From: Paolo Bonzini <pbonzini@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Jim Mattson <jmattson@redhat.com>
Subject: [PATCH] KVM: x86: avoid incorrect writes to host MSR_IA32_SPEC_CTRL
Date: Tue, 21 Jan 2020 14:48:07 +0100 [thread overview]
Message-ID: <1579614487-44583-3-git-send-email-pbonzini@redhat.com> (raw)
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 <jmattson@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
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..141fb129c6bf 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);
+bool 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..bc38ac695776 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);
+bool kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu);
#endif
--
1.8.3.1
next reply other threads:[~2020-01-21 13:48 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-21 13:48 Paolo Bonzini [this message]
2020-01-24 8:00 ` [PATCH] KVM: x86: avoid incorrect writes to host MSR_IA32_SPEC_CTRL Xiaoyao Li
2020-01-24 8:22 ` Paolo Bonzini
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