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

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Date:   Mon, 30 Oct 2023 15:32:21 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, kvm@...r.kernel.org
Cc:     bp@...en8.de, mingo@...hat.com, tglx@...utronix.de,
        dave.hansen@...ux.intel.com, dionnaglaze@...gle.com,
        pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v5 11/14] x86/sev: Prevent RDTSC/RDTSCP interception for
 Secure TSC enabled guests

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@....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;