From 27bd5fdc24c0d5d1306f968ef24105c4577242b0 Mon Sep 17 00:00:00 2001 From: Nikunj A Dadhania Date: Fri, 31 May 2024 04:46:42 +0000 Subject: [PATCH] KVM: SEV-ES: Prevent MSR access post VMSA encryption KVM currently allows userspace to read/write MSRs even after the VMSA is encrypted. This can cause unintentional issues if MSR access has side- effects. For ex, while migrating a guest, userspace could attempt to migrate MSR_IA32_DEBUGCTLMSR and end up unintentionally disabling LBRV on the target. Fix this by preventing access to those MSRs which are context switched via the VMSA, once the VMSA is encrypted. Suggested-by: Sean Christopherson Signed-off-by: Nikunj A Dadhania Signed-off-by: Ravi Bangoria Message-ID: <20240531044644.768-2-ravi.bangoria@amd.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/svm.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index 1d3c8be39479..f265361f4518 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -2822,10 +2822,24 @@ static int svm_get_msr_feature(struct kvm_msr_entry *msr) return 0; } +static bool +sev_es_prevent_msr_access(struct kvm_vcpu *vcpu, struct msr_data *msr_info) +{ + return sev_es_guest(vcpu->kvm) && + vcpu->arch.guest_state_protected && + svm_msrpm_offset(msr_info->index) != MSR_INVALID && + !msr_write_intercepted(vcpu, msr_info->index); +} + static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) { struct vcpu_svm *svm = to_svm(vcpu); + if (sev_es_prevent_msr_access(vcpu, msr_info)) { + msr_info->data = 0; + return -EINVAL; + } + switch (msr_info->index) { case MSR_AMD64_TSC_RATIO: if (!msr_info->host_initiated && @@ -2976,6 +2990,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) u32 ecx = msr->index; u64 data = msr->data; + + if (sev_es_prevent_msr_access(vcpu, msr)) + return -EINVAL; + switch (ecx) { case MSR_AMD64_TSC_RATIO: -- 2.39.5