Re: [PATCH v14 05/13] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

[Borislav Petkov]

On Mon, Oct 28, 2024 at 11:04:23AM +0530, 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,
> guest execution should be terminated as the guest cannot rely on the TSC
> value provided by the hypervisor.

This should be in the comment below.

> Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
> Tested-by: Peter Gonda <pgonda@xxxxxxxxxx>
> Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  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;
> -- 
> 2.34.1
> 

-- 
Regards/Gruss,
    Boris.

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