Commit 6441fa61 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

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 <jmattson@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 4425f567

arch/x86/kvm/svm.c

+3 −6
Original line number Diff line number Diff line
@@ -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:

arch/x86/kvm/vmx/vmx.c

+3 −4
Original line number Diff line number Diff line
@@ -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;

arch/x86/kvm/x86.c

+22 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/kvm/x86.h

+1 −0
Original line number Diff line number Diff line
@@ -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

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