Re: [Xen-devel] [PATCH 2/2] x86: explicitly disallow guest access to PPIN

[Eslam Elnikety <elnikety@xxxxxxxxxx>]

Thanks for this series, Jan.

On 30.10.19 11:39, Jan Beulich wrote:
> To fulfill the "protected" in its name, don't let the real hardware
> values "shine through". Report a control register value expressing this.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> TBD: Do we want to permit Dom0 access?
It would be nice to give an administrator a way to get PPIN outside the 
context of an MCE when needed.
> --- a/xen/arch/x86/msr.c
> +++ b/xen/arch/x86/msr.c
> @@ -135,6 +135,8 @@ int guest_rdmsr(struct vcpu *v, uint32_t
>       case MSR_TSX_FORCE_ABORT:
>       case MSR_AMD64_LWP_CFG:
>       case MSR_AMD64_LWP_CBADDR:
> +    case MSR_PPIN:
> +    case MSR_AMD_PPIN:
>           /* Not offered to guests. */
>           goto gp_fault;
>   
> @@ -237,6 +239,18 @@ int guest_rdmsr(struct vcpu *v, uint32_t
>                                      ARRAY_SIZE(msrs->dr_mask))];
>           break;
>   
> +    case MSR_PPIN_CTL:
> +        if ( d->arch.cpuid->x86_vendor != X86_VENDOR_INTEL )
> +            goto gp_fault;
> +        *val = PPIN_LOCKOUT;
> +        break;
> +
> +    case MSR_AMD_PPIN_CTL:
> +        if ( !cp->extd.amd_ppin )
> +            goto gp_fault;
> +        *val = PPIN_LOCKOUT;
> +        break;
> +
nit: It is not clear to me why you use "d->arch.cpuid->.." (and not 
"cp->..") in the first if condition.
-- Eslam

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