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KVM: do not allow mapping valid but non-reference-counted pages

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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>
This commit is contained in:
Nicholas Piggin 2021-06-24 08:29:04 -04:00 committed by Paolo Bonzini
parent 309505dd56
commit f8be156be1
1 changed files with 17 additions and 2 deletions
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19
virt/kvm/kvm_main.c
View File

@ -2055,6 +2055,13 @@ 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,
@ -2104,13 +2111,21 @@ 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;
}
/*