From ccd85d90ce092bdb047a7f6580f3955393833b22 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 2 Feb 2021 13:20:17 -0800 Subject: [PATCH] KVM: SVM: Treat SVM as unsupported when running as an SEV guest Don't let KVM load when running as an SEV guest, regardless of what CPUID says. Memory is encrypted with a key that is not accessible to the host (L0), thus it's impossible for L0 to emulate SVM, e.g. it'll see garbage when reading the VMCB. Technically, KVM could decrypt all memory that needs to be accessible to the L0 and use shadow paging so that L0 does not need to shadow NPT, but exposing such information to L0 largely defeats the purpose of running as an SEV guest. This can always be revisited if someone comes up with a use case for running VMs inside SEV guests. Note, VMLOAD, VMRUN, etc... will also #GP on GPAs with C-bit set, i.e. KVM is doomed even if the SEV guest is debuggable and the hypervisor is willing to decrypt the VMCB. This may or may not be fixed on CPUs that have the SVME_ADDR_CHK fix. Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson Message-Id: <20210202212017.2486595-1-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/svm.c | 5 +++++ arch/x86/mm/mem_encrypt.c | 1 + 2 files changed, 6 insertions(+) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index f923e14..3442d44 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -454,6 +454,11 @@ static int has_svm(void) return 0; } + if (sev_active()) { + pr_info("KVM is unsupported when running as an SEV guest\n"); + return 0; + } + return 1; } diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c index c79e573..c3d5f02 100644 --- a/arch/x86/mm/mem_encrypt.c +++ b/arch/x86/mm/mem_encrypt.c @@ -382,6 +382,7 @@ bool sev_active(void) { return sev_status & MSR_AMD64_SEV_ENABLED; } +EXPORT_SYMBOL_GPL(sev_active); /* Needs to be called from non-instrumentable code */ bool noinstr sev_es_active(void) -- 2.7.4