linux-kernel - [PATCH v4 11/14] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

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Message-ID: <20230814055222.1056404-12-nikunj@amd.com>
Date:   Mon, 14 Aug 2023 11:22:19 +0530
From:   Nikunj A Dadhania <nikunj@....com>
To:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>
CC:     <bp@...en8.de>, <thomas.lendacky@....com>,
        <dionnaglaze@...gle.com>, <pgonda@...gle.com>, <seanjc@...gle.com>,
        <pbonzini@...hat.com>, <nikunj@....com>
Subject: [PATCH v4 11/14] 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>
---
 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 3a5b0c9c4fcc..1c22025b298f 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -912,6 +912,13 @@ 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;
-- 
2.34.1