diff options
| author | Nicholas Piggin <npiggin@gmail.com> | 2021-06-24 08:29:04 -0400 |
|---|---|---|
| committer | Sasha Levin <sashal@kernel.org> | 2021-06-30 08:47:25 -0400 |
| commit | dd8ed6c9bc2224c1ace5292d01089d3feb7ebbc3 (patch) | |
| tree | a7082bc79c2d1392184e44ca3d142656a35141af /virt | |
| parent | 5fd0c2cf7b11c23aebbbc512cfed08485f0a422a (diff) | |
KVM: do not allow mapping valid but non-reference-counted pages
commit f8be156be163a052a067306417cd0ff679068c97 upstream.
It's possible to create a region which maps valid but non-refcounted
pages (e.g., tail pages of non-compound higher order allocations). These
host pages can then be returned by gfn_to_page, gfn_to_pfn, etc., family
of APIs, which take a reference to the page, which takes it from 0 to 1.
When the reference is dropped, this will free the page incorrectly.
Fix this by only taking a reference on valid pages if it was non-zero,
which indicates it is participating in normal refcounting (and can be
released with put_page).
This addresses CVE-2021-22543.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index f446c36f5800..1353439691cf 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1883,6 +1883,13 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault) return true; } +static int kvm_try_get_pfn(kvm_pfn_t pfn) +{ + if (kvm_is_reserved_pfn(pfn)) + return 1; + return get_page_unless_zero(pfn_to_page(pfn)); +} + static int hva_to_pfn_remapped(struct vm_area_struct *vma, unsigned long addr, bool *async, bool write_fault, bool *writable, @@ -1932,13 +1939,21 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma, * Whoever called remap_pfn_range is also going to call e.g. * unmap_mapping_range before the underlying pages are freed, * causing a call to our MMU notifier. + * + * Certain IO or PFNMAP mappings can be backed with valid + * struct pages, but be allocated without refcounting e.g., + * tail pages of non-compound higher order allocations, which + * would then underflow the refcount when the caller does the + * required put_page. Don't allow those pages here. */ - kvm_get_pfn(pfn); + if (!kvm_try_get_pfn(pfn)) + r = -EFAULT; out: pte_unmap_unlock(ptep, ptl); *p_pfn = pfn; - return 0; + + return r; } /* |