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KVM: x86: avoid incorrect writes to host MSR_IA32_SPEC_CTRL

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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>
This commit is contained in:
Paolo Bonzini
2020-01-20 16:33:06 +01:00
parent 4425f567b0
commit 6441fa6178
4 changed files with 29 additions and 10 deletions
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22
arch/x86/kvm/x86.c
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@@ -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);