linux-kernel - [PATCH v16 07/13] x86/sev: Prevent GUEST_TSC_FREQ MSR interception for Secure TSC enabled guests

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Message-ID: <20250106124633.1418972-8-nikunj@amd.com>
Date: Mon, 6 Jan 2025 18:16:27 +0530
From: Nikunj A Dadhania <nikunj@....com>
To: <linux-kernel@...r.kernel.org>, <thomas.lendacky@....com>, <bp@...en8.de>,
	<x86@...nel.org>
CC: <kvm@...r.kernel.org>, <mingo@...hat.com>, <tglx@...utronix.de>,
	<dave.hansen@...ux.intel.com>, <pgonda@...gle.com>, <seanjc@...gle.com>,
	<pbonzini@...hat.com>, <nikunj@....com>, <francescolavra.fl@...il.com>
Subject: [PATCH v16 07/13] x86/sev: Prevent GUEST_TSC_FREQ MSR interception for Secure TSC enabled guests

The hypervisor should not be intercepting GUEST_TSC_FREQ MSR(0xcOO10134)
when Secure TSC is enabled. A #VC exception will be generated if the
GUEST_TSC_FREQ MSR is being intercepted. If this should occur and Secure
TSC is enabled, terminate guest execution.

Signed-off-by: Nikunj A Dadhania <nikunj@....com>
Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/include/asm/msr-index.h |  1 +
 arch/x86/coco/sev/core.c         | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 3f3e2bc99162..9a71880eec07 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -608,6 +608,7 @@
 #define MSR_AMD_PERF_CTL		0xc0010062
 #define MSR_AMD_PERF_STATUS		0xc0010063
 #define MSR_AMD_PSTATE_DEF_BASE		0xc0010064
+#define MSR_AMD64_GUEST_TSC_FREQ	0xc0010134
 #define MSR_AMD64_OSVW_ID_LENGTH	0xc0010140
 #define MSR_AMD64_OSVW_STATUS		0xc0010141
 #define MSR_AMD_PPIN_CTL		0xc00102f0
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index f49d3e97e170..dbf4531c6271 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -1431,12 +1431,19 @@ static enum es_result __vc_handle_msr_caa(struct pt_regs *regs, bool write)
 /*
  * TSC related accesses should not exit to the hypervisor when a guest is
  * executing with Secure TSC enabled, so special handling is required for
- * accesses of MSR_IA32_TSC.
+ * accesses of MSR_IA32_TSC and MSR_AMD64_GUEST_TSC_FREQ.
  */
 static enum es_result __vc_handle_secure_tsc_msrs(struct pt_regs *regs, bool write)
 {
 	u64 tsc;
 
+	/*
+	 * GUEST_TSC_FREQ should not be intercepted when Secure TSC is enabled.
+	 * Terminate the SNP guest when the interception is enabled.
+	 */
+	if (regs->cx == MSR_AMD64_GUEST_TSC_FREQ)
+		return ES_VMM_ERROR;
+
 	/*
 	 * Writes: Writing to MSR_IA32_TSC can cause subsequent reads of the TSC
 	 *         to return undefined values, so ignore all writes.
@@ -1469,6 +1476,7 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 	case MSR_SVSM_CAA:
 		return __vc_handle_msr_caa(regs, write);
 	case MSR_IA32_TSC:
+	case MSR_AMD64_GUEST_TSC_FREQ:
 		if (sev_status & MSR_AMD64_SNP_SECURE_TSC)
 			return __vc_handle_secure_tsc_msrs(regs, write);
 		else
-- 
2.34.1