RE: [PATCH v1 10/23] KVM: VMX: Add support for FRED context save/restore

Li, Xin3
2023-11-14T04:48:39Z

> > #ifdef CONFIG_X86_64
> > MSR_CSTAR, MSR_KERNEL_GS_BASE, MSR_SYSCALL_MASK, MSR_LSTAR,
> >+ MSR_IA32_FRED_RSP0, MSR_IA32_FRED_RSP1, MSR_IA32_FRED_RSP2,
> >+ MSR_IA32_FRED_RSP3, MSR_IA32_FRED_STKLVLS, MSR_IA32_FRED_SSP1,
> >+ MSR_IA32_FRED_SSP2, MSR_IA32_FRED_SSP3, MSR_IA32_FRED_CONFIG,
>
> Need to handle the case where FRED MSRs are valid but KVM cannot virtualize
> FRED, see kvm_probe_msr_to_save().

Will take care of it, thanks for reminding.

> > #endif
> > MSR_IA32_TSC, MSR_IA32_CR_PAT, MSR_VM_HSAVE_PA,
> > MSR_IA32_FEAT_CTL, MSR_IA32_BNDCFGS, MSR_TSC_AUX, @@ -1890,6
> +1893,16
> >@@ static int __kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data,
> >
> > data = (u32)data;
> > break;
> >+ case MSR_IA32_FRED_RSP0 ... MSR_IA32_FRED_CONFIG:
> >+ if (host_initiated || guest_cpuid_has(vcpu, X86_FEATURE_FRED))
> >+ break;
>
> Nothing guarantees FRED MSRs/VMCS fields exist on the hardware here. Probably
> use guest_cpu_cap_has()*.

Ah, my bad!

> *: https://lore.kernel.org/kvm/20231110235528.1561679-1-seanjc@google.com
> >+
> >+ /*
> >+ * Inject #GP upon FRED MSRs accesses from a non-FRED guest to
> >+ * make sure no malicious guest can write to FRED MSRs thus to
> >+ * corrupt host FRED MSRs.
> >+ */
>
> I think injecting #GP here is simply because KVM should emulate hardware
> behavior. To me, preventing guest from corrupting FRED MSRs is at most a
> byproduct. I prefer to drop the comment.

From security POV, this is important to mention.