Re: [PATCH v5 08/11] KVM: VMX: Add emulation of SGX Launch Control LE hash MSRs

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/04/21 06:21, Kai Huang wrote:
> Note, KVM allows writes to the LE hash MSRs if IA32_FEATURE_CONTROL is
> unlocked.  This is technically not architectural behavior, but it's
> roughly equivalent to the arch behavior of the MSRs being writable prior
> to activating SGX[1].  Emulating SGX activation is feasible, but adds no
> tangible benefits and would just create extra work for KVM and guest
> firmware.
> 
> [1] SGX related bits in IA32_FEATURE_CONTROL cannot be set until SGX
>      is activated, e.g. by firmware.  SGX activation is triggered by
>      setting bit 0 in MSR 0x7a.  Until SGX is activated, the LE hash
>      MSRs are writable, e.g. to allow firmware to lock down the LE
>      root key with a non-Intel value.

I turned these into a comment in vmx_set_msr:

                 /*
                  * On real hardware, the LE hash MSRs are writable before
                  * the firmware sets bit 0 in MSR 0x7a ("activating" SGX),
                  * at which point SGX related bits in IA32_FEATURE_CONTROL
                  * become writable.
                  *
                  * KVM does not emulate SGX activation for simplicity, so
                  * allow writes to the LE hash MSRs if IA32_FEATURE_CONTROL
                  * is unlocked.  This is technically not architectural
                  * behavior, but close enough.
                  */

Paolo