[PATCH v2 05/13] KVM: nSVM: Add missing consistency check for EFER, CR0, CR4, and CS

Yosry Ahmed
2025-11-10T22:29:52Z

According to the APM Volume #2, 15.5, Canonicalization and Consistency
Checks (24593—Rev. 3.42—March 2024), the following condition (among
others) results in a #VMEXIT with VMEXIT_INVALID (aka SVM_EXIT_ERR):

EFER.LME, CR0.PG, CR4.PAE, CS.L, and CS.D are all non-zero.

Add the missing consistency check. This is functionally a nop because
the nested VMRUN results in SVM_EXIT_ERR in HW, which is forwarded to
L1, but KVM makes all consistency checks before a VMRUN is actually
attempted.

Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
---
arch/x86/kvm/svm/nested.c | 7 +++++++
arch/x86/kvm/svm/svm.h | 1 +
2 files changed, 8 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 87bcc5eff96e8..abdaacb04dd9e 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -380,6 +380,11 @@ static bool __nested_vmcb_check_save(struct kvm_vcpu *vcpu,
CC(!(save->cr0 & X86_CR0_PE)) ||
CC(!kvm_vcpu_is_legal_cr3(vcpu, save->cr3)))
return false;
+
+ if (CC((save->cr4 & X86_CR4_PAE) &&
+ (save->cs.attrib & SVM_SELECTOR_L_MASK) &&
+ (save->cs.attrib & SVM_SELECTOR_DB_MASK)))
+ return false;
}

/* Note, SVM doesn't have any additional restrictions on CR4. */
@@ -473,6 +478,8 @@ static void __nested_copy_vmcb_save_to_cache(struct vmcb_save_area_cached *to,
* Copy only fields that are validated, as we need them
* to avoid TOC/TOU races.
*/
+ to->cs = from->cs;
+
to->efer = from->efer;
to->cr0 = from->cr0;
to->cr3 = from->cr3;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 3e805a43ffcdb..a6913a0820125 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -142,6 +142,7 @@ struct kvm_vmcb_info {
};

struct vmcb_save_area_cached {
+ struct vmcb_seg cs;
u64 efer;
u64 cr4;
u64 cr3;
--
2.51.2.1041.gc1ab5b90ca-goog