linux-kernel - [PATCH v8 12/16] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

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Date: Thu, 15 Feb 2024 17:01:24 +0530
From: Nikunj A Dadhania <nikunj@....com>
To: <linux-kernel@...r.kernel.org>, <thomas.lendacky@....com>, <bp@...en8.de>,
	<x86@...nel.org>, <kvm@...r.kernel.org>
CC: <mingo@...hat.com>, <tglx@...utronix.de>, <dave.hansen@...ux.intel.com>,
	<pgonda@...gle.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<nikunj@....com>
Subject: [PATCH v8 12/16] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

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>
Tested-by: Peter Gonda <pgonda@...gle.com>
---
 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 ae79f9505298..26379c70878b 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -1000,6 +1000,16 @@ 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 cpu_feature_enabled() 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