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x86/msr: Restrict MSR access when the kernel is locked down

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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>
This commit is contained in:
Matthew Garrett 2019-08-19 17:17:49 -07:00 committed by James Morris
parent 96c4f67293
commit 95f5e95f41
3 changed files with 10 additions and 0 deletions
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8
arch/x86/kernel/msr.c
View File

@ -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 *file, const char __user *buf,
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, unsigned int ioc, unsigned long arg)
err = -EFAULT;
break;
}
err = security_locked_down(LOCKDOWN_MSR);
if (err)
break;
err = wrmsr_safe_regs_on_cpu(cpu, regs);
if (err)
break;

1
include/linux/security.h
View File

@ -109,6 +109,7 @@ enum lockdown_reason {
LOCKDOWN_HIBERNATION,
LOCKDOWN_PCI_ACCESS,
LOCKDOWN_IOPORT,
LOCKDOWN_MSR,
LOCKDOWN_INTEGRITY_MAX,
LOCKDOWN_CONFIDENTIALITY_MAX,
};

1
security/lockdown/lockdown.c
View File

@ -24,6 +24,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
[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",
};