[PATCH v9 20/24] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

From: Nikunj A Dadhania
Date: Fri May 31 2024 - 00:38:23 EST


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@xxxxxxx>
Tested-by: Peter Gonda <pgonda@xxxxxxxxxx>
---
arch/x86/kernel/sev-shared.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index b4f8fa0f722c..58888a086dcd 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -998,6 +998,16 @@ 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