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: x86@kernel.org Cc: "H. Peter Anvin" hpa@zytor.com 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 5b5bdac97c7b..d25b72d7b1b1 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 1/24/22 18:26, 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.
access_ok only checks that the pointer is in the userspace range. Is this correct? And if so, what are the exact circumstances in which access_ok returns a non-NULL but also non-userspace address?
Thanks,
Paolo
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: x86@kernel.org Cc: "H. Peter Anvin" hpa@zytor.com 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 5b5bdac97c7b..d25b72d7b1b1 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 Mon, Jan 24, 2022, Paolo Bonzini wrote:
On 1/24/22 18:26, 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.
access_ok only checks that the pointer is in the userspace range. Is this correct? And if so, what are the exact circumstances in which access_ok returns a non-NULL but also non-userspace address?
I "objected" to this patch in its initial posting[*]. AFAICT adding access_ok() is just masking a more egregious bug where interpretation of vm_pgoff as a PFN base is flat out wrong except for select backing stores that use VM_PFNMAP. In other words, the vm_pgoff hack works for the /dev/mem use case, but it is wrong in general.
[*] https://lore.kernel.org/all/Ybp0naX%2FZTG9FNEa@google.com
Thanks,
Paolo
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: x86@kernel.org Cc: "H. Peter Anvin" hpa@zytor.com 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 5b5bdac97c7b..d25b72d7b1b1 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 1/24/22 10:29, Sean Christopherson wrote:
On Mon, Jan 24, 2022, Paolo Bonzini wrote:
On 1/24/22 18:26, 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.
access_ok only checks that the pointer is in the userspace range. Is this correct? And if so, what are the exact circumstances in which access_ok returns a non-NULL but also non-userspace address?
I "objected" to this patch in its initial posting[*]. AFAICT adding access_ok() is just masking a more egregious bug where interpretation of vm_pgoff as a PFN base is flat out wrong except for select backing stores that use VM_PFNMAP. In other words, the vm_pgoff hack works for the /dev/mem use case, but it is wrong in general.
The issue here is not related to /dev/mem, but binder allocated memory, which is yet another special mapping use case. In this case the condition
if (!vma || !(vma->vm_flags & VM_PFNMAP))
doesn't cover this special mappings. Adding the access_ok() was my something that fixed the use-after-free issue for me, and since I didn't have anything better I thought I will send an RFC to start some discussion. After some more debugging I came up with the bellow. Will that be more acceptable?
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h index 5b5bdac97c7b..0f03e5401a98 100644 --- a/arch/x86/kvm/mmu/paging_tmpl.h +++ b/arch/x86/kvm/mmu/paging_tmpl.h @@ -167,7 +167,7 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
mmap_read_lock(current->mm); vma = find_vma_intersection(current->mm, vaddr, vaddr + PAGE_SIZE); - if (!vma || !(vma->vm_flags & VM_PFNMAP)) { + if (!vma || !(vma->vm_flags & VM_MIXEDMAP)) { mmap_read_unlock(current->mm); return -EFAULT; }
On Mon, Jan 24, 2022, Tadeusz Struk wrote:
On 1/24/22 10:29, Sean Christopherson wrote:
On Mon, Jan 24, 2022, Paolo Bonzini wrote:
On 1/24/22 18:26, 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.
access_ok only checks that the pointer is in the userspace range. Is this correct? And if so, what are the exact circumstances in which access_ok returns a non-NULL but also non-userspace address?
I "objected" to this patch in its initial posting[*]. AFAICT adding access_ok() is just masking a more egregious bug where interpretation of vm_pgoff as a PFN base is flat out wrong except for select backing stores that use VM_PFNMAP. In other words, the vm_pgoff hack works for the /dev/mem use case, but it is wrong in general.
The issue here is not related to /dev/mem, but binder allocated memory, which is yet another special mapping use case. In this case the condition
if (!vma || !(vma->vm_flags & VM_PFNMAP))
doesn't cover this special mappings. Adding the access_ok() was my something that fixed the use-after-free issue for me, and since I didn't have anything better I thought I will send an RFC to start some discussion. After some more debugging I came up with the bellow. Will that be more acceptable?
I'm pretty sure anything that keeps the vm_pgoff "logic" is a band-aid. But I'm 99% sure we can simply do cmpxchg directly on the user address, we just need to get support for that, which has happily been posted[*]. I'll give that a shot tomorrow, I want to convert similar code in the emulator, it'd be very nice to purge all of this crud.
[*] https://lore.kernel.org/all/20220120160822.852009966@infradead.org
On Tue, Jan 25, 2022, Sean Christopherson wrote:
On Mon, Jan 24, 2022, Tadeusz Struk wrote:
On 1/24/22 10:29, Sean Christopherson wrote:
On Mon, Jan 24, 2022, Paolo Bonzini wrote:
On 1/24/22 18:26, 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.
access_ok only checks that the pointer is in the userspace range. Is this correct? And if so, what are the exact circumstances in which access_ok returns a non-NULL but also non-userspace address?
I "objected" to this patch in its initial posting[*]. AFAICT adding access_ok() is just masking a more egregious bug where interpretation of vm_pgoff as a PFN base is flat out wrong except for select backing stores that use VM_PFNMAP. In other words, the vm_pgoff hack works for the /dev/mem use case, but it is wrong in general.
The issue here is not related to /dev/mem, but binder allocated memory, which is yet another special mapping use case. In this case the condition
if (!vma || !(vma->vm_flags & VM_PFNMAP))
doesn't cover this special mappings. Adding the access_ok() was my something that fixed the use-after-free issue for me, and since I didn't have anything better I thought I will send an RFC to start some discussion. After some more debugging I came up with the bellow. Will that be more acceptable?
I'm pretty sure anything that keeps the vm_pgoff "logic" is a band-aid. But I'm 99% sure we can simply do cmpxchg directly on the user address, we just need to get support for that, which has happily been posted[*]. I'll give that a shot tomorrow, I want to convert similar code in the emulator, it'd be very nice to purge all of this crud.
[*] https://lore.kernel.org/all/20220120160822.852009966@infradead.org
Posted a series and belatedly realized my script didn't pick up Debugged-by: to Cc you :-/ Let me know if you want me to forward any/all of the series to you.
https://lore.kernel.org/all/20220201010838.1494405-1-seanjc@google.com
On 1/31/22 17:11, Sean Christopherson wrote:
On Tue, Jan 25, 2022, Sean Christopherson wrote:
On Mon, Jan 24, 2022, Tadeusz Struk wrote:
On 1/24/22 10:29, Sean Christopherson wrote:
On Mon, Jan 24, 2022, Paolo Bonzini wrote:
On 1/24/22 18:26, 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.
access_ok only checks that the pointer is in the userspace range. Is this correct? And if so, what are the exact circumstances in which access_ok returns a non-NULL but also non-userspace address?
I "objected" to this patch in its initial posting[*]. AFAICT adding access_ok() is just masking a more egregious bug where interpretation of vm_pgoff as a PFN base is flat out wrong except for select backing stores that use VM_PFNMAP. In other words, the vm_pgoff hack works for the /dev/mem use case, but it is wrong in general.
The issue here is not related to /dev/mem, but binder allocated memory, which is yet another special mapping use case. In this case the condition
if (!vma || !(vma->vm_flags & VM_PFNMAP))
doesn't cover this special mappings. Adding the access_ok() was my something that fixed the use-after-free issue for me, and since I didn't have anything better I thought I will send an RFC to start some discussion. After some more debugging I came up with the bellow. Will that be more acceptable?
I'm pretty sure anything that keeps the vm_pgoff "logic" is a band-aid. But I'm 99% sure we can simply do cmpxchg directly on the user address, we just need to get support for that, which has happily been posted[*]. I'll give that a shot tomorrow, I want to convert similar code in the emulator, it'd be very nice to purge all of this crud.
[*] https://lore.kernel.org/all/20220120160822.852009966@infradead.org
Posted a series and belatedly realized my script didn't pick up Debugged-by: to Cc you :-/ Let me know if you want me to forward any/all of the series to you.
https://lore.kernel.org/all/20220201010838.1494405-1-seanjc@google.com
It's fine, I can follow up using the link you sent. I will try it tomorrow and let you know.
linux-stable-mirror@lists.linaro.org
-
Paolo Bonzini -
Sean Christopherson -
Tadeusz Struk