken, true); + /* + * The Program-Order guarantees provided by the scheduler + * ensure uwq->waken is visible before the task is woken. + */ + ret = wake_up_state(wq->private, mode); + if (ret) { + /* + * Wake only once, autoremove behavior. + * + * After the effect of list_del_init is visible to the other + * CPUs, the waitqueue may disappear from under us, see the + * !list_empty_careful() in handle_userfault(). + * + * try_to_wake_up() has an implicit smp_mb(), and the + * wq->private is read before calling the extern function + * "wake_up_state" (which in turns calls try_to_wake_up). + */ + list_del_init(&wq->entry); + } +out: + return ret; +} + +/** + * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd + * context. + * @ctx: [in] Pointer to the userfaultfd context. + */ +static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx) +{ + refcount_inc(&ctx->refcount); +} + +/** + * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd + * context. + * @ctx: [in] Pointer to userfaultfd context. + * + * The userfaultfd context reference must have been previously acquired either + * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget(). + */ +static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx) +{ + if (refcount_dec_and_test(&ctx->refcount)) { + VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_pending_wqh.lock)); + VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_pending_wqh)); + VM_WARN_ON_ONCE(spin_is_locked(&ctx->fault_wqh.lock)); + VM_WARN_ON_ONCE(waitqueue_active(&ctx->fault_wqh)); + VM_WARN_ON_ONCE(spin_is_locked(&ctx->event_wqh.lock)); + VM_WARN_ON_ONCE(waitqueue_active(&ctx->event_wqh)); + VM_WARN_ON_ONCE(spin_is_locked(&ctx->fd_wqh.lock)); + VM_WARN_ON_ONCE(waitqueue_active(&ctx->fd_wqh)); + mmdrop(ctx->mm); + kmem_cache_free(userfaultfd_ctx_cachep, ctx); + } +} + +static inline void msg_init(struct uffd_msg *msg) +{ + BUILD_BUG_ON(sizeof(struct uffd_msg) != 32); + /* + * Must use memset to zero out the paddings or kernel data is + * leaked to userland. + */ + memset(msg, 0, sizeof(struct uffd_msg)); +} + +static inline struct uffd_msg userfault_msg(unsigned long address, + unsigned long real_address, + unsigned int flags, + unsigned long reason, + unsigned int features) +{ + struct uffd_msg msg; + + msg_init(&msg); + msg.event = UFFD_EVENT_PAGEFAULT; + + msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ? + real_address : address; + + /* + * These flags indicate why the userfault occurred: + * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault. + * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault. + * - Neither of these flags being set indicates a MISSING fault. + * + * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write + * fault. Otherwise, it was a read fault. + */ + if (flags & FAULT_FLAG_WRITE) + msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE; + if (reason & VM_UFFD_WP) + msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP; + if (reason & VM_UFFD_RWP) + msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_RWP; + if (reason & VM_UFFD_MINOR) + msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR; + if (features & UFFD_FEATURE_THREAD_ID) + msg.arg.pagefault.feat.ptid = task_pid_vnr(current); + return msg; +} + +#ifdef CONFIG_HUGETLB_PAGE +/* + * Same functionality as userfaultfd_must_wait below with modifications for + * hugepmd ranges. + */ +static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, + struct vm_fault *vmf, + unsigned long reason) +{ + struct vm_area_struct *vma = vmf->vma; + pte_t *ptep, pte; + + assert_fault_locked(vmf); + + ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma)); + if (!ptep) + return true; + + pte = huge_ptep_get(vma->vm_mm, vmf->address, ptep); + + /* + * Lockless access: we're in a wait_event so it's ok if it + * changes under us. + */ + + /* Entry is still missing, wait for userspace to resolve the fault. */ + if (huge_pte_none(pte)) + return true; + /* UFFD PTE markers require userspace to resolve the fault. */ + if (pte_is_uffd_marker(pte)) + return true; + /* + * Concurrent migration may have replaced the present PTE with a + * non-marker swap entry between fault delivery and this lockless + * re-check. huge_pte_write() on a swap entry decodes random offset + * bits, so gate it on pte_present(). The migration completion path + * will re-deliver the fault if it still needs userspace. + */ + if (!pte_present(pte)) + return false; + /* + * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to + * resolve the fault. + */ + if (!huge_pte_write(pte) && (reason & VM_UFFD_WP)) + return true; + /* + * PTE is still RW-protected (protnone with uffd bit), wait for + * resolution. Plain PROT_NONE without the marker is not an RWP fault. + */ + if (pte_protnone(pte) && huge_pte_uffd(pte) && (reason & VM_UFFD_RWP)) + return true; + + return false; +} +#else +static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, + struct vm_fault *vmf, + unsigned long reason) +{ + /* Should never get here. */ + VM_WARN_ON_ONCE(1); + return false; +} +#endif /* CONFIG_HUGETLB_PAGE */ + +/* + * Verify the pagetables are still not ok after having registered into + * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any + * userfault that has already been resolved, if userfaultfd_read_iter and + * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different + * threads. + */ +static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx, + struct vm_fault *vmf, + unsigned long reason) +{ + struct mm_struct *mm = ctx->mm; + unsigned long address = vmf->address; + pgd_t *pgd; + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd, _pmd; + pte_t *pte; + pte_t ptent; + bool ret; + + assert_fault_locked(vmf); + + pgd = pgd_offset(mm, address); + if (!pgd_present(*pgd)) + return true; + p4d = p4d_offset(pgd, address); + if (!p4d_present(*p4d)) + return true; + pud = pud_offset(p4d, address); + if (!pud_present(*pud)) + return true; + pmd = pmd_offset(pud, address); +again: + _pmd = pmdp_get_lockless(pmd); + if (pmd_none(_pmd)) + return true; + + /* + * A race could arise which would result in a softleaf entry such as + * migration entry unexpectedly being present in the PMD, so explicitly + * check for this and bail out if so. + */ + if (!pmd_present(_pmd)) + return false; + + if (pmd_trans_huge(_pmd)) { + if (!pmd_write(_pmd) && (reason & VM_UFFD_WP)) + return true; + if (pmd_protnone(_pmd) && pmd_uffd(_pmd) && + (reason & VM_UFFD_RWP)) + return true; + return false; + } + + pte = pte_offset_map(pmd, address); + if (!pte) + goto again; + + /* + * Lockless access: we're in a wait_event so it's ok if it + * changes under us. + */ + ptent = ptep_get(pte); + + ret = true; + /* Entry is still missing, wait for userspace to resolve the fault. */ + if (pte_none(ptent)) + goto out; + /* UFFD PTE markers require userspace to resolve the fault. */ + if (pte_is_uffd_marker(ptent)) + goto out; + /* + * Concurrent swap-out / migration may have replaced the present PTE + * with a non-marker swap entry between fault delivery and this + * lockless re-check. pte_write() on a swap entry decodes random + * offset bits, so gate it on pte_present(). The page-in path will + * re-deliver the fault if it still needs userspace. + */ + if (!pte_present(ptent)) { + ret = false; + goto out; + } + /* + * If VMA has UFFD WP faults enabled and WP fault, wait for userspace to + * resolve the fault. + */ + if (!pte_write(ptent) && (reason & VM_UFFD_WP)) + goto out; + /* + * PTE is still RW-protected (protnone with uffd bit), wait for + * userspace to resolve. Plain PROT_NONE without the marker is not + * an RWP fault. + */ + if (pte_protnone(ptent) && pte_uffd(ptent) && (reason & VM_UFFD_RWP)) + goto out; + + ret = false; +out: + pte_unmap(pte); + return ret; +} + +static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags) +{ + if (flags & FAULT_FLAG_INTERRUPTIBLE) + return TASK_INTERRUPTIBLE; + + if (flags & FAULT_FLAG_KILLABLE) + return TASK_KILLABLE; + + return TASK_UNINTERRUPTIBLE; +} + +/* + * The locking rules involved in returning VM_FAULT_RETRY depending on + * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and + * FAULT_FLAG_KILLABLE are not straightforward. The "Caution" + * recommendation in __lock_page_or_retry is not an understatement. + * + * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released + * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is + * not set. + * + * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not + * set, VM_FAULT_RETRY can still be returned if and only if there are + * fatal_signal_pending()s, and the mmap_lock must be released before + * returning it. + */ +vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason) +{ + struct vm_area_struct *vma = vmf->vma; + struct mm_struct *mm = vma->vm_mm; + struct userfaultfd_ctx *ctx; + struct userfaultfd_wait_queue uwq; + vm_fault_t ret = VM_FAULT_SIGBUS; + bool must_wait; + unsigned int blocking_state; + + /* + * We don't do userfault handling for the final child pid update + * and when coredumping (faults triggered by get_dump_page()). + */ + if (current->flags & (PF_EXITING|PF_DUMPCORE)) + goto out; + + assert_fault_locked(vmf); + + ctx = vma->vm_userfaultfd_ctx.ctx; + if (!ctx) + goto out; + + VM_WARN_ON_ONCE(ctx->mm != mm); + + /* Any unrecognized flag is a bug. */ + VM_WARN_ON_ONCE(reason & ~__VM_UFFD_FLAGS); + /* 0 or > 1 flags set is a bug; we expect exactly 1. */ + VM_WARN_ON_ONCE(!reason || (reason & (reason - 1))); + + if (ctx->features & UFFD_FEATURE_SIGBUS) + goto out; + if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY)) + goto out; + + /* + * Check that we can return VM_FAULT_RETRY. + * + * NOTE: it should become possible to return VM_FAULT_RETRY + * even if FAULT_FLAG_TRIED is set without leading to gup() + * -EBUSY failures, if the userfaultfd is to be extended for + * VM_UFFD_WP tracking and we intend to arm the userfault + * without first stopping userland access to the memory. For + * VM_UFFD_MISSING userfaults this is enough for now. + */ + if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) { + /* + * Validate the invariant that nowait must allow retry + * to be sure not to return SIGBUS erroneously on + * nowait invocations. + */ + VM_WARN_ON_ONCE(vmf->flags & FAULT_FLAG_RETRY_NOWAIT); +#ifdef CONFIG_DEBUG_VM + if (printk_ratelimit()) { + pr_warn("FAULT_FLAG_ALLOW_RETRY missing %x\n", + vmf->flags); + dump_stack(); + } +#endif + goto out; + } + + /* + * Handle nowait, not much to do other than tell it to retry + * and wait. + */ + ret = VM_FAULT_RETRY; + if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) + goto out; + + if (unlikely(READ_ONCE(ctx->released))) { + /* + * If a concurrent release is detected, do not return + * VM_FAULT_SIGBUS or VM_FAULT_NOPAGE, but instead always + * return VM_FAULT_RETRY with lock released proactively. + * + * If we were to return VM_FAULT_SIGBUS here, the non + * cooperative manager would be instead forced to + * always call UFFDIO_UNREGISTER before it can safely + * close the uffd, to avoid involuntary SIGBUS triggered. + * + * If we were to return VM_FAULT_NOPAGE, it would work for + * the fault path, in which the lock will be released + * later. However for GUP, faultin_page() does nothing + * special on NOPAGE, so GUP would spin retrying without + * releasing the mmap read lock, causing possible livelock. + * + * Here only VM_FAULT_RETRY would make sure the mmap lock + * be released immediately, so that the thread concurrently + * releasing the userfault would always make progress. + */ + release_fault_lock(vmf); + goto out; + } + + /* take the reference before dropping the mmap_lock */ + userfaultfd_ctx_get(ctx); + + init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); + uwq.wq.private = current; + uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags, + reason, ctx->features); + uwq.ctx = ctx; + uwq.waken = false; + + blocking_state = userfaultfd_get_blocking_state(vmf->flags); + + /* + * Take the vma lock now, in order to safely call + * userfaultfd_huge_must_wait() later. Since acquiring the + * (sleepable) vma lock can modify the current task state, that + * must be before explicitly calling set_current_state(). + */ + if (is_vm_hugetlb_page(vma)) + hugetlb_vma_lock_read(vma); + + spin_lock_irq(&ctx->fault_pending_wqh.lock); + /* + * After the __add_wait_queue the uwq is visible to userland + * through poll/read(). + */ + __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq); + /* + * The smp_mb() after __set_current_state prevents the reads + * following the spin_unlock to happen before the list_add in + * __add_wait_queue. + */ + set_current_state(blocking_state); + spin_unlock_irq(&ctx->fault_pending_wqh.lock); + + if (is_vm_hugetlb_page(vma)) { + must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason); + hugetlb_vma_unlock_read(vma); + } else { + must_wait = userfaultfd_must_wait(ctx, vmf, reason); + } + + release_fault_lock(vmf); + + if (likely(must_wait && !READ_ONCE(ctx->released))) { + wake_up_poll(&ctx->fd_wqh, EPOLLIN); + schedule(); + } + + __set_current_state(TASK_RUNNING); + + /* + * Here we race with the list_del; list_add in + * userfaultfd_ctx_read(), however because we don't ever run + * list_del_init() to refile across the two lists, the prev + * and next pointers will never point to self. list_add also + * would never let any of the two pointers to point to + * self. So list_empty_careful won't risk to see both pointers + * pointing to self at any time during the list refile. The + * only case where list_del_init() is called is the full + * removal in the wake function and there we don't re-list_add + * and it's fine not to block on the spinlock. The uwq on this + * kernel stack can be released after the list_del_init. + */ + if (!list_empty_careful(&uwq.wq.entry)) { + spin_lock_irq(&ctx->fault_pending_wqh.lock); + /* + * No need of list_del_init(), the uwq on the stack + * will be freed shortly anyway. + */ + list_del(&uwq.wq.entry); + spin_unlock_irq(&ctx->fault_pending_wqh.lock); + } + + /* + * ctx may go away after this if the userfault pseudo fd is + * already released. + */ + userfaultfd_ctx_put(ctx); + +out: + return ret; +} + +static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx, + struct userfaultfd_wait_queue *ewq) +{ + struct userfaultfd_ctx *release_new_ctx; + + if (WARN_ON_ONCE(current->flags & PF_EXITING)) + goto out; + + ewq->ctx = ctx; + init_waitqueue_entry(&ewq->wq, current); + release_new_ctx = NULL; + + spin_lock_irq(&ctx->event_wqh.lock); + /* + * After the __add_wait_queue the uwq is visible to userland + * through poll/read(). + */ + __add_wait_queue(&ctx->event_wqh, &ewq->wq); + for (;;) { + set_current_state(TASK_KILLABLE); + if (ewq->msg.event == 0) + break; + if (READ_ONCE(ctx->released) || + fatal_signal_pending(current)) { + /* + * &ewq->wq may be queued in fork_event, but + * __remove_wait_queue ignores the head + * parameter. It would be a problem if it + * didn't. + */ + __remove_wait_queue(&ctx->event_wqh, &ewq->wq); + if (ewq->msg.event == UFFD_EVENT_FORK) { + struct userfaultfd_ctx *new; + + new = (struct userfaultfd_ctx *) + (unsigned long) + ewq->msg.arg.reserved.reserved1; + release_new_ctx = new; + } + break; + } + + spin_unlock_irq(&ctx->event_wqh.lock); + + wake_up_poll(&ctx->fd_wqh, EPOLLIN); + schedule(); + + spin_lock_irq(&ctx->event_wqh.lock); + } + __set_current_state(TASK_RUNNING); + spin_unlock_irq(&ctx->event_wqh.lock); + + if (release_new_ctx) { + userfaultfd_release_new(release_new_ctx); + userfaultfd_ctx_put(release_new_ctx); + } + + /* + * ctx may go away after this if the userfault pseudo fd is + * already released. + */ +out: + atomic_dec(&ctx->mmap_changing); + VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0); + userfaultfd_ctx_put(ctx); +} + +static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx, + struct userfaultfd_wait_queue *ewq) +{ + ewq->msg.event = 0; + wake_up_locked(&ctx->event_wqh); + __remove_wait_queue(&ctx->event_wqh, &ewq->wq); +} + +int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs) +{ + struct userfaultfd_ctx *ctx = NULL, *octx; + struct userfaultfd_fork_ctx *fctx; + + octx = vma->vm_userfaultfd_ctx.ctx; + if (!octx) + return 0; + + if (!(octx->features & UFFD_FEATURE_EVENT_FORK)) { + userfaultfd_reset_ctx(vma); + return 0; + } + + list_for_each_entry(fctx, fcs, list) + if (fctx->orig == octx) { + ctx = fctx->new; + break; + } + + if (!ctx) { + fctx = kmalloc_obj(*fctx); + if (!fctx) + return -ENOMEM; + + ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); + if (!ctx) { + kfree(fctx); + return -ENOMEM; + } + + refcount_set(&ctx->refcount, 1); + ctx->flags = octx->flags; + ctx->features = octx->features; + ctx->released = false; + init_rwsem(&ctx->map_changing_lock); + atomic_set(&ctx->mmap_changing, 0); + ctx->mm = vma->vm_mm; + mmgrab(ctx->mm); + + userfaultfd_ctx_get(octx); + down_write(&octx->map_changing_lock); + atomic_inc(&octx->mmap_changing); + up_write(&octx->map_changing_lock); + fctx->orig = octx; + fctx->new = ctx; + list_add_tail(&fctx->list, fcs); + } + + vma->vm_userfaultfd_ctx.ctx = ctx; + return 0; +} + +static void dup_fctx(struct userfaultfd_fork_ctx *fctx) +{ + struct userfaultfd_ctx *ctx = fctx->orig; + struct userfaultfd_wait_queue ewq; + + msg_init(&ewq.msg); + + ewq.msg.event = UFFD_EVENT_FORK; + ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new; + + userfaultfd_event_wait_completion(ctx, &ewq); +} + +void dup_userfaultfd_complete(struct list_head *fcs) +{ + struct userfaultfd_fork_ctx *fctx, *n; + + list_for_each_entry_safe(fctx, n, fcs, list) { + dup_fctx(fctx); + list_del(&fctx->list); + kfree(fctx); + } +} + +void dup_userfaultfd_fail(struct list_head *fcs) +{ + struct userfaultfd_fork_ctx *fctx, *n; + + /* + * An error has occurred on fork, we will tear memory down, but have + * allocated memory for fctx's and raised reference counts for both the + * original and child contexts (and on the mm for each as a result). + * + * These would ordinarily be taken care of by a user handling the event, + * but we are no longer doing so, so manually clean up here. + * + * mm tear down will take care of cleaning up VMA contexts. + */ + list_for_each_entry_safe(fctx, n, fcs, list) { + struct userfaultfd_ctx *octx = fctx->orig; + struct userfaultfd_ctx *ctx = fctx->new; + + atomic_dec(&octx->mmap_changing); + VM_WARN_ON_ONCE(atomic_read(&octx->mmap_changing) < 0); + userfaultfd_ctx_put(octx); + userfaultfd_ctx_put(ctx); + + list_del(&fctx->list); + kfree(fctx); + } +} + +void mremap_userfaultfd_prep(struct vm_area_struct *vma, + struct vm_userfaultfd_ctx *vm_ctx) +{ + struct userfaultfd_ctx *ctx; + + ctx = vma->vm_userfaultfd_ctx.ctx; + + if (!ctx) + return; + + if (ctx->features & UFFD_FEATURE_EVENT_REMAP) { + vm_ctx->ctx = ctx; + userfaultfd_ctx_get(ctx); + down_write(&ctx->map_changing_lock); + atomic_inc(&ctx->mmap_changing); + up_write(&ctx->map_changing_lock); + } else { + /* Drop uffd context if remap feature not enabled */ + userfaultfd_reset_ctx(vma); + } +} + +void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx, + unsigned long from, unsigned long to, + unsigned long len) +{ + struct userfaultfd_ctx *ctx = vm_ctx->ctx; + struct userfaultfd_wait_queue ewq; + + if (!ctx) + return; + + msg_init(&ewq.msg); + + ewq.msg.event = UFFD_EVENT_REMAP; + ewq.msg.arg.remap.from = from; + ewq.msg.arg.remap.to = to; + ewq.msg.arg.remap.len = len; + + userfaultfd_event_wait_completion(ctx, &ewq); +} + +void mremap_userfaultfd_fail(struct vm_userfaultfd_ctx *vm_ctx) +{ + struct userfaultfd_ctx *ctx = vm_ctx->ctx; + + if (!ctx) + return; + + atomic_dec(&ctx->mmap_changing); + VM_WARN_ON_ONCE(atomic_read(&ctx->mmap_changing) < 0); + userfaultfd_ctx_put(ctx); +} + +bool userfaultfd_remove(struct vm_area_struct *vma, + unsigned long start, unsigned long end) +{ + struct mm_struct *mm = vma->vm_mm; + struct userfaultfd_ctx *ctx; + struct userfaultfd_wait_queue ewq; + + ctx = vma->vm_userfaultfd_ctx.ctx; + if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE)) + return true; + + userfaultfd_ctx_get(ctx); + down_write(&ctx->map_changing_lock); + atomic_inc(&ctx->mmap_changing); + up_write(&ctx->map_changing_lock); + mmap_read_unlock(mm); + + msg_init(&ewq.msg); + + ewq.msg.event = UFFD_EVENT_REMOVE; + ewq.msg.arg.remove.start = start; + ewq.msg.arg.remove.end = end; + + userfaultfd_event_wait_completion(ctx, &ewq); + + return false; +} + +static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps, + unsigned long start, unsigned long end) +{ + struct userfaultfd_unmap_ctx *unmap_ctx; + + list_for_each_entry(unmap_ctx, unmaps, list) + if (unmap_ctx->ctx == ctx && unmap_ctx->start == start && + unmap_ctx->end == end) + return true; + + return false; +} + +int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start, + unsigned long end, struct list_head *unmaps) +{ + struct userfaultfd_unmap_ctx *unmap_ctx; + struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx; + + if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) || + has_unmap_ctx(ctx, unmaps, start, end)) + return 0; + + unmap_ctx = kzalloc_obj(*unmap_ctx); + if (!unmap_ctx) + return -ENOMEM; + + userfaultfd_ctx_get(ctx); + down_write(&ctx->map_changing_lock); + atomic_inc(&ctx->mmap_changing); + up_write(&ctx->map_changing_lock); + unmap_ctx->ctx = ctx; + unmap_ctx->start = start; + unmap_ctx->end = end; + list_add_tail(&unmap_ctx->list, unmaps); + + return 0; +} + +void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf) +{ + struct userfaultfd_unmap_ctx *ctx, *n; + struct userfaultfd_wait_queue ewq; + + list_for_each_entry_safe(ctx, n, uf, list) { + msg_init(&ewq.msg); + + ewq.msg.event = UFFD_EVENT_UNMAP; + ewq.msg.arg.remove.start = ctx->start; + ewq.msg.arg.remove.end = ctx->end; + + userfaultfd_event_wait_completion(ctx->ctx, &ewq); + + list_del(&ctx->list); + kfree(ctx); + } +} + +static int userfaultfd_release(struct inode *inode, struct file *file) +{ + struct userfaultfd_ctx *ctx = file->private_data; + struct mm_struct *mm = ctx->mm; + /* len == 0 means wake all */ + struct userfaultfd_wake_range range = { .len = 0, }; + + WRITE_ONCE(ctx->released, true); + + userfaultfd_release_all(mm, ctx); + + /* + * After no new page faults can wait on this fault_*wqh, flush + * the last page faults that may have been already waiting on + * the fault_*wqh. + */ + spin_lock_irq(&ctx->fault_pending_wqh.lock); + __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range); + __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range); + spin_unlock_irq(&ctx->fault_pending_wqh.lock); + + /* Flush pending events that may still wait on event_wqh */ + wake_up_all(&ctx->event_wqh); + + wake_up_poll(&ctx->fd_wqh, EPOLLHUP); + userfaultfd_ctx_put(ctx); + return 0; +} + +/* fault_pending_wqh.lock must be hold by the caller */ +static inline struct userfaultfd_wait_queue *find_userfault_in( + wait_queue_head_t *wqh) +{ + wait_queue_entry_t *wq; + struct userfaultfd_wait_queue *uwq; + + lockdep_assert_held(&wqh->lock); + + uwq = NULL; + if (!waitqueue_active(wqh)) + goto out; + /* walk in reverse to provide FIFO behavior to read userfaults */ + wq = list_last_entry(&wqh->head, typeof(*wq), entry); + uwq = container_of(wq, struct userfaultfd_wait_queue, wq); +out: + return uwq; +} + +static inline struct userfaultfd_wait_queue *find_userfault( + struct userfaultfd_ctx *ctx) +{ + return find_userfault_in(&ctx->fault_pending_wqh); +} + +static inline struct userfaultfd_wait_queue *find_userfault_evt( + struct userfaultfd_ctx *ctx) +{ + return find_userfault_in(&ctx->event_wqh); +} + +static __poll_t userfaultfd_poll(struct file *file, poll_table *wait) +{ + struct userfaultfd_ctx *ctx = file->private_data; + __poll_t ret; + + poll_wait(file, &ctx->fd_wqh, wait); + + if (!userfaultfd_is_initialized(ctx)) + return EPOLLERR; + + /* + * poll() never guarantees that read won't block. + * userfaults can be waken before they're read(). + */ + if (unlikely(!(file->f_flags & O_NONBLOCK))) + return EPOLLERR; + /* + * lockless access to see if there are pending faults + * __pollwait last action is the add_wait_queue but + * the spin_unlock would allow the waitqueue_active to + * pass above the actual list_add inside + * add_wait_queue critical section. So use a full + * memory barrier to serialize the list_add write of + * add_wait_queue() with the waitqueue_active read + * below. + */ + ret = 0; + smp_mb(); + if (waitqueue_active(&ctx->fault_pending_wqh)) + ret = EPOLLIN; + else if (waitqueue_active(&ctx->event_wqh)) + ret = EPOLLIN; + + return ret; +} + +static const struct file_operations userfaultfd_fops; + +static int resolve_userfault_fork(struct userfaultfd_ctx *new, + struct inode *inode, + struct uffd_msg *msg) +{ + int fd; + + fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, new, + O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode); + if (fd < 0) + return fd; + + msg->arg.reserved.reserved1 = 0; + msg->arg.fork.ufd = fd; + return 0; +} + +static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, + struct uffd_msg *msg, struct inode *inode) +{ + ssize_t ret; + DECLARE_WAITQUEUE(wait, current); + struct userfaultfd_wait_queue *uwq; + /* + * Handling fork event requires sleeping operations, so + * we drop the event_wqh lock, then do these ops, then + * lock it back and wake up the waiter. While the lock is + * dropped the ewq may go away so we keep track of it + * carefully. + */ + LIST_HEAD(fork_event); + struct userfaultfd_ctx *fork_nctx = NULL; + + /* always take the fd_wqh lock before the fault_pending_wqh lock */ + spin_lock_irq(&ctx->fd_wqh.lock); + __add_wait_queue(&ctx->fd_wqh, &wait); + for (;;) { + set_current_state(TASK_INTERRUPTIBLE); + spin_lock(&ctx->fault_pending_wqh.lock); + uwq = find_userfault(ctx); + if (uwq) { + /* + * Use a seqcount to repeat the lockless check + * in wake_userfault() to avoid missing + * wakeups because during the refile both + * waitqueue could become empty if this is the + * only userfault. + */ + write_seqcount_begin(&ctx->refile_seq); + + /* + * The fault_pending_wqh.lock prevents the uwq + * to disappear from under us. + * + * Refile this userfault from + * fault_pending_wqh to fault_wqh, it's not + * pending anymore after we read it. + * + * Use list_del() by hand (as + * userfaultfd_wake_function also uses + * list_del_init() by hand) to be sure nobody + * changes __remove_wait_queue() to use + * list_del_init() in turn breaking the + * !list_empty_careful() check in + * handle_userfault(). The uwq->wq.head list + * must never be empty at any time during the + * refile, or the waitqueue could disappear + * from under us. The "wait_queue_head_t" + * parameter of __remove_wait_queue() is unused + * anyway. + */ + list_del(&uwq->wq.entry); + add_wait_queue(&ctx->fault_wqh, &uwq->wq); + + write_seqcount_end(&ctx->refile_seq); + + /* careful to always initialize msg if ret == 0 */ + *msg = uwq->msg; + spin_unlock(&ctx->fault_pending_wqh.lock); + ret = 0; + break; + } + spin_unlock(&ctx->fault_pending_wqh.lock); + + spin_lock(&ctx->event_wqh.lock); + uwq = find_userfault_evt(ctx); + if (uwq) { + *msg = uwq->msg; + + if (uwq->msg.event == UFFD_EVENT_FORK) { + fork_nctx = (struct userfaultfd_ctx *) + (unsigned long) + uwq->msg.arg.reserved.reserved1; + list_move(&uwq->wq.entry, &fork_event); + /* + * fork_nctx can be freed as soon as + * we drop the lock, unless we take a + * reference on it. + */ + userfaultfd_ctx_get(fork_nctx); + spin_unlock(&ctx->event_wqh.lock); + ret = 0; + break; + } + + userfaultfd_event_complete(ctx, uwq); + spin_unlock(&ctx->event_wqh.lock); + ret = 0; + break; + } + spin_unlock(&ctx->event_wqh.lock); + + if (signal_pending(current)) { + ret = -ERESTARTSYS; + break; + } + if (no_wait) { + ret = -EAGAIN; + break; + } + spin_unlock_irq(&ctx->fd_wqh.lock); + schedule(); + spin_lock_irq(&ctx->fd_wqh.lock); + } + __remove_wait_queue(&ctx->fd_wqh, &wait); + __set_current_state(TASK_RUNNING); + spin_unlock_irq(&ctx->fd_wqh.lock); + + if (!ret && msg->event == UFFD_EVENT_FORK) { + ret = resolve_userfault_fork(fork_nctx, inode, msg); + spin_lock_irq(&ctx->event_wqh.lock); + if (!list_empty(&fork_event)) { + /* + * The fork thread didn't abort, so we can + * drop the temporary refcount. + */ + userfaultfd_ctx_put(fork_nctx); + + uwq = list_first_entry(&fork_event, + typeof(*uwq), + wq.entry); + /* + * If fork_event list wasn't empty and in turn + * the event wasn't already released by fork + * (the event is allocated on fork kernel + * stack), put the event back to its place in + * the event_wq. fork_event head will be freed + * as soon as we return so the event cannot + * stay queued there no matter the current + * "ret" value. + */ + list_del(&uwq->wq.entry); + __add_wait_queue(&ctx->event_wqh, &uwq->wq); + + /* + * Leave the event in the waitqueue and report + * error to userland if we failed to resolve + * the userfault fork. + */ + if (likely(!ret)) + userfaultfd_event_complete(ctx, uwq); + } else { + /* + * Here the fork thread aborted and the + * refcount from the fork thread on fork_nctx + * has already been released. We still hold + * the reference we took before releasing the + * lock above. If resolve_userfault_fork + * failed we've to drop it because the + * fork_nctx has to be freed in such case. If + * it succeeded we'll hold it because the new + * uffd references it. + */ + if (ret) + userfaultfd_ctx_put(fork_nctx); + } + spin_unlock_irq(&ctx->event_wqh.lock); + } + + return ret; +} + +static ssize_t userfaultfd_read_iter(struct kiocb *iocb, struct iov_iter *to) +{ + struct file *file = iocb->ki_filp; + struct userfaultfd_ctx *ctx = file->private_data; + ssize_t _ret, ret = 0; + struct uffd_msg msg; + struct inode *inode = file_inode(file); + bool no_wait; + + if (!userfaultfd_is_initialized(ctx)) + return -EINVAL; + + no_wait = file->f_flags & O_NONBLOCK || iocb->ki_flags & IOCB_NOWAIT; + for (;;) { + if (iov_iter_count(to) < sizeof(msg)) + return ret ? ret : -EINVAL; + _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode); + if (_ret < 0) + return ret ? ret : _ret; + _ret = !copy_to_iter_full(&msg, sizeof(msg), to); + if (_ret) + return ret ? ret : -EFAULT; + ret += sizeof(msg); + /* + * Allow to read more than one fault at time but only + * block if waiting for the very first one. + */ + no_wait = true; + } +} + +static void __wake_userfault(struct userfaultfd_ctx *ctx, + struct userfaultfd_wake_range *range) +{ + spin_lock_irq(&ctx->fault_pending_wqh.lock); + /* wake all in the range and autoremove */ + if (waitqueue_active(&ctx->fault_pending_wqh)) + __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, + range); + if (waitqueue_active(&ctx->fault_wqh)) + __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range); + spin_unlock_irq(&ctx->fault_pending_wqh.lock); +} + +static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, + struct userfaultfd_wake_range *range) +{ + unsigned seq; + bool need_wakeup; + + /* + * To be sure waitqueue_active() is not reordered by the CPU + * before the pagetable update, use an explicit SMP memory + * barrier here. PT lock release or mmap_read_unlock(mm) still + * have release semantics that can allow the + * waitqueue_active() to be reordered before the pte update. + */ + smp_mb(); + + /* + * Use waitqueue_active because it's very frequent to + * change the address space atomically even if there are no + * userfaults yet. So we take the spinlock only when we're + * sure we've userfaults to wake. + */ + do { + seq = read_seqcount_begin(&ctx->refile_seq); + need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) || + waitqueue_active(&ctx->fault_wqh); + cond_resched(); + } while (read_seqcount_retry(&ctx->refile_seq, seq)); + if (need_wakeup) + __wake_userfault(ctx, range); +} + +static __always_inline int validate_unaligned_range( + struct mm_struct *mm, __u64 start, __u64 len) +{ + __u64 task_size = mm->task_size; + + if (len & ~PAGE_MASK) + return -EINVAL; + if (!len) + return -EINVAL; + if (start >= task_size) + return -EINVAL; + if (len > task_size - start) + return -EINVAL; + if (start + len <= start) + return -EINVAL; + return 0; +} + +static __always_inline int validate_range(struct mm_struct *mm, + __u64 start, __u64 len) +{ + if (start & ~PAGE_MASK) + return -EINVAL; + + return validate_unaligned_range(mm, start, len); +} + +static int userfaultfd_register(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + struct mm_struct *mm = ctx->mm; + struct vm_area_struct *vma, *cur; + int ret; + struct uffdio_register uffdio_register; + struct uffdio_register __user *user_uffdio_register; + vm_flags_t vm_flags; + bool found; + bool basic_ioctls; + unsigned long start, end; + struct vma_iterator vmi; + bool wp_async = userfaultfd_wp_async_ctx(ctx); + + user_uffdio_register = (struct uffdio_register __user *) arg; + + ret = -EFAULT; + if (copy_from_user(&uffdio_register, user_uffdio_register, + sizeof(uffdio_register)-sizeof(__u64))) + goto out; + + ret = -EINVAL; + if (!uffdio_register.mode) + goto out; + if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES) + goto out; + vm_flags = 0; + if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING) + vm_flags |= VM_UFFD_MISSING; + if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) { + if (!pgtable_supports_uffd()) + goto out; + + vm_flags |= VM_UFFD_WP; + } + if (uffdio_register.mode & UFFDIO_REGISTER_MODE_RWP) { + if (!pgtable_supports_uffd() || VM_UFFD_RWP == VM_NONE) + goto out; + if (!(userfaultfd_features(ctx) & UFFD_FEATURE_RWP)) + goto out; + vm_flags |= VM_UFFD_RWP; + } + + /* + * WP and RWP share the uffd PTE bit and + * cannot coexist in the same VMA — the bit would carry ambiguous + * semantics. Reject the combination up front. + */ + if ((vm_flags & VM_UFFD_WP) && (vm_flags & VM_UFFD_RWP)) + goto out; + + if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) { +#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR + goto out; +#endif + vm_flags |= VM_UFFD_MINOR; + } + + ret = validate_range(mm, uffdio_register.range.start, + uffdio_register.range.len); + if (ret) + goto out; + + start = uffdio_register.range.start; + end = start + uffdio_register.range.len; + + ret = -ENOMEM; + if (!mmget_not_zero(mm)) + goto out; + + ret = -EINVAL; + mmap_write_lock(mm); + vma_iter_init(&vmi, mm, start); + vma = vma_find(&vmi, end); + if (!vma) + goto out_unlock; + + /* + * If the first vma contains huge pages, make sure start address + * is aligned to huge page size. + */ + if (is_vm_hugetlb_page(vma)) { + unsigned long vma_hpagesize = vma_kernel_pagesize(vma); + + if (start & (vma_hpagesize - 1)) + goto out_unlock; + } + + /* + * Search for not compatible vmas. + */ + found = false; + basic_ioctls = false; + cur = vma; + do { + cond_resched(); + + VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^ + !!(cur->vm_flags & __VM_UFFD_FLAGS)); + + /* check not compatible vmas */ + ret = -EINVAL; + if (!vma_can_userfault(cur, vm_flags, wp_async)) + goto out_unlock; + + /* + * RWP uses protnone as an access-tracking marker. PROT_NONE + * VMAs have vm_page_prot == PAGE_NONE, so RWP resolution + * cannot make a page accessible again. Reject at register + * time only: a VMA that later becomes inaccessible via + * mprotect() must still be unregisterable, so this is not + * part of vma_can_userfault(). + */ + if ((vm_flags & VM_UFFD_RWP) && !vma_is_accessible(cur)) + goto out_unlock; + + /* + * UFFDIO_COPY will fill file holes even without + * PROT_WRITE. This check enforces that if this is a + * MAP_SHARED, the process has write permission to the backing + * file. If VM_MAYWRITE is set it also enforces that on a + * MAP_SHARED vma: there is no F_WRITE_SEAL and no further + * F_WRITE_SEAL can be taken until the vma is destroyed. + */ + ret = -EPERM; + if (unlikely(!(cur->vm_flags & VM_MAYWRITE))) + goto out_unlock; + + /* + * If this vma contains ending address, and huge pages + * check alignment. + */ + if (is_vm_hugetlb_page(cur) && end <= cur->vm_end && + end > cur->vm_start) { + unsigned long vma_hpagesize = vma_kernel_pagesize(cur); + + ret = -EINVAL; + + if (end & (vma_hpagesize - 1)) + goto out_unlock; + } + if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE)) + goto out_unlock; + + /* + * Check that this vma isn't already owned by a + * different userfaultfd. We can't allow more than one + * userfaultfd to own a single vma simultaneously or we + * wouldn't know which one to deliver the userfaults to. + */ + ret = -EBUSY; + if (cur->vm_userfaultfd_ctx.ctx && + cur->vm_userfaultfd_ctx.ctx != ctx) + goto out_unlock; + + /* + * Mode switches that drop VM_UFFD_WP or VM_UFFD_RWP would + * leave PTE markers without the flag that describes them; + * subsequent mprotect() would then promote stale markers + * into the other mode. Require an unregister first. + */ + if (cur->vm_userfaultfd_ctx.ctx == ctx && + cur->vm_flags & (VM_UFFD_WP | VM_UFFD_RWP) & ~vm_flags) + goto out_unlock; + + /* + * Note vmas containing huge pages + */ + if (is_vm_hugetlb_page(cur)) + basic_ioctls = true; + + found = true; + } for_each_vma_range(vmi, cur, end); + VM_WARN_ON_ONCE(!found); + + ret = userfaultfd_register_range(ctx, vma, vm_flags, start, end, + wp_async); + +out_unlock: + mmap_write_unlock(mm); + mmput(mm); + if (!ret) { + __u64 ioctls_out; + + ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC : + UFFD_API_RANGE_IOCTLS; + + /* + * Declare the WP ioctl only if the WP mode is + * specified and all checks passed with the range + */ + if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)) + ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT); + + /* CONTINUE ioctl is only supported for MINOR ranges. */ + if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR)) + ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE); + + /* RWPROTECT is only supported for RWP ranges */ + if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_RWP)) + ioctls_out &= ~((__u64)1 << _UFFDIO_RWPROTECT); + + /* + * Now that we scanned all vmas we can already tell + * userland which ioctls methods are guaranteed to + * succeed on this range. + */ + if (put_user(ioctls_out, &user_uffdio_register->ioctls)) + ret = -EFAULT; + } +out: + return ret; +} + +static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + struct mm_struct *mm = ctx->mm; + struct vm_area_struct *vma, *prev, *cur; + int ret; + struct uffdio_range uffdio_unregister; + bool found; + unsigned long start, end, vma_end; + const void __user *buf = (void __user *)arg; + struct vma_iterator vmi; + bool wp_async = userfaultfd_wp_async_ctx(ctx); + + ret = -EFAULT; + if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister))) + goto out; + + ret = validate_range(mm, uffdio_unregister.start, + uffdio_unregister.len); + if (ret) + goto out; + + start = uffdio_unregister.start; + end = start + uffdio_unregister.len; + + ret = -ENOMEM; + if (!mmget_not_zero(mm)) + goto out; + + mmap_write_lock(mm); + ret = -EINVAL; + vma_iter_init(&vmi, mm, start); + vma = vma_find(&vmi, end); + if (!vma) + goto out_unlock; + + /* + * If the first vma contains huge pages, make sure start address + * is aligned to huge page size. + */ + if (is_vm_hugetlb_page(vma)) { + unsigned long vma_hpagesize = vma_kernel_pagesize(vma); + + if (start & (vma_hpagesize - 1)) + goto out_unlock; + } + + /* + * Search for not compatible vmas. + */ + found = false; + cur = vma; + do { + cond_resched(); + + VM_WARN_ON_ONCE(!!cur->vm_userfaultfd_ctx.ctx ^ + !!(cur->vm_flags & __VM_UFFD_FLAGS)); + + /* + * Prevent unregistering through a different userfaultfd than + * the one used for registration. + */ + if (cur->vm_userfaultfd_ctx.ctx && + cur->vm_userfaultfd_ctx.ctx != ctx) + goto out_unlock; + + /* + * Check not compatible vmas, not strictly required + * here as not compatible vmas cannot have an + * userfaultfd_ctx registered on them, but this + * provides for more strict behavior to notice + * unregistration errors. + */ + if (!vma_can_userfault(cur, cur->vm_flags, wp_async)) + goto out_unlock; + + found = true; + } for_each_vma_range(vmi, cur, end); + VM_WARN_ON_ONCE(!found); + + vma_iter_set(&vmi, start); + prev = vma_prev(&vmi); + if (vma->vm_start < start) + prev = vma; + + ret = 0; + for_each_vma_range(vmi, vma, end) { + cond_resched(); + + /* VMA not registered with userfaultfd. */ + if (!vma->vm_userfaultfd_ctx.ctx) + goto skip; + + VM_WARN_ON_ONCE(vma->vm_userfaultfd_ctx.ctx != ctx); + VM_WARN_ON_ONCE(!vma_can_userfault(vma, vma->vm_flags, wp_async)); + VM_WARN_ON_ONCE(!(vma->vm_flags & VM_MAYWRITE)); + + if (vma->vm_start > start) + start = vma->vm_start; + vma_end = min(end, vma->vm_end); + + if (userfaultfd_missing(vma)) { + /* + * Wake any concurrent pending userfault while + * we unregister, so they will not hang + * permanently and it avoids userland to call + * UFFDIO_WAKE explicitly. + */ + struct userfaultfd_wake_range range; + range.start = start; + range.len = vma_end - start; + wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range); + } + + vma = userfaultfd_clear_vma(&vmi, prev, vma, + start, vma_end); + if (IS_ERR(vma)) { + ret = PTR_ERR(vma); + break; + } + +skip: + prev = vma; + start = vma->vm_end; + } + +out_unlock: + mmap_write_unlock(mm); + mmput(mm); +out: + return ret; +} + +/* + * userfaultfd_wake may be used in combination with the + * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches. + */ +static int userfaultfd_wake(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + int ret; + struct uffdio_range uffdio_wake; + struct userfaultfd_wake_range range; + const void __user *buf = (void __user *)arg; + + ret = -EFAULT; + if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake))) + goto out; + + ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len); + if (ret) + goto out; + + range.start = uffdio_wake.start; + range.len = uffdio_wake.len; + + /* + * len == 0 means wake all and we don't want to wake all here, + * so check it again to be sure. + */ + VM_WARN_ON_ONCE(!range.len); + + wake_userfault(ctx, &range); + ret = 0; + +out: + return ret; +} + +static int userfaultfd_copy(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + __s64 ret; + struct uffdio_copy uffdio_copy; + struct uffdio_copy __user *user_uffdio_copy; + struct userfaultfd_wake_range range; + uffd_flags_t flags = 0; + + user_uffdio_copy = (struct uffdio_copy __user *) arg; + + ret = -EAGAIN; + if (unlikely(atomic_read(&ctx->mmap_changing))) { + if (unlikely(put_user(ret, &user_uffdio_copy->copy))) + return -EFAULT; + goto out; + } + + ret = -EFAULT; + if (copy_from_user(&uffdio_copy, user_uffdio_copy, + /* don't copy "copy" last field */ + sizeof(uffdio_copy)-sizeof(__s64))) + goto out; + + ret = validate_unaligned_range(ctx->mm, uffdio_copy.src, + uffdio_copy.len); + if (ret) + goto out; + ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len); + if (ret) + goto out; + + ret = -EINVAL; + if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP)) + goto out; + if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP) + flags |= MFILL_ATOMIC_WP; + if (mmget_not_zero(ctx->mm)) { + ret = mfill_atomic_copy(ctx, uffdio_copy.dst, uffdio_copy.src, + uffdio_copy.len, flags); + mmput(ctx->mm); + } else { + return -ESRCH; + } + if (unlikely(put_user(ret, &user_uffdio_copy->copy))) + return -EFAULT; + if (ret < 0) + goto out; + VM_WARN_ON_ONCE(!ret); + /* len == 0 would wake all */ + range.len = ret; + if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) { + range.start = uffdio_copy.dst; + wake_userfault(ctx, &range); + } + ret = range.len == uffdio_copy.len ? 0 : -EAGAIN; +out: + return ret; +} + +static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + __s64 ret; + struct uffdio_zeropage uffdio_zeropage; + struct uffdio_zeropage __user *user_uffdio_zeropage; + struct userfaultfd_wake_range range; + + user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg; + + ret = -EAGAIN; + if (unlikely(atomic_read(&ctx->mmap_changing))) { + if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage))) + return -EFAULT; + goto out; + } + + ret = -EFAULT; + if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage, + /* don't copy "zeropage" last field */ + sizeof(uffdio_zeropage)-sizeof(__s64))) + goto out; + + ret = validate_range(ctx->mm, uffdio_zeropage.range.start, + uffdio_zeropage.range.len); + if (ret) + goto out; + ret = -EINVAL; + if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE) + goto out; + + if (mmget_not_zero(ctx->mm)) { + ret = mfill_atomic_zeropage(ctx, uffdio_zeropage.range.start, + uffdio_zeropage.range.len); + mmput(ctx->mm); + } else { + return -ESRCH; + } + if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage))) + return -EFAULT; + if (ret < 0) + goto out; + /* len == 0 would wake all */ + VM_WARN_ON_ONCE(!ret); + range.len = ret; + if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) { + range.start = uffdio_zeropage.range.start; + wake_userfault(ctx, &range); + } + ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN; +out: + return ret; +} + +static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + int ret; + struct uffdio_writeprotect uffdio_wp; + struct uffdio_writeprotect __user *user_uffdio_wp; + struct userfaultfd_wake_range range; + bool mode_wp, mode_dontwake; + + if (atomic_read(&ctx->mmap_changing)) + return -EAGAIN; + + user_uffdio_wp = (struct uffdio_writeprotect __user *) arg; + + if (copy_from_user(&uffdio_wp, user_uffdio_wp, + sizeof(struct uffdio_writeprotect))) + return -EFAULT; + + ret = validate_range(ctx->mm, uffdio_wp.range.start, + uffdio_wp.range.len); + if (ret) + return ret; + + if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE | + UFFDIO_WRITEPROTECT_MODE_WP)) + return -EINVAL; + + mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP; + mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE; + + if (mode_wp && mode_dontwake) + return -EINVAL; + + if (mmget_not_zero(ctx->mm)) { + ret = mwriteprotect_range(ctx, uffdio_wp.range.start, + uffdio_wp.range.len, mode_wp); + mmput(ctx->mm); + } else { + return -ESRCH; + } + + if (ret) + return ret; + + if (!mode_wp && !mode_dontwake) { + range.start = uffdio_wp.range.start; + range.len = uffdio_wp.range.len; + wake_userfault(ctx, &range); + } + return ret; +} + +static int userfaultfd_rwprotect(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + int ret; + struct uffdio_rwprotect uffdio_rwp; + struct userfaultfd_wake_range range; + bool mode_rwp, mode_dontwake; + + if (atomic_read(&ctx->mmap_changing)) + return -EAGAIN; + + if (copy_from_user(&uffdio_rwp, (void __user *)arg, + sizeof(uffdio_rwp))) + return -EFAULT; + + ret = validate_range(ctx->mm, uffdio_rwp.range.start, + uffdio_rwp.range.len); + if (ret) + return ret; + + if (uffdio_rwp.mode & ~(UFFDIO_RWPROTECT_MODE_DONTWAKE | + UFFDIO_RWPROTECT_MODE_RWP)) + return -EINVAL; + + mode_rwp = uffdio_rwp.mode & UFFDIO_RWPROTECT_MODE_RWP; + mode_dontwake = uffdio_rwp.mode & UFFDIO_RWPROTECT_MODE_DONTWAKE; + + if (mode_rwp && mode_dontwake) + return -EINVAL; + + if (mmget_not_zero(ctx->mm)) { + ret = mrwprotect_range(ctx, uffdio_rwp.range.start, + uffdio_rwp.range.len, mode_rwp); + mmput(ctx->mm); + } else { + return -ESRCH; + } + + if (ret) + return ret; + + if (!mode_rwp && !mode_dontwake) { + range.start = uffdio_rwp.range.start; + range.len = uffdio_rwp.range.len; + wake_userfault(ctx, &range); + } + return ret; +} + +/* Subset of UFFD_API_FEATURES actually supported by this kernel/arch */ +static __u64 uffd_api_available_features(void) +{ + __u64 f = UFFD_API_FEATURES; + + if (!IS_ENABLED(CONFIG_HAVE_ARCH_USERFAULTFD_MINOR)) + f &= ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM); + if (!pgtable_supports_uffd()) + f &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP; + if (!uffd_supports_wp_marker()) + f &= ~(UFFD_FEATURE_WP_HUGETLBFS_SHMEM | + UFFD_FEATURE_WP_UNPOPULATED | + UFFD_FEATURE_WP_ASYNC); + /* + * RWP needs both PROT_NONE support and the uffd PTE bit. The + * VM_UFFD_RWP check covers compile-time unavailability; the + * pgtable_supports_uffd() check covers runtime (e.g. riscv + * without the SVRSW60T59B extension) where the PTE bit is declared + * but not actually usable. + */ + if (VM_UFFD_RWP == VM_NONE || !pgtable_supports_uffd()) + f &= ~(UFFD_FEATURE_RWP | UFFD_FEATURE_RWP_ASYNC); + return f; +} + +/* Async features that can be toggled at runtime via UFFDIO_SET_MODE */ +#define UFFD_FEATURE_TOGGLEABLE UFFD_FEATURE_RWP_ASYNC + +static int userfaultfd_set_mode(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + struct uffdio_set_mode mode; + struct mm_struct *mm = ctx->mm; + + if (copy_from_user(&mode, (void __user *)arg, sizeof(mode))) + return -EFAULT; + + /* enable and disable must not overlap */ + if (mode.enable & mode.disable) + return -EINVAL; + + /* only toggleable features that this kernel/arch actually supports */ + if ((mode.enable | mode.disable) & + ~(uffd_api_available_features() & UFFD_FEATURE_TOGGLEABLE)) + return -EINVAL; + + /* RWP_ASYNC can only be enabled on contexts that negotiated RWP */ + if ((mode.enable & UFFD_FEATURE_RWP_ASYNC) && + !(userfaultfd_features(ctx) & UFFD_FEATURE_RWP)) + return -EINVAL; + + if (!mmget_not_zero(mm)) + return -ESRCH; + + /* + * Drain in-flight faults before flipping features. mmap_write_lock() + * blocks new mmap_read_lock() callers, but per-VMA locked faults + * (lock_vma_under_rcu() + FAULT_FLAG_VMA_LOCK) that acquired before + * this point keep running. Calling vma_start_write() on each UFFD- + * armed VMA waits for those readers to drop, so no in-flight fault + * can observe the old features after mmap_write_unlock(). + */ + mmap_write_lock(mm); + { + struct vm_area_struct *vma; + VMA_ITERATOR(vmi, mm, 0); + + for_each_vma(vmi, vma) { + if (vma->vm_userfaultfd_ctx.ctx == ctx) + vma_start_write(vma); + } + } + /* + * Single WRITE_ONCE so lockless readers (fdinfo, poll/read_iter + * via userfaultfd_is_initialized(), and the userfaultfd_features() + * helper used elsewhere) can't observe a mid-RMW intermediate + * value. Hot-path readers already serialise through the mmap lock + * + vma_start_write() drain above, so their load doesn't need an + * annotation. + */ + WRITE_ONCE(ctx->features, + (ctx->features | mode.enable) & ~mode.disable); + mmap_write_unlock(mm); + + /* + * If switching to async, wake threads blocked in handle_userfault(). + * They will retry the fault and auto-resolve under the new mode. + * len=0 means wake all pending faults on this context. + */ + if (mode.enable & UFFD_FEATURE_RWP_ASYNC) { + struct userfaultfd_wake_range range = { .len = 0 }; + + spin_lock_irq(&ctx->fault_pending_wqh.lock); + __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, + &range); + __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range); + spin_unlock_irq(&ctx->fault_pending_wqh.lock); + } + + mmput(mm); + return 0; +} + +static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg) +{ + __s64 ret; + struct uffdio_continue uffdio_continue; + struct uffdio_continue __user *user_uffdio_continue; + struct userfaultfd_wake_range range; + uffd_flags_t flags = 0; + + user_uffdio_continue = (struct uffdio_continue __user *)arg; + + ret = -EAGAIN; + if (unlikely(atomic_read(&ctx->mmap_changing))) { + if (unlikely(put_user(ret, &user_uffdio_continue->mapped))) + return -EFAULT; + goto out; + } + + ret = -EFAULT; + if (copy_from_user(&uffdio_continue, user_uffdio_continue, + /* don't copy the output fields */ + sizeof(uffdio_continue) - (sizeof(__s64)))) + goto out; + + ret = validate_range(ctx->mm, uffdio_continue.range.start, + uffdio_continue.range.len); + if (ret) + goto out; + + ret = -EINVAL; + if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE | + UFFDIO_CONTINUE_MODE_WP)) + goto out; + if (uffdio_continue.mode & UFFDIO_CONTINUE_MODE_WP) + flags |= MFILL_ATOMIC_WP; + + if (mmget_not_zero(ctx->mm)) { + ret = mfill_atomic_continue(ctx, uffdio_continue.range.start, + uffdio_continue.range.len, flags); + mmput(ctx->mm); + } else { + return -ESRCH; + } + + if (unlikely(put_user(ret, &user_uffdio_continue->mapped))) + return -EFAULT; + if (ret < 0) + goto out; + + /* len == 0 would wake all */ + VM_WARN_ON_ONCE(!ret); + range.len = ret; + if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) { + range.start = uffdio_continue.range.start; + wake_userfault(ctx, &range); + } + ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN; + +out: + return ret; +} + +static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg) +{ + __s64 ret; + struct uffdio_poison uffdio_poison; + struct uffdio_poison __user *user_uffdio_poison; + struct userfaultfd_wake_range range; + + user_uffdio_poison = (struct uffdio_poison __user *)arg; + + ret = -EAGAIN; + if (unlikely(atomic_read(&ctx->mmap_changing))) { + if (unlikely(put_user(ret, &user_uffdio_poison->updated))) + return -EFAULT; + goto out; + } + + ret = -EFAULT; + if (copy_from_user(&uffdio_poison, user_uffdio_poison, + /* don't copy the output fields */ + sizeof(uffdio_poison) - (sizeof(__s64)))) + goto out; + + ret = validate_range(ctx->mm, uffdio_poison.range.start, + uffdio_poison.range.len); + if (ret) + goto out; + + ret = -EINVAL; + if (uffdio_poison.mode & ~UFFDIO_POISON_MODE_DONTWAKE) + goto out; + + if (mmget_not_zero(ctx->mm)) { + ret = mfill_atomic_poison(ctx, uffdio_poison.range.start, + uffdio_poison.range.len, 0); + mmput(ctx->mm); + } else { + return -ESRCH; + } + + if (unlikely(put_user(ret, &user_uffdio_poison->updated))) + return -EFAULT; + if (ret < 0) + goto out; + + /* len == 0 would wake all */ + VM_WARN_ON_ONCE(!ret); + range.len = ret; + if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) { + range.start = uffdio_poison.range.start; + wake_userfault(ctx, &range); + } + ret = range.len == uffdio_poison.range.len ? 0 : -EAGAIN; + +out: + return ret; +} + +bool userfaultfd_wp_async(struct vm_area_struct *vma) +{ + return userfaultfd_wp_async_ctx(vma->vm_userfaultfd_ctx.ctx); +} + +bool userfaultfd_rwp_async(struct vm_area_struct *vma) +{ + return userfaultfd_rwp_async_ctx(vma->vm_userfaultfd_ctx.ctx); +} + +static inline unsigned int uffd_ctx_features(__u64 user_features) +{ + /* + * For the current set of features the bits just coincide. Set + * UFFD_FEATURE_INITIALIZED to mark the features as enabled. + */ + return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED; +} + +static int userfaultfd_move(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + __s64 ret; + struct uffdio_move uffdio_move; + struct uffdio_move __user *user_uffdio_move; + struct userfaultfd_wake_range range; + struct mm_struct *mm = ctx->mm; + + user_uffdio_move = (struct uffdio_move __user *) arg; + + ret = -EAGAIN; + if (unlikely(atomic_read(&ctx->mmap_changing))) { + if (unlikely(put_user(ret, &user_uffdio_move->move))) + return -EFAULT; + goto out; + } + + if (copy_from_user(&uffdio_move, user_uffdio_move, + /* don't copy "move" last field */ + sizeof(uffdio_move)-sizeof(__s64))) + return -EFAULT; + + /* Do not allow cross-mm moves. */ + if (mm != current->mm) + return -EINVAL; + + ret = validate_range(mm, uffdio_move.dst, uffdio_move.len); + if (ret) + return ret; + + ret = validate_range(mm, uffdio_move.src, uffdio_move.len); + if (ret) + return ret; + + if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES| + UFFDIO_MOVE_MODE_DONTWAKE)) + return -EINVAL; + + if (mmget_not_zero(mm)) { + ret = move_pages(ctx, uffdio_move.dst, uffdio_move.src, + uffdio_move.len, uffdio_move.mode); + mmput(mm); + } else { + return -ESRCH; + } + + if (unlikely(put_user(ret, &user_uffdio_move->move))) + return -EFAULT; + if (ret < 0) + goto out; + + /* len == 0 would wake all */ + VM_WARN_ON(!ret); + range.len = ret; + if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) { + range.start = uffdio_move.dst; + wake_userfault(ctx, &range); + } + ret = range.len == uffdio_move.len ? 0 : -EAGAIN; + +out: + return ret; +} + +/* + * userland asks for a certain API version and we return which bits + * and ioctl commands are implemented in this kernel for such API + * version or -EINVAL if unknown. + */ +static int userfaultfd_api(struct userfaultfd_ctx *ctx, + unsigned long arg) +{ + struct uffdio_api uffdio_api; + void __user *buf = (void __user *)arg; + unsigned int ctx_features; + int ret; + __u64 features; + + ret = -EFAULT; + if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) + goto out; + features = uffdio_api.features; + ret = -EINVAL; + if (uffdio_api.api != UFFD_API) + goto err_out; + ret = -EPERM; + if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE)) + goto err_out; + + /* WP_ASYNC relies on WP_UNPOPULATED, choose it unconditionally */ + if (features & UFFD_FEATURE_WP_ASYNC) + features |= UFFD_FEATURE_WP_UNPOPULATED; + + ret = -EINVAL; + /* RWP_ASYNC requires RWP */ + if ((features & UFFD_FEATURE_RWP_ASYNC) && + !(features & UFFD_FEATURE_RWP)) + goto err_out; + + /* report all available features and ioctls to userland */ + uffdio_api.features = uffd_api_available_features(); + + ret = -EINVAL; + if (features & ~uffdio_api.features) + goto err_out; + + uffdio_api.ioctls = UFFD_API_IOCTLS; + ret = -EFAULT; + if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) + goto out; + + /* only enable the requested features for this uffd context */ + ctx_features = uffd_ctx_features(features); + ret = -EINVAL; + if (cmpxchg(&ctx->features, 0, ctx_features) != 0) + goto err_out; + + ret = 0; +out: + return ret; +err_out: + memset(&uffdio_api, 0, sizeof(uffdio_api)); + if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) + ret = -EFAULT; + goto out; +} + +static long userfaultfd_ioctl(struct file *file, unsigned cmd, + unsigned long arg) +{ + int ret = -EINVAL; + struct userfaultfd_ctx *ctx = file->private_data; + + if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx)) + return -EINVAL; + + switch (cmd) { + case UFFDIO_API: + ret = userfaultfd_api(ctx, arg); + break; + case UFFDIO_REGISTER: + ret = userfaultfd_register(ctx, arg); + break; + case UFFDIO_UNREGISTER: + ret = userfaultfd_unregister(ctx, arg); + break; + case UFFDIO_WAKE: + ret = userfaultfd_wake(ctx, arg); + break; + case UFFDIO_COPY: + ret = userfaultfd_copy(ctx, arg); + break; + case UFFDIO_ZEROPAGE: + ret = userfaultfd_zeropage(ctx, arg); + break; + case UFFDIO_MOVE: + ret = userfaultfd_move(ctx, arg); + break; + case UFFDIO_WRITEPROTECT: + ret = userfaultfd_writeprotect(ctx, arg); + break; + case UFFDIO_CONTINUE: + ret = userfaultfd_continue(ctx, arg); + break; + case UFFDIO_POISON: + ret = userfaultfd_poison(ctx, arg); + break; + case UFFDIO_RWPROTECT: + ret = userfaultfd_rwprotect(ctx, arg); + break; + case UFFDIO_SET_MODE: + ret = userfaultfd_set_mode(ctx, arg); + break; + } + return ret; +} + +#ifdef CONFIG_PROC_FS +static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f) +{ + struct userfaultfd_ctx *ctx = f->private_data; + wait_queue_entry_t *wq; + unsigned long pending = 0, total = 0; + + spin_lock_irq(&ctx->fault_pending_wqh.lock); + list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) { + pending++; + total++; + } + list_for_each_entry(wq, &ctx->fault_wqh.head, entry) { + total++; + } + spin_unlock_irq(&ctx->fault_pending_wqh.lock); + + /* + * If more protocols will be added, there will be all shown + * separated by a space. Like this: + * protocols: aa:... bb:... + */ + seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n", + pending, total, UFFD_API, userfaultfd_features(ctx), + UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS); +} +#endif + +static const struct file_operations userfaultfd_fops = { +#ifdef CONFIG_PROC_FS + .show_fdinfo = userfaultfd_show_fdinfo, +#endif + .release = userfaultfd_release, + .poll = userfaultfd_poll, + .read_iter = userfaultfd_read_iter, + .unlocked_ioctl = userfaultfd_ioctl, + .compat_ioctl = compat_ptr_ioctl, + .llseek = noop_llseek, +}; + +static void init_once_userfaultfd_ctx(void *mem) +{ + struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem; + + init_waitqueue_head(&ctx->fault_pending_wqh); + init_waitqueue_head(&ctx->fault_wqh); + init_waitqueue_head(&ctx->event_wqh); + init_waitqueue_head(&ctx->fd_wqh); + seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock); +} + +static int new_userfaultfd(int flags) +{ + struct userfaultfd_ctx *ctx __free(kfree) = NULL; + + VM_WARN_ON_ONCE(!current->mm); + + /* Check the UFFD_* constants for consistency. */ + BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS); + + if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY)) + return -EINVAL; + + ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); + if (!ctx) + return -ENOMEM; + + refcount_set(&ctx->refcount, 1); + ctx->flags = flags; + ctx->features = 0; + ctx->released = false; + init_rwsem(&ctx->map_changing_lock); + atomic_set(&ctx->mmap_changing, 0); + ctx->mm = current->mm; + + FD_PREPARE(fdf, flags & UFFD_SHARED_FCNTL_FLAGS, + anon_inode_create_getfile("[userfaultfd]", &userfaultfd_fops, ctx, + O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), + NULL)); + if (fdf.err) + return fdf.err; + + /* prevent the mm struct to be freed */ + mmgrab(ctx->mm); + fd_prepare_file(fdf)->f_mode |= FMODE_NOWAIT; + retain_and_null_ptr(ctx); + return fd_publish(fdf); +} + +static inline bool userfaultfd_syscall_allowed(int flags) +{ + /* Userspace-only page faults are always allowed */ + if (flags & UFFD_USER_MODE_ONLY) + return true; + + /* + * The user is requesting a userfaultfd which can handle kernel faults. + * Privileged users are always allowed to do this. + */ + if (capable(CAP_SYS_PTRACE)) + return true; + + /* Otherwise, access to kernel fault handling is sysctl controlled. */ + return sysctl_unprivileged_userfaultfd; +} + +SYSCALL_DEFINE1(userfaultfd, int, flags) +{ + if (!userfaultfd_syscall_allowed(flags)) + return -EPERM; + + return new_userfaultfd(flags); +} + +static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags) +{ + if (cmd != USERFAULTFD_IOC_NEW) + return -EINVAL; + + return new_userfaultfd(flags); +} + +static const struct file_operations userfaultfd_dev_fops = { + .unlocked_ioctl = userfaultfd_dev_ioctl, + .compat_ioctl = userfaultfd_dev_ioctl, + .owner = THIS_MODULE, + .llseek = noop_llseek, +}; + +static struct miscdevice userfaultfd_misc = { + .minor = MISC_DYNAMIC_MINOR, + .name = "userfaultfd", + .fops = &userfaultfd_dev_fops +}; + +static int __init userfaultfd_init(void) +{ + int ret; + + ret = misc_register(&userfaultfd_misc); + if (ret) + return ret; + + userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache", + sizeof(struct userfaultfd_ctx), + 0, + SLAB_HWCACHE_ALIGN|SLAB_PANIC, + init_once_userfaultfd_ctx); +#ifdef CONFIG_SYSCTL + register_sysctl_init("vm", vm_userfaultfd_table); +#endif + return 0; +} +__initcall(userfaultfd_init); |