On Thu, Dec 21, 2023 at 09:02:35AM -0500, Yang Weijiang wrote:
> Enable/disable CET MSRs interception per associated feature configuration.
> Shadow Stack feature requires all CET MSRs passed through to guest to make
> it supported in user and supervisor mode while IBT feature only depends on
> MSR_IA32_{U,S}_CETS_CET to enable user and supervisor IBT.
>
> Note, this MSR design introduced an architectural limitation of SHSTK and
> IBT control for guest, i.e., when SHSTK is exposed, IBT is also available
> to guest from architectual perspective since IBT relies on subset of SHSTK
> relevant MSRs.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
> arch/x86/kvm/vmx/vmx.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 42 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 064a5fe87948..08058b182893 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -692,6 +692,10 @@ static bool is_valid_passthrough_msr(u32 msr)
> case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 8:
> /* LBR MSRs. These are handled in vmx_update_intercept_for_lbr_msrs() */
> return true;
> + case MSR_IA32_U_CET:
> + case MSR_IA32_S_CET:
> + case MSR_IA32_PL0_SSP ... MSR_IA32_INT_SSP_TAB:
> + return true;
> }
>
> r = possible_passthrough_msr_slot(msr) != -ENOENT;
> @@ -7767,6 +7771,42 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
> vmx->pt_desc.ctl_bitmask &= ~(0xfULL << (32 + i * 4));
> }
>
> +static void vmx_update_intercept_for_cet_msr(struct kvm_vcpu *vcpu)
> +{
> + bool incpt;
> +
> + if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
> + incpt = !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);
> +
> + 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);
> + vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP,
> + MSR_TYPE_RW, incpt);
> + vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP,
> + MSR_TYPE_RW, incpt);
> + vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP,
> + MSR_TYPE_RW, incpt);
> + vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP,
> + MSR_TYPE_RW, incpt);
> + if (guest_cpuid_has(vcpu, X86_FEATURE_LM))
Looks this leading to MSR_IA32_INT_SSP_TAB not intercepted
after below steps:
Step 1. User space set cpuid w/ X86_FEATURE_LM, w/ SHSTK.
Step 2. User space set cpuid w/o X86_FEATURE_LM, w/o SHSTK.
Then MSR_IA32_INT_SSP_TAB won't be intercepted even w/o SHSTK
on guest cpuid, will this lead to inconsistency when do
rdmsr(MSR_IA32_INT_SSP_TAB) from guest in this scenario ?
> + vmx_set_intercept_for_msr(vcpu, MSR_IA32_INT_SSP_TAB,
> + MSR_TYPE_RW, incpt);
> + if (!incpt)
> + return;
> + }
> +
> + if (kvm_cpu_cap_has(X86_FEATURE_IBT)) {
> + incpt = !guest_cpuid_has(vcpu, X86_FEATURE_IBT);
> +
> + 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);
> @@ -7845,6 +7885,8 @@ 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)
> --
> 2.39.3
>
>
