Re: [PATCH v13 05/13] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

Xiaoyao Li
2024-10-24T07:56:41Z

On 10/21/2024 1:51 PM, Nikunj A Dadhania wrote:
> The hypervisor should not be intercepting RDTSC/RDTSCP when Secure TSC is
> enabled. A #VC exception will be generated if the RDTSC/RDTSCP instructions
> are being intercepted. If this should occur and Secure TSC is enabled,
> terminate guest execution.

There is another option to ignore the interception and just return back
to guest execution. I think it better to add some justification on why
make it fatal and terminate the guest is better than ignoring the
interception.

> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
> Tested-by: Peter Gonda <pgonda@google.com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> arch/x86/coco/sev/shared.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/arch/x86/coco/sev/shared.c b/arch/x86/coco/sev/shared.c
> index 71de53194089..c2a9e2ada659 100644
> --- a/arch/x86/coco/sev/shared.c
> +++ b/arch/x86/coco/sev/shared.c
> @@ -1140,6 +1140,16 @@ static enum es_result vc_handle_rdtsc(struct ghcb *ghcb,
> bool rdtscp = (exit_code == SVM_EXIT_RDTSCP);
> enum es_result ret;
>
> + /*
> + * RDTSC and RDTSCP should not be intercepted when Secure TSC is
> + * enabled. Terminate the SNP guest when the interception is enabled.
> + * This file is included from kernel/sev.c and boot/compressed/sev.c,
> + * use sev_status here as cc_platform_has() is not available when
> + * compiling boot/compressed/sev.c.
> + */
> + if (sev_status & MSR_AMD64_SNP_SECURE_TSC)
> + return ES_VMM_ERROR;
> +
> ret = sev_es_ghcb_hv_call(ghcb, ctxt, exit_code, 0, 0);
> if (ret != ES_OK)
> return ret;