[PATCH v4 2/8] KVM: x86: nSVM: Cache and validate vmcb12 g_pat

[Jim Mattson <jmattson@google.com>]

Cache g_pat from vmcb12 in vmcb_save_area_cached to avoid TOCTTOU issues,
and add a validity check so that when nested paging is enabled for vmcb12,
an invalid g_pat at emulated VMRUN 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 <jmattson@google.com>
---
 arch/x86/kvm/svm/nested.c | 17 +++++++++++++----
 arch/x86/kvm/svm/svm.h    |  1 +
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index b72a1f3c4144..91b35adb83f8 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -426,7 +426,8 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
 
 /* Common checks that apply to both L1 and L2 state.  */
 static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu,
-				   struct vmcb_save_area_cached *save)
+				   struct vmcb_save_area_cached *save,
+				   bool check_gpat)
 {
 	if (CC(!(save->efer & EFER_SVME)))
 		return false;
@@ -462,6 +463,9 @@ static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu,
 	if (CC(!kvm_valid_efer(vcpu, save->efer)))
 		return false;
 
+	if (check_gpat && CC(!kvm_pat_valid(save->g_pat)))
+		return false;
+
 	return true;
 }
 
@@ -573,6 +577,7 @@ static void __nested_copy_vmcb_save_to_cache(struct vmcb_save_area_cached *to,
 
 	to->rax = from->rax;
 	to->cr2 = from->cr2;
+	to->g_pat = from->g_pat;
 
 	svm_copy_lbrs(to, from);
 }
@@ -1036,7 +1041,8 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa, bool from_vmrun)
 
 	enter_guest_mode(vcpu);
 
-	if (!nested_vmcb_check_save(vcpu, &svm->nested.save) ||
+	if (!nested_vmcb_check_save(vcpu, &svm->nested.save,
+				    nested_npt_enabled(svm)) ||
 	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl,
 					svm->vmcb01.ptr->save.cr0))
 		return -EINVAL;
@@ -2006,13 +2012,16 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 
 	/*
 	 * Validate host state saved from before VMRUN (see
-	 * nested_svm_check_permissions).
+	 * nested_svm_check_permissions). Note that the g_pat field is not
+	 * validated, because (a) it may have been clobbered by SMM before
+	 * KVM_GET_NESTED_STATE, and (b) it is not loaded at emulated
+	 * #VMEXIT.
 	 */
 	__nested_copy_vmcb_save_to_cache(&save_cached, save);
 	if (!(save->cr0 & X86_CR0_PG) ||
 	    !(save->cr0 & X86_CR0_PE) ||
 	    (save->rflags & X86_EFLAGS_VM) ||
-	    !nested_vmcb_check_save(vcpu, &save_cached))
+	    !nested_vmcb_check_save(vcpu, &save_cached, false))
 		goto out_free;
 
 
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 9850ed01e16e..a49c48459e0b 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -161,6 +161,7 @@ struct vmcb_save_area_cached {
 	u64 isst_addr;
 	u64 rax;
 	u64 cr2;
+	u64 g_pat;
 	u64 dbgctl;
 	u64 br_from;
 	u64 br_to;
-- 
2.53.0.239.g8d8fc8a987-goog