linux-kernel - [PATCH v4 75/75] x86/sev-es: Check required CPU features for SEV-ES

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Message-Id: <20200714120917.11253-76-joro@8bytes.org>
Date:   Tue, 14 Jul 2020 14:09:17 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        Martin Radev <martin.b.radev@...il.com>, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH v4 75/75] x86/sev-es: Check required CPU features for SEV-ES

From: Martin Radev <martin.b.radev@...il.com>

Make sure the machine supports RDRAND, otherwise there is no trusted
source of of randomness in the system.

Signed-off-by: Martin Radev <martin.b.radev@...il.com>
Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/boot/compressed/sev-es.c |  3 +++
 arch/x86/kernel/sev-es-shared.c   | 15 +++++++++++++++
 arch/x86/kernel/sev-es.c          |  3 +++
 3 files changed, 21 insertions(+)

diff --git a/arch/x86/boot/compressed/sev-es.c b/arch/x86/boot/compressed/sev-es.c
index b522c18c0588..eb1a8b5cc753 100644
--- a/arch/x86/boot/compressed/sev-es.c
+++ b/arch/x86/boot/compressed/sev-es.c
@@ -145,6 +145,9 @@ void sev_es_shutdown_ghcb(void)
 	if (!boot_ghcb)
 		return;
 
+	if (!sev_es_check_cpu_features())
+		error("SEV-ES CPU Features missing.");
+
 	/*
 	 * GHCB Page must be flushed from the cache and mapped encrypted again.
 	 * Otherwise the running kernel will see strange cache effects when
diff --git a/arch/x86/kernel/sev-es-shared.c b/arch/x86/kernel/sev-es-shared.c
index 608f76d0d088..56de70cb80d8 100644
--- a/arch/x86/kernel/sev-es-shared.c
+++ b/arch/x86/kernel/sev-es-shared.c
@@ -9,6 +9,21 @@
  * and is included directly into both code-bases.
  */
 
+#ifndef __BOOT_COMPRESSED
+#define error(v)	pr_err(v)
+#define has_cpuflag(f)	boot_cpu_has(f)
+#endif
+
+static bool __init sev_es_check_cpu_features(void)
+{
+	if (!has_cpuflag(X86_FEATURE_RDRAND)) {
+		error("RDRAND instruction not supported - no trusted source of randomness available\n");
+		return false;
+	}
+
+	return true;
+}
+
 static void sev_es_terminate(unsigned int reason)
 {
 	u64 val = GHCB_SEV_TERMINATE;
diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index 61308f9c8138..481ea00c58b6 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -682,6 +682,9 @@ void __init sev_es_init_vc_handling(void)
 	if (!sev_es_active())
 		return;
 
+	if (!sev_es_check_cpu_features())
+		panic("SEV-ES CPU Features missing");
+
 	/* Initialize per-cpu GHCB pages */
 	for_each_possible_cpu(cpu) {
 		sev_es_alloc_runtime_data(cpu);
-- 
2.27.0