| Message ID | 20210803135521.2603575-2-ovidiu.panait@windriver.com |
|---|---|
| State | New |
| Headers | show |
| Series | [4.14,1/3] KVM: do not assume PTE is writable after follow_pfn | expand |
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>
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; } /*