Message ID | 20220124172633.103323-1-tadeusz.struk@linaro.org (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [RESEND] KVM: x86/mmu: fix UAF in paging_update_accessed_dirty_bits | expand |
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=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 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=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 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.
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; }
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=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(-)