On Thu, Feb 05, 2026, Jim Mattson wrote:
> Cache g_pat from vmcb12 in svm->nested.gpat to avoid TOCTTOU issues, and
> add a validity check so that when nested paging is enabled for vmcb12, an
> invalid g_pat causes an immediate VMEXIT with exit code VMEXIT_INVALID, as
> specified in the APM, volume 2: "Nested Paging and VMRUN/VMEXIT."
>
> Fixes: 3d6368ef580a ("KVM: SVM: Add VMRUN handler")
> Signed-off-by: Jim Mattson <[email protected]>
> ---
> arch/x86/kvm/svm/nested.c | 4 +++-
> arch/x86/kvm/svm/svm.h | 3 +++
> 2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index f72dbd10dcad..1d4ff6408b34 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -1027,9 +1027,11 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
>
> nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
> nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
> + svm->nested.gpat = vmcb12->save.g_pat;
>
> if (!nested_vmcb_check_save(vcpu) ||
> - !nested_vmcb_check_controls(vcpu)) {
> + !nested_vmcb_check_controls(vcpu) ||
> + (nested_npt_enabled(svm) && !kvm_pat_valid(svm->nested.gpat))) {
> vmcb12->control.exit_code = SVM_EXIT_ERR;
> vmcb12->control.exit_info_1 = 0;
> vmcb12->control.exit_info_2 = 0;
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 986d90f2d4ca..42a4bf83b3aa 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -208,6 +208,9 @@ struct svm_nested_state {
> */
> struct vmcb_save_area_cached save;
>
> + /* Cached guest PAT from vmcb12.save.g_pat */
> + u64 gpat;
Shouldn't this go in vmcb_save_area_cached?
> +
> bool initialized;
>
> /*
> --
> 2.53.0.rc2.204.g2597b5adb4-goog
>
