From 6441fa6178f5456d1d4b512c08798888f99db185 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 20 Jan 2020 16:33:06 +0100 Subject: [PATCH] KVM: x86: avoid incorrect writes to host MSR_IA32_SPEC_CTRL If the guest is configured to have SPEC_CTRL but the host does not (which is a nonsensical configuration but these are not explicitly forbidden) then a host-initiated MSR write can write vmx->spec_ctrl (respectively svm->spec_ctrl) and trigger a #GP when KVM tries to restore the host value of the MSR. Add a more comprehensive check for valid bits of SPEC_CTRL, covering host CPUID flags and, since we are at it and it is more correct that way, guest CPUID flags too. For AMD, remove the unnecessary is_guest_mode check around setting the MSR interception bitmap, so that the code looks the same as for Intel. Cc: Jim Mattson Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm.c | 9 +++------ arch/x86/kvm/vmx/vmx.c | 7 +++---- arch/x86/kvm/x86.c | 22 ++++++++++++++++++++++ arch/x86/kvm/x86.h | 1 + 4 files changed, 29 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index b7c5369c7998..235a7e51de96 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -4324,12 +4324,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) return 1; - /* The STIBP bit doesn't fault even if it's not advertised */ - if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD)) + if (data & ~kvm_spec_ctrl_valid_bits(vcpu)) return 1; svm->spec_ctrl = data; - if (!data) break; @@ -4353,13 +4351,12 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) if (data & ~PRED_CMD_IBPB) return 1; - + if (!boot_cpu_has(X86_FEATURE_AMD_IBPB)) + return 1; if (!data) break; wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB); - if (is_guest_mode(vcpu)) - break; set_msr_interception(svm->msrpm, MSR_IA32_PRED_CMD, 0, 1); break; case MSR_AMD64_VIRT_SPEC_CTRL: diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index bdbf27e92851..112d2314231d 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -1998,12 +1998,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)) return 1; - /* The STIBP bit doesn't fault even if it's not advertised */ - if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD)) + if (data & ~kvm_spec_ctrl_valid_bits(vcpu)) return 1; vmx->spec_ctrl = data; - if (!data) break; @@ -2037,7 +2035,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) if (data & ~PRED_CMD_IBPB) return 1; - + if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL)) + return 1; if (!data) break; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9f24f5d16854..b690c0d70793 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10389,6 +10389,28 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu) } EXPORT_SYMBOL_GPL(kvm_arch_no_poll); +u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu) +{ + uint64_t bits = SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD; + + /* The STIBP bit doesn't fault even if it's not advertised */ + if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) && + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS)) + bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP); + if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL) && + !boot_cpu_has(X86_FEATURE_AMD_IBRS)) + bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP); + + if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL_SSBD) && + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) + bits &= ~SPEC_CTRL_SSBD; + if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) && + !boot_cpu_has(X86_FEATURE_AMD_SSBD)) + bits &= ~SPEC_CTRL_SSBD; + + return bits; +} +EXPORT_SYMBOL_GPL(kvm_spec_ctrl_valid_bits); EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit); EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio); diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index ab715cee3653..dd6e34d0a881 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -367,5 +367,6 @@ static inline bool kvm_pat_valid(u64 data) void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu); void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu); +u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu); #endif -- GitLab