linux-kernel - [RFC PATCH] security: Add a config option to disable security mitigations

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Message-Id: <20200618010755.4179-1-bobby.prani@gmail.com>
Date:   Wed, 17 Jun 2020 18:07:54 -0700
From:   Pranith Kumar <bobby.prani@...il.com>
To:     James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Qais Yousef <qais.yousef@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Tyler Hicks <tyhicks@...onical.com>,
        linux-kernel@...r.kernel.org (open list),
        linux-security-module@...r.kernel.org (open list:SECURITY SUBSYSTEM)
Subject: [RFC PATCH] security: Add a config option to disable security mitigations

Instead of having to pass 'mitigations=off' on the kernel command line,
add a config option that has a similar effect.

Adding this makes it easier to disable mitigations in scenarios where
you cannot modify the command line or are unable to pass a command line
while booting.

Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
---
 kernel/cpu.c     | 2 +-
 security/Kconfig | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6ff2578ecf17..584eb39585d6 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2542,7 +2542,7 @@ early_param("mitigations", mitigations_parse_cmdline);
 /* mitigations=off */
 bool cpu_mitigations_off(void)
 {
-	return cpu_mitigations == CPU_MITIGATIONS_OFF;
+	return cpu_mitigations == CPU_MITIGATIONS_OFF || IS_ENABLED(CONFIG_DISABLE_MITIGATIONS);
 }
 EXPORT_SYMBOL_GPL(cpu_mitigations_off);
 
diff --git a/security/Kconfig b/security/Kconfig
index cd3cc7da3a55..90b8e9c89a6d 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -65,6 +65,14 @@ config PAGE_TABLE_ISOLATION
 
 	  See Documentation/x86/pti.rst for more details.
 
+config DISABLE_MITIGATIONS
+	bool "Disable kernel security mitigations"
+	default n
+	help
+	  This turns off the kernel security mitigations. This is
+	  equivalent to passing 'mitigations=off' on the kernel
+	  command line.
+
 config SECURITY_INFINIBAND
 	bool "Infiniband Security Hooks"
 	depends on SECURITY && INFINIBAND
-- 
2.27.0