[v14] Add Secure TSC support for SNP guests

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

Posted by Nikunj A Dadhania 4 weeks ago

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.

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;
-- 
2.34.1

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

Posted by Borislav Petkov 1 week, 6 days ago

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@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;
> -- 
> 2.34.1
> 

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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

Posted by Nikunj A. Dadhania 1 week, 6 days ago


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@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;
>> -- 
>> 2.34.1
>>
>

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

Posted by Borislav Petkov 1 week, 6 days ago

On Mon, Nov 11, 2024 at 10:09:14PM +0530, Nikunj A. Dadhania wrote:
> Same message in commit and the code comment ?

Yes, the explanation in the commit message is more detailed than in the
comment below. And if you have to put it in a comment, then it is preferrable
the comment contains the more detailed variant because the comment is a lot
easier to find than some commit message in git history...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette