From: Matthew Garrett <mjg59@srcf.ucam.org>
Date: Mon, 19 Aug 2019 17:17:49 -0700
Subject: x86/msr: Restrict MSR access when the kernel is locked down
Patch-mainline: v5.4-rc1
Git-commit: 95f5e95f41dff31b2a4566c5a8975c08a49ae4e3
References: jsc#SLE-9870
Writing to MSRs should not be allowed if the kernel is locked down, since
it could lead to execution of arbitrary code in kernel mode. Based on a
patch by Kees Cook.
Signed-off-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
cc: x86@kernel.org
Signed-off-by: James Morris <jmorris@namei.org>
Acked-by: Lee, Chun-Yi <jlee@suse.com>
---
arch/x86/kernel/msr.c | 8 ++++++++
include/linux/security.h | 1 +
security/lockdown/lockdown.c | 1 +
3 files changed, 10 insertions(+)
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -34,6 +34,7 @@
#include <linux/notifier.h>
#include <linux/uaccess.h>
#include <linux/gfp.h>
+#include <linux/security.h>
#include <asm/cpufeature.h>
#include <asm/msr.h>
@@ -79,6 +80,10 @@ static ssize_t msr_write(struct file *fi
int err = 0;
ssize_t bytes = 0;
+ err = security_locked_down(LOCKDOWN_MSR);
+ if (err)
+ return err;
+
if (count % 8)
return -EINVAL; /* Invalid chunk size */
@@ -130,6 +135,9 @@ static long msr_ioctl(struct file *file,
err = -EFAULT;
break;
}
+ err = security_locked_down(LOCKDOWN_MSR);
+ if (err)
+ break;
err = wrmsr_safe_regs_on_cpu(cpu, regs);
if (err)
break;
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -109,6 +109,7 @@ enum lockdown_reason {
LOCKDOWN_HIBERNATION,
LOCKDOWN_PCI_ACCESS,
LOCKDOWN_IOPORT,
+ LOCKDOWN_MSR,
LOCKDOWN_INTEGRITY_MAX,
LOCKDOWN_CONFIDENTIALITY_MAX,
};
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -24,6 +24,7 @@ static char *lockdown_reasons[LOCKDOWN_C
[LOCKDOWN_HIBERNATION] = "hibernation",
[LOCKDOWN_PCI_ACCESS] = "direct PCI access",
[LOCKDOWN_IOPORT] = "raw io port access",
+ [LOCKDOWN_MSR] = "raw MSR access",
[LOCKDOWN_INTEGRITY_MAX] = "integrity",
[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
};