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

[Nikunj A. Dadhania]

On 11/11/2024 9:23 PM, Borislav Petkov wrote:
> 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.

Same message in commit and the code comment ?

> 
>> 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
>>
>