Re: [PATCH v5 13/19] KVM:VMX: Set up interception for CET MSRs

Yang, Weijiang
2023-08-06T09:25:31Z

On 8/4/2023 4:16 PM, Chao Gao wrote:
> On Thu, Aug 03, 2023 at 12:27:26AM -0400, Yang Weijiang wrote:
>> Pass through CET MSRs when the associated feature is enabled.
>> Shadow Stack feature requires all the CET MSRs to make it
>> architectural support in guest. IBT feature only depends on
>> MSR_IA32_U_CET and MSR_IA32_S_CET to enable both user and
>> supervisor IBT. Note, This MSR design introduced an architectual
>> limitation of SHSTK and IBT control for guest, i.e., when SHSTK
>> is exposed, IBT is also available to guest from architectual level
>> since IBT relies on subset of SHSTK relevant MSRs.
>>
>> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
>
> one nit below
Thanks!
> [...]
>> +
>> + if (kvm_cpu_cap_has(X86_FEATURE_IBT)) {
>> + incpt = !guest_can_use(vcpu, X86_FEATURE_IBT);
> can you use guest_can_use() or guest_cpuid_has() consistently?
Hmm, the inspiration actually came from Sean:
Re: [RFC PATCH v2 3/6] KVM: x86: SVM: Pass through shadow stack MSRs - Sean Christopherson (kernel.org) <https://lore.kernel.org/all/ZMk14YiPw9l7ZTXP@google.com/>
it would make the code more reasonable on non-CET platforms.
>> +
>> + vmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET,
>> + MSR_TYPE_RW, incpt);
>> + vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET,
>> + MSR_TYPE_RW, incpt);
>> + }
>> +}
>> +
>> static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>> {
>> struct vcpu_vmx *vmx = to_vmx(vcpu);
>> @@ -7814,6 +7853,8 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>>
>> /* Refresh #PF interception to account for MAXPHYADDR changes. */
>> vmx_update_exception_bitmap(vcpu);
>> +
>> + vmx_update_intercept_for_cet_msr(vcpu);
>> }
>>
>> static u64 vmx_get_perf_capabilities(void)
>> --
>> 2.27.0
>>