KVM: x86: avoid incorrect writes to host MSR_IA32_SPEC_CTRL

[ Upstream commit 6441fa6178f5456d1d4b512c08798888f99db185 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index c79c1a07f44b93518e97b1eb5b9562320fc871da..72bf1d8175ac229975c1623b02a6fa6c5ea91d14 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4322,12 +4322,10 @@ 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;
 
@@ -4351,13 +4349,12 @@ 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 2a1ed3aae100e7a03a8cfd86ea7c35f30562d123..8450fce70bd964bab08597ca111037f4fdfbc997 100644 (file)
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1974,12 +1974,10 @@ 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;
 
@@ -2006,7 +2004,8 @@ 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 b7f86acb8c91174d94acf1e399c8af9e1eb50465..72990c3c6faf7ed1d85ddfbcea139e1b7a639966 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10369,6 +10369,28 @@ 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 de6b55484876a1e9b9d0eef1e3e9337ca99996ef..301286d92432070c52f0c28088e206b8272ff884 100644 (file)
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -368,5 +368,6 @@ static inline bool kvm_pat_valid(u64 data)
 
 void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu);
 void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu);
+u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu);
 
 #endif