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

[Jim Mattson]

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 <jmatt...@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