From: Sean Christopherson <seanjc@google.com> stable inclusion from stable-v6.6.130 commit 816fa1dfae4532e851b1fe6b2434c753ecbd86c7 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/15045 CVE: CVE-2026-43483 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 87d0f901a9bd8ae6be57249c737f20ac0cace93d ] Explicitly set/clear CR8 write interception when AVIC is (de)activated to fix a bug where KVM leaves the interception enabled after AVIC is activated. E.g. if KVM emulates INIT=>WFS while AVIC is deactivated, CR8 will remain intercepted in perpetuity. On its own, the dangling CR8 intercept is "just" a performance issue, but combined with the TPR sync bug fixed by commit d02e48830e3f ("KVM: SVM: Sync TPR from LAPIC into VMCB::V_TPR even if AVIC is active"), the danging intercept is fatal to Windows guests as the TPR seen by hardware gets wildly out of sync with reality. Note, VMX isn't affected by the bug as TPR_THRESHOLD is explicitly ignored when Virtual Interrupt Delivery is enabled, i.e. when APICv is active in KVM's world. I.e. there's no need to trigger update_cr8_intercept(), this is firmly an SVM implementation flaw/detail. WARN if KVM gets a CR8 write #VMEXIT while AVIC is active, as KVM should never enter the guest with AVIC enabled and CR8 writes intercepted. Fixes: 3bbf3565f48c ("svm: Do not intercept CR8 when enable AVIC") Cc: stable@vger.kernel.org Cc: Jim Mattson <jmattson@google.com> Cc: Naveen N Rao (AMD) <naveen@kernel.org> Cc: Maciej S. Szmigiero <maciej.szmigiero@oracle.com> Reviewed-by: Naveen N Rao (AMD) <naveen@kernel.org> Reviewed-by: Jim Mattson <jmattson@google.com> Link: https://patch.msgid.link/20260203190711.458413-3-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com> [Squash fix to avic_deactivate_vmcb. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> conflict: arch/x86/kvm/svm/avic.c [Conflict conflicts.] Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com> --- arch/x86/kvm/svm/avic.c | 6 +++++- arch/x86/kvm/svm/svm.c | 7 ++++--- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c index 6970b11a6b4c..5d4d1d2ebba9 100644 --- a/arch/x86/kvm/svm/avic.c +++ b/arch/x86/kvm/svm/avic.c @@ -88,9 +88,10 @@ static void avic_activate_vmcb(struct vcpu_svm *svm) vmcb->control.int_ctl &= ~(AVIC_ENABLE_MASK | X2APIC_MODE_MASK); vmcb->control.avic_physical_id &= ~AVIC_PHYSICAL_MAX_INDEX_MASK; - vmcb->control.int_ctl |= AVIC_ENABLE_MASK; + svm_clr_intercept(svm, INTERCEPT_CR8_WRITE); + /* * Note: KVM supports hybrid-AVIC mode, where KVM emulates x2APIC MSR * accesses, while interrupt injection to a running vCPU can be @@ -124,6 +125,9 @@ static void avic_deactivate_vmcb(struct vcpu_svm *svm) vmcb->control.int_ctl &= ~(AVIC_ENABLE_MASK | X2APIC_MODE_MASK); vmcb->control.avic_physical_id &= ~AVIC_PHYSICAL_MAX_INDEX_MASK; + if (!sev_es_guest(svm->vcpu.kvm)) + svm_set_intercept(svm, INTERCEPT_CR8_WRITE); + /* * If running nested and the guest uses its own MSR bitmap, there * is no need to update L0's msr bitmap diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index e365c50b6d92..ad25a6995ee6 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -1279,8 +1279,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu) svm_set_intercept(svm, INTERCEPT_CR0_WRITE); svm_set_intercept(svm, INTERCEPT_CR3_WRITE); svm_set_intercept(svm, INTERCEPT_CR4_WRITE); - if (!kvm_vcpu_apicv_active(vcpu)) - svm_set_intercept(svm, INTERCEPT_CR8_WRITE); + svm_set_intercept(svm, INTERCEPT_CR8_WRITE); set_dr_intercepts(svm); @@ -2836,9 +2835,11 @@ static int dr_interception(struct kvm_vcpu *vcpu) static int cr8_write_interception(struct kvm_vcpu *vcpu) { + u8 cr8_prev = kvm_get_cr8(vcpu); int r; - u8 cr8_prev = kvm_get_cr8(vcpu); + WARN_ON_ONCE(kvm_vcpu_apicv_active(vcpu)); + /* instruction emulation calls kvm_set_cr8() */ r = cr_interception(vcpu); if (lapic_in_kernel(vcpu)) -- 2.34.1