On 03/08/21 15:55, Ovidiu Panait wrote:
From: Nicholas Piggin npiggin@gmail.com
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: Ovidiu Panait ovidiu.panait@windriver.com
virt/kvm/kvm_main.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 4e23d0b4b810..469361d01116 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1485,6 +1485,13 @@ 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,
@@ -1534,13 +1541,21 @@ 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; }
/*
Acked-by: Paolo Bonzini pbonzini@redhat.com