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

Message ID 20231030063652.68675-12-nikunj@amd.com
State New
Headers
Series Add Secure TSC support for SNP guests |

Commit Message

Nikunj A. Dadhania Oct. 30, 2023, 6:36 a.m. UTC 
  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(+)

Comments

Tom Lendacky Oct. 30, 2023, 8:32 p.m. UTC | #1 
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;
Nikunj A. Dadhania Nov. 2, 2023, 5:47 a.m. UTC | #2 
On 10/31/2023 2:02 AM, Tom Lendacky wrote:
> 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.

Right, for sev-shared.c, cc_platform_has() is not available when compiling boot/compressed.

Regards
Nikunj
diff mbox series

Patch

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