Re: [PATCH v1] KVM: arm64: Fix benign bug with incorrect use of VA_BITS.
On Mon, 5 Dec 2022 11:40:31 +, Ryan Roberts wrote: > get_user_mapping_size() uses kvm's pgtable library to walk a user space > page table created by the kernel, and in doing so, fakes up the metadata > that the library needs, including ia_bits, which defines the size of the > input address. > > For the case where the kernel is compiled for 52 VA bits but runs on HW > that does not support LVA, it will fall back to 48 VA bits at runtime. > Therefore we must use vabits_actual rather than VA_BITS to get the true > address size. > > [...] Applied to next, thanks! [1/1] KVM: arm64: Fix benign bug with incorrect use of VA_BITS. commit: 219072c09abde0f1d0a6ce091be375e8eb7d08f0 Cheers, M. -- Without deviation from the norm, progress is not possible. ___ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
Re: [PATCH v1] KVM: arm64: Fix benign bug with incorrect use of VA_BITS.
On 05/12/2022 13:49, Marc Zyngier wrote: > Hi Ryan, > > Thanks for that. > > On Mon, 05 Dec 2022 11:40:31 +, > Ryan Roberts wrote: >> >> get_user_mapping_size() uses kvm's pgtable library to walk a user space >> page table created by the kernel, and in doing so, fakes up the metadata >> that the library needs, including ia_bits, which defines the size of the >> input address. > > It isn't supposed to "fake" anything. It simply provides the > information that the walker needs to correctly parse the page tables. Apologies - poor choice of words. > >> >> For the case where the kernel is compiled for 52 VA bits but runs on HW >> that does not support LVA, it will fall back to 48 VA bits at runtime. >> Therefore we must use vabits_actual rather than VA_BITS to get the true >> address size. >> >> This is benign in the current code base because the pgtable library only >> uses it for error checking. >> >> Fixes: 6011cf68c885 ("KVM: arm64: Walk userspace page tables to compute >> the THP mapping size") > > nit: this should appear on a single line, without a line-break in the > middle [1]...> >> > > ... without a blank line between Fixes: and the rest of the tags. Ahh, thanks for the pointer. I'll admit that checkpatch did raise this but I assumed it was a false positive, because assumed the 75 chars per line rule would override. > > And while I'm on the "trivial remarks" train, drop the full stop at > the end of the subject line. Yep, will do. > >> Signed-off-by: Ryan Roberts >> --- >> arch/arm64/kvm/mmu.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >> index 4efb983cff43..1ef0704420d9 100644 >> --- a/arch/arm64/kvm/mmu.c >> +++ b/arch/arm64/kvm/mmu.c >> @@ -641,7 +641,7 @@ static int get_user_mapping_size(struct kvm *kvm, u64 >> addr) >> { >> struct kvm_pgtable pgt = { >> .pgd= (kvm_pte_t *)kvm->mm->pgd, >> -.ia_bits= VA_BITS, >> +.ia_bits= vabits_actual, >> .start_level= (KVM_PGTABLE_MAX_LEVELS - >> CONFIG_PGTABLE_LEVELS), >> .mm_ops = &kvm_user_mm_ops, >> -- >> 2.25.1 >> >> > > Other than the above nits, this is well spotted. I need to regenerate > the kvmarm/next branch after the sysreg attack from James, so I'll try > and fold that in. Sounds like you are happy to tend to the nits and don't need me to repost? > > Thanks, > > M. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst#n139 > ___ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
Re: [PATCH v1] KVM: arm64: Fix benign bug with incorrect use of VA_BITS.
Hi Ryan, Thanks for that. On Mon, 05 Dec 2022 11:40:31 +, Ryan Roberts wrote: > > get_user_mapping_size() uses kvm's pgtable library to walk a user space > page table created by the kernel, and in doing so, fakes up the metadata > that the library needs, including ia_bits, which defines the size of the > input address. It isn't supposed to "fake" anything. It simply provides the information that the walker needs to correctly parse the page tables. > > For the case where the kernel is compiled for 52 VA bits but runs on HW > that does not support LVA, it will fall back to 48 VA bits at runtime. > Therefore we must use vabits_actual rather than VA_BITS to get the true > address size. > > This is benign in the current code base because the pgtable library only > uses it for error checking. > > Fixes: 6011cf68c885 ("KVM: arm64: Walk userspace page tables to compute > the THP mapping size") nit: this should appear on a single line, without a line-break in the middle [1]... > ... without a blank line between Fixes: and the rest of the tags. And while I'm on the "trivial remarks" train, drop the full stop at the end of the subject line. > Signed-off-by: Ryan Roberts > --- > arch/arm64/kvm/mmu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 4efb983cff43..1ef0704420d9 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -641,7 +641,7 @@ static int get_user_mapping_size(struct kvm *kvm, u64 > addr) > { > struct kvm_pgtable pgt = { > .pgd= (kvm_pte_t *)kvm->mm->pgd, > - .ia_bits= VA_BITS, > + .ia_bits= vabits_actual, > .start_level= (KVM_PGTABLE_MAX_LEVELS - > CONFIG_PGTABLE_LEVELS), > .mm_ops = &kvm_user_mm_ops, > -- > 2.25.1 > > Other than the above nits, this is well spotted. I need to regenerate the kvmarm/next branch after the sysreg attack from James, so I'll try and fold that in. Thanks, M. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst#n139 -- Without deviation from the norm, progress is not possible. ___ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm