Re: [PATCH v5 11/14] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

Tom Lendacky
2023-10-30T20:32:28Z

On 10/30/23 01:36, 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.
>
> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
> ---
> arch/x86/kernel/sev-shared.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index ccb0915e84e1..833b0ae38f0b 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -991,6 +991,13 @@ 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.
> + */
> + if (sev_status & MSR_AMD64_SNP_SECURE_TSC)

If you have to use sev_status, then please document why cc_platform_has()
can't be used in the comment above.

Thanks,
Tom

> + return ES_VMM_ERROR;
> +
> ret = sev_es_ghcb_hv_call(ghcb, ctxt, exit_code, 0, 0);
> if (ret != ES_OK)
> return ret;