linux-kernel - [tip: x86/seves] x86/sev-es: Check required CPU features for SEV-ES

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Date:   Thu, 10 Sep 2020 09:22:02 -0000
From:   "tip-bot2 for Martin Radev" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Martin Radev <martin.b.radev@...il.com>,
        Joerg Roedel <jroedel@...e.de>, Borislav Petkov <bp@...e.de>,
        Kees Cook <keescook@...omium.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/seves] x86/sev-es: Check required CPU features for SEV-ES

The following commit has been merged into the x86/seves branch of tip:

Commit-ID:     1ac0dc494a9796d6f94ff392f16e0c9a8cea7021
Gitweb:        https://git.kernel.org/tip/1ac0dc494a9796d6f94ff392f16e0c9a8cea7021
Author:        Martin Radev <martin.b.radev@...il.com>
AuthorDate:    Mon, 07 Sep 2020 15:16:13 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 09 Sep 2020 18:03:48 +02:00

x86/sev-es: Check required CPU features for SEV-ES

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

To also check this in the pre-decompression stage, make has_cpuflag()
not depend on CONFIG_RANDOMIZE_BASE anymore.

Signed-off-by: Martin Radev <martin.b.radev@...il.com>
Signed-off-by: Joerg Roedel <jroedel@...e.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Kees Cook <keescook@...omium.org>
Link: https://lkml.kernel.org/r/20200907131613.12703-73-joro@8bytes.org
---
 arch/x86/boot/compressed/cpuflags.c |  4 ----
 arch/x86/boot/compressed/misc.h     |  5 +++--
 arch/x86/boot/compressed/sev-es.c   |  3 +++
 arch/x86/kernel/sev-es-shared.c     | 15 +++++++++++++++
 arch/x86/kernel/sev-es.c            |  3 +++
 5 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/arch/x86/boot/compressed/cpuflags.c b/arch/x86/boot/compressed/cpuflags.c
index 6448a81..0cc1323 100644
--- a/arch/x86/boot/compressed/cpuflags.c
+++ b/arch/x86/boot/compressed/cpuflags.c
@@ -1,6 +1,4 @@
 // SPDX-License-Identifier: GPL-2.0
-#ifdef CONFIG_RANDOMIZE_BASE
-
 #include "../cpuflags.c"
 
 bool has_cpuflag(int flag)
@@ -9,5 +7,3 @@ bool has_cpuflag(int flag)
 
 	return test_bit(flag, cpu.flags);
 }
-
-#endif
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index c0e0ffe..6d31f1b 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -85,8 +85,6 @@ void choose_random_location(unsigned long input,
 			    unsigned long *output,
 			    unsigned long output_size,
 			    unsigned long *virt_addr);
-/* cpuflags.c */
-bool has_cpuflag(int flag);
 #else
 static inline void choose_random_location(unsigned long input,
 					  unsigned long input_size,
@@ -97,6 +95,9 @@ static inline void choose_random_location(unsigned long input,
 }
 #endif
 
+/* cpuflags.c */
+bool has_cpuflag(int flag);
+
 #ifdef CONFIG_X86_64
 extern int set_page_decrypted(unsigned long address);
 extern int set_page_encrypted(unsigned long address);
diff --git a/arch/x86/boot/compressed/sev-es.c b/arch/x86/boot/compressed/sev-es.c
index 2a6c7c3..954cb27 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 4be8af2..5f83cca 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 8cac9f8..6fcfdd3 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -665,6 +665,9 @@ 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");
+
 	/* Enable SEV-ES special handling */
 	static_branch_enable(&sev_es_enable_key);