[PATCH v3 2/8] KVM: x86: nSVM: Cache and validate vmcb12 g_pat

[Jim Mattson]

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 <jmatt...@google.com>
---
 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;
+
        bool initialized;
 
        /*
-- 
2.53.0.rc2.204.g2597b5adb4-goog