Re: [PATCH 2/5 v4] KVM: nSVM: Check addresses of MSR and IO permission maps

Sean Christopherson
2021-03-24T19:16:45Z

On Wed, Mar 24, 2021, Krish Sadhukhan wrote:
> According to section "Canonicalization and Consistency Checks" in APM vol 2,
> the following guest state is illegal:
>
> "The MSR or IOIO intercept tables extend to a physical address that
> is greater than or equal to the maximum supported physical address."
>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
> ---
> arch/x86/kvm/svm/nested.c | 28 +++++++++++++++++++++-------
> 1 file changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 35891d9a1099..b08d1c595736 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -231,7 +231,15 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
> return true;
> }
>
> -static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
> +static bool nested_svm_check_bitmap_pa(struct kvm_vcpu *vcpu, u64 pa,
> + u8 order)
> +{
> + u64 last_pa = PAGE_ALIGN(pa) + (PAGE_SIZE << order) - 1;

Ugh, I really wish things that "must" happen were actually enforced by hardware.

The MSRPM must be aligned on a 4KB boundary... The VMRUN instruction ignores
the lower 12 bits of the address specified in the VMCB.

So, ignoring an unaligned @pa is correct, but that means
nested_svm_exit_handled_msr() and nested_svm_intercept_ioio() are busted.

> + return last_pa > pa && !(last_pa >> cpuid_maxphyaddr(vcpu));

Please use kvm_vcpu_is_legal_gpa().

> +}
> +
> +static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
> + struct vmcb_control_area *control)
> {
> if ((vmcb_is_intercept(control, INTERCEPT_VMRUN)) == 0)
> return false;
> @@ -243,12 +251,18 @@ static bool nested_vmcb_check_controls(struct vmcb_control_area *control)
> !npt_enabled)
> return false;
>
> + if (!nested_svm_check_bitmap_pa(vcpu, control->msrpm_base_pa,
> + MSRPM_ALLOC_ORDER))
> + return false;
> + if (!nested_svm_check_bitmap_pa(vcpu, control->iopm_base_pa,
> + IOPM_ALLOC_ORDER))

I strongly dislike using the alloc orders, relying on kernel behavior to
represent architectural values it sketchy. Case in point, IOPM_ALLOC_ORDER is a
16kb size, whereas the actual size of the IOPM is 12kb. I also called this out
in v1...

https://lkml.kernel.org/r/YAd9MBkpDjC1MY6E@google.com

> + return false;
> +
> return true;
> }
>
> -static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12)
> +static bool nested_vmcb_checks(struct kvm_vcpu *vcpu, struct vmcb *vmcb12)
> {
> - struct kvm_vcpu *vcpu = &svm->vcpu;
> bool vmcb12_lma;
>
> if ((vmcb12->save.efer & EFER_SVME) == 0)
> @@ -268,10 +282,10 @@ static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12)
> kvm_vcpu_is_illegal_gpa(vcpu, vmcb12->save.cr3))
> return false;
> }
> - if (!kvm_is_valid_cr4(&svm->vcpu, vmcb12->save.cr4))
> + if (!kvm_is_valid_cr4(vcpu, vmcb12->save.cr4))
> return false;
>
> - return nested_vmcb_check_controls(&vmcb12->control);
> + return nested_vmcb_check_controls(vcpu, &vmcb12->control);
> }
>
> static void load_nested_vmcb_control(struct vcpu_svm *svm,
> @@ -515,7 +529,7 @@ int nested_svm_vmrun(struct vcpu_svm *svm)
> if (WARN_ON_ONCE(!svm->nested.initialized))
> return -EINVAL;
>
> - if (!nested_vmcb_checks(svm, vmcb12)) {
> + if (!nested_vmcb_checks(&svm->vcpu, vmcb12)) {

Please use @vcpu directly. Looks like this needs a rebase, as the prototype for
nested_svm_vmrun() is wrong relative to kvm/queue.

> vmcb12->control.exit_code = SVM_EXIT_ERR;
> vmcb12->control.exit_code_hi = 0;
> vmcb12->control.exit_info_1 = 0;
> @@ -1191,7 +1205,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
> goto out_free;
>
> ret = -EINVAL;
> - if (!nested_vmcb_check_controls(ctl))
> + if (!nested_vmcb_check_controls(vcpu, ctl))
> goto out_free;
>
> /*
> --
> 2.27.0
>