From c08e6a1206e6876c66e0528b3ec717f557b07dd4 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Thu, 24 Mar 2022 18:11:07 -0700 Subject: kasan, fork: reset pointer tags of vmapped stacks Once tag-based KASAN modes start tagging vmalloc() allocations, kernel stacks start getting tagged if CONFIG_VMAP_STACK is enabled. Reset the tag of kernel stack pointers after allocation in alloc_thread_stack_node(). For SW_TAGS KASAN, when CONFIG_KASAN_STACK is enabled, the instrumentation can't handle the SP register being tagged. For HW_TAGS KASAN, there's no instrumentation-related issues. However, the impact of having a tagged SP register needs to be properly evaluated, so keep it non-tagged for now. Note, that the memory for the stack allocation still gets tagged to catch vmalloc-into-stack out-of-bounds accesses. Link: https://lkml.kernel.org/r/c6c96f012371ecd80e1936509ebcd3b07a5956f7.1643047180.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Reviewed-by: Alexander Potapenko Acked-by: Marco Elver Cc: Andrey Ryabinin Cc: Catalin Marinas Cc: Dmitry Vyukov Cc: Evgenii Stepanov Cc: Mark Rutland Cc: Peter Collingbourne Cc: Vincenzo Frascino Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'kernel') diff --git a/kernel/fork.c b/kernel/fork.c index 834af51ed397..ce0ffe48937f 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -326,6 +326,8 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) * so cache the vm_struct. */ tsk->stack_vm_area = vm; + if (stack) + stack = kasan_reset_tag(stack); tsk->stack = stack; return 0; } -- cgit v1.2.3 From 51fb34de2a4c8fa0f221246313700bfe3b6c586d Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Thu, 24 Mar 2022 18:11:10 -0700 Subject: kasan, arm64: reset pointer tags of vmapped stacks Once tag-based KASAN modes start tagging vmalloc() allocations, kernel stacks start getting tagged if CONFIG_VMAP_STACK is enabled. Reset the tag of kernel stack pointers after allocation in arch_alloc_vmap_stack(). For SW_TAGS KASAN, when CONFIG_KASAN_STACK is enabled, the instrumentation can't handle the SP register being tagged. For HW_TAGS KASAN, there's no instrumentation-related issues. However, the impact of having a tagged SP register needs to be properly evaluated, so keep it non-tagged for now. Note, that the memory for the stack allocation still gets tagged to catch vmalloc-into-stack out-of-bounds accesses. [andreyknvl@google.com: fix case when a stack is retrieved from cached_stacks] Link: https://lkml.kernel.org/r/f50c5f96ef896d7936192c888b0c0a7674e33184.1644943792.git.andreyknvl@google.com [dan.carpenter@oracle.com: remove unnecessary check in alloc_thread_stack_node()] Link: https://lkml.kernel.org/r/20220301080706.GB17208@kili Link: https://lkml.kernel.org/r/698c5ab21743c796d46c15d075b9481825973e34.1643047180.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Signed-off-by: Dan Carpenter Acked-by: Catalin Marinas Acked-by: Marco Elver Reviewed-by: Marco Elver Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Evgenii Stepanov Cc: Mark Rutland Cc: Peter Collingbourne Cc: Vincenzo Frascino Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/fork.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) (limited to 'kernel') diff --git a/kernel/fork.c b/kernel/fork.c index ce0ffe48937f..9796897560ab 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -286,11 +286,13 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) if (!s) continue; - /* Mark stack accessible for KASAN. */ + /* Reset stack metadata. */ kasan_unpoison_range(s->addr, THREAD_SIZE); + stack = kasan_reset_tag(s->addr); + /* Clear stale pointers from reused stack. */ - memset(s->addr, 0, THREAD_SIZE); + memset(stack, 0, THREAD_SIZE); if (memcg_charge_kernel_stack(s)) { vfree(s->addr); @@ -298,7 +300,7 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) } tsk->stack_vm_area = s; - tsk->stack = s->addr; + tsk->stack = stack; return 0; } @@ -326,8 +328,7 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) * so cache the vm_struct. */ tsk->stack_vm_area = vm; - if (stack) - stack = kasan_reset_tag(stack); + stack = kasan_reset_tag(stack); tsk->stack = stack; return 0; } -- cgit v1.2.3 From 23689e91fb22c15b84ac6c22ad9942039792f3af Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Thu, 24 Mar 2022 18:11:32 -0700 Subject: kasan, vmalloc: add vmalloc tagging for HW_TAGS Add vmalloc tagging support to HW_TAGS KASAN. The key difference between HW_TAGS and the other two KASAN modes when it comes to vmalloc: HW_TAGS KASAN can only assign tags to physical memory. The other two modes have shadow memory covering every mapped virtual memory region. Make __kasan_unpoison_vmalloc() for HW_TAGS KASAN: - Skip non-VM_ALLOC mappings as HW_TAGS KASAN can only tag a single mapping of normal physical memory; see the comment in the function. - Generate a random tag, tag the returned pointer and the allocation, and initialize the allocation at the same time. - Propagate the tag into the page stucts to allow accesses through page_address(vmalloc_to_page()). The rest of vmalloc-related KASAN hooks are not needed: - The shadow-related ones are fully skipped. - __kasan_poison_vmalloc() is kept as a no-op with a comment. Poisoning and zeroing of physical pages that are backing vmalloc() allocations are skipped via __GFP_SKIP_KASAN_UNPOISON and __GFP_SKIP_ZERO: __kasan_unpoison_vmalloc() does that instead. Enabling CONFIG_KASAN_VMALLOC with HW_TAGS is not yet allowed. Link: https://lkml.kernel.org/r/d19b2e9e59a9abc59d05b72dea8429dcaea739c6.1643047180.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Co-developed-by: Vincenzo Frascino Signed-off-by: Vincenzo Frascino Acked-by: Marco Elver Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Catalin Marinas Cc: Dmitry Vyukov Cc: Evgenii Stepanov Cc: Mark Rutland Cc: Peter Collingbourne Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/scs.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/scs.c b/kernel/scs.c index 579841be8864..b83bc9251f99 100644 --- a/kernel/scs.c +++ b/kernel/scs.c @@ -32,7 +32,7 @@ static void *__scs_alloc(int node) for (i = 0; i < NR_CACHED_SCS; i++) { s = this_cpu_xchg(scs_cache[i], NULL); if (s) { - kasan_unpoison_vmalloc(s, SCS_SIZE); + kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_NONE); memset(s, 0, SCS_SIZE); return s; } @@ -78,7 +78,7 @@ void scs_free(void *s) if (this_cpu_cmpxchg(scs_cache[i], 0, s) == NULL) return; - kasan_unpoison_vmalloc(s, SCS_SIZE); + kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_NONE); vfree_atomic(s); } -- cgit v1.2.3 From f6e39794f4b6da7ca9b77f2f9ad11fd6f0ac83e5 Mon Sep 17 00:00:00 2001 From: Andrey Konovalov Date: Thu, 24 Mar 2022 18:11:35 -0700 Subject: kasan, vmalloc: only tag normal vmalloc allocations The kernel can use to allocate executable memory. The only supported way to do that is via __vmalloc_node_range() with the executable bit set in the prot argument. (vmap() resets the bit via pgprot_nx()). Once tag-based KASAN modes start tagging vmalloc allocations, executing code from such allocations will lead to the PC register getting a tag, which is not tolerated by the kernel. Only tag the allocations for normal kernel pages. [andreyknvl@google.com: pass KASAN_VMALLOC_PROT_NORMAL to kasan_unpoison_vmalloc()] Link: https://lkml.kernel.org/r/9230ca3d3e40ffca041c133a524191fd71969a8d.1646233925.git.andreyknvl@google.com [andreyknvl@google.com: support tagged vmalloc mappings] Link: https://lkml.kernel.org/r/2f6605e3a358cf64d73a05710cb3da356886ad29.1646233925.git.andreyknvl@google.com [andreyknvl@google.com: don't unintentionally disabled poisoning] Link: https://lkml.kernel.org/r/de4587d6a719232e83c760113e46ed2d4d8da61e.1646757322.git.andreyknvl@google.com Link: https://lkml.kernel.org/r/fbfd9939a4dc375923c9a5c6b9e7ab05c26b8c6b.1643047180.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov Acked-by: Marco Elver Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Catalin Marinas Cc: Dmitry Vyukov Cc: Evgenii Stepanov Cc: Mark Rutland Cc: Peter Collingbourne Cc: Vincenzo Frascino Cc: Will Deacon Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/scs.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) (limited to 'kernel') diff --git a/kernel/scs.c b/kernel/scs.c index b83bc9251f99..b7e1b096d906 100644 --- a/kernel/scs.c +++ b/kernel/scs.c @@ -32,15 +32,19 @@ static void *__scs_alloc(int node) for (i = 0; i < NR_CACHED_SCS; i++) { s = this_cpu_xchg(scs_cache[i], NULL); if (s) { - kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_NONE); + s = kasan_unpoison_vmalloc(s, SCS_SIZE, + KASAN_VMALLOC_PROT_NORMAL); memset(s, 0, SCS_SIZE); - return s; + goto out; } } - return __vmalloc_node_range(SCS_SIZE, 1, VMALLOC_START, VMALLOC_END, + s = __vmalloc_node_range(SCS_SIZE, 1, VMALLOC_START, VMALLOC_END, GFP_SCS, PAGE_KERNEL, 0, node, __builtin_return_address(0)); + +out: + return kasan_reset_tag(s); } void *scs_alloc(int node) @@ -78,7 +82,7 @@ void scs_free(void *s) if (this_cpu_cmpxchg(scs_cache[i], 0, s) == NULL) return; - kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_NONE); + kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_PROT_NORMAL); vfree_atomic(s); } -- cgit v1.2.3