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=6cb6102a0a7b0c52060753dd62d070a1d1e7134... 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; 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; }
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=6cb6102a0a7b0c52060753dd62d070a1d1e7134... 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")
linux-stable-mirror@lists.linaro.org
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Sean Christopherson -
Tadeusz Struk