Re: [PATCH 2/5 v6] nSVM: Check addresses of MSR and IO permission maps

Sean Christopherson
2021-04-02T17:45:41Z

On Thu, Apr 01, 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 | 23 +++++++++++++++++++----
> 1 file changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index fb204eaa8bb3..b3988b3a3fd5 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,
> + u32 size)

No need to put "u32 size)" on a separate line.

> +{
> + u64 last_pa = PAGE_ALIGN(pa) + size - 1;

Space between declaration and code. A comment about the silliness of hardware
silently ignoring bits 11:0 would also be nice.

> + return (kvm_vcpu_is_legal_gpa(vcpu, last_pa));

This fails to handle the case where "pa == -1", as the above will wrap to a
legal address and generate a false negative.

/* blah blah blah */
pa = PAGE_ALIGN(pa);
return kvm_vcpu_is_legal_gpa(pa) &&
kvm_vcpu_is_legal_gpa(pa + size - 1);

> +}
> +
> +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;
> @@ -243,6 +251,13 @@ 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_SIZE))
> + return false;
> + if (!nested_svm_check_bitmap_pa(vcpu, control->iopm_base_pa,
> + IOPM_ALLOC_SIZE - PAGE_SIZE + 1))

Align with the function's paranthesis, not the if statements, for both.

if (!nested_svm_check_bitmap_pa(vcpu, control->iopm_base_pa,
IOPM_ALLOC_SIZE - PAGE_SIZE + 1))
> + return false;
> +
> return true;
> }
>
> @@ -275,7 +290,7 @@ static bool nested_vmcb_check_save(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 true;
> @@ -531,7 +546,7 @@ int nested_svm_vmrun(struct vcpu_svm *svm)
> load_nested_vmcb_control(svm, &vmcb12->control);
>
> if (!nested_vmcb_check_save(svm, vmcb12) ||
> - !nested_vmcb_check_controls(&svm->nested.ctl)) {
> + !nested_vmcb_check_controls(&svm->vcpu, &svm->nested.ctl)) {

Pass "vcpu" directly (probably only once you rebase).

> vmcb12->control.exit_code = SVM_EXIT_ERR;
> vmcb12->control.exit_code_hi = 0;
> vmcb12->control.exit_info_1 = 0;
> @@ -1207,7 +1222,7 @@ 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
>