| Message ID | 20211214232039.851405-1-tadeusz.struk@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [RFC] KVM: x86/mmu: fix UAF in paging_update_accessed_dirty_bits | expand |
On Tue, Dec 14, 2021, Tadeusz Struk wrote: > Syzbot reported an use-after-free bug in update_accessed_dirty_bits(). > Fix this by checking if the memremap'ed pointer is still valid. ... > Fixes: bd53cb35a3e9 ("X86/KVM: Handle PFNs outside of kernel reach when touching GPTEs") > Link: https://syzkaller.appspot.com/bug?id=6cb6102a0a7b0c52060753dd62d070a1d1e71347 > Reported-by: syzbot+6cde2282daa792c49ab8@syzkaller.appspotmail.com > Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org> > --- > arch/x86/kvm/mmu/paging_tmpl.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h > index 708a5d297fe1..5cf4815d1c45 100644 > --- a/arch/x86/kvm/mmu/paging_tmpl.h > +++ b/arch/x86/kvm/mmu/paging_tmpl.h > @@ -174,7 +174,7 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, > pfn = ((vaddr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; Isn't this code flat out wrong? vm_pgoff is usually the offset relative to the file and has nothing to do with the pfn. I see that remap_pfn_range_notrack() stuffs "vma->vm_pgoff = pfn", but that's a weird quirk of that particular usage of VM_PFNMAP that I'm guessing happened to align with the original usage of this mess. But unless there's magic I'm missing, vm_pgoff is not guaranteed to have any relation to the pfn for any ol' VM_PFNMAP vma. In other words, I suspect pfn and paddr are complete garbage, and adding the access_ok() check masks that. > paddr = pfn << PAGE_SHIFT; > table = memremap(paddr, PAGE_SIZE, MEMREMAP_WB); > - if (!table) { > + if (!table || !access_ok(table, PAGE_SIZE)) { > mmap_read_unlock(current->mm); > return -EFAULT; > } > -- > 2.33.1 >
On 12/15/21 15:05, Sean Christopherson wrote: >> @@ -174,7 +174,7 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, >> pfn = ((vaddr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; > Isn't this code flat out wrong? vm_pgoff is usually the offset relative to the > file and has nothing to do with the pfn. I see that remap_pfn_range_notrack() > stuffs "vma->vm_pgoff = pfn", but that's a weird quirk of that particular usage > of VM_PFNMAP that I'm guessing happened to align with the original usage of this > mess. But unless there's magic I'm missing, vm_pgoff is not guaranteed to have > any relation to the pfn for any ol' VM_PFNMAP vma. > > In other words, I suspect pfn and paddr are complete garbage, and adding the > access_ok() check masks that. > The answer to your question might be in the commit message of the original commit that added this code: bd53cb35a3e9 ("X86/KVM: Handle PFNs outside of kernel reach when touching GPTEs")
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index 708a5d297fe1..5cf4815d1c45 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -174,7 +174,7 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, pfn = ((vaddr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; paddr = pfn << PAGE_SHIFT; table = memremap(paddr, PAGE_SIZE, MEMREMAP_WB); - if (!table) { + if (!table || !access_ok(table, PAGE_SIZE)) { mmap_read_unlock(current->mm); return -EFAULT; }
Syzbot reported an use-after-free bug in update_accessed_dirty_bits(). Fix this by checking if the memremap'ed pointer is still valid. Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Sean Christopherson <seanjc@google.com> Cc: Vitaly Kuznetsov <vkuznets@redhat.com> Cc: Wanpeng Li <wanpengli@tencent.com> Cc: Jim Mattson <jmattson@google.com> Cc: Joerg Roedel <joro@8bytes.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: <x86@kernel.org> Cc: <kvm@vger.kernel.org> Cc: <stable@vger.kernel.org> Fixes: bd53cb35a3e9 ("X86/KVM: Handle PFNs outside of kernel reach when touching GPTEs") Link: https://syzkaller.appspot.com/bug?id=6cb6102a0a7b0c52060753dd62d070a1d1e71347 Reported-by: syzbot+6cde2282daa792c49ab8@syzkaller.appspotmail.com Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org> --- arch/x86/kvm/mmu/paging_tmpl.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)