linux-kernel - [PATCH v15 05/13] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

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Message-ID: <20241203090045.942078-6-nikunj@amd.com>
Date: Tue, 3 Dec 2024 14:30:37 +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 v15 05/13] 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,
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@....com>
Tested-by: Peter Gonda <pgonda@...gle.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/coco/sev/shared.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/coco/sev/shared.c b/arch/x86/coco/sev/shared.c
index 71de53194089..879ab48b705c 100644
--- a/arch/x86/coco/sev/shared.c
+++ b/arch/x86/coco/sev/shared.c
@@ -1140,6 +1140,20 @@ static enum es_result vc_handle_rdtsc(struct ghcb *ghcb,
 	bool rdtscp = (exit_code == SVM_EXIT_RDTSCP);
 	enum es_result ret;
 
+	/*
+	 * 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 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