linux-kernel - [PATCH V2 09/10] x86: Restrict MSR access when module loading is restricted

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Message-Id: <1376933171-9854-10-git-send-email-matthew.garrett@nebula.com>
Date:	Mon, 19 Aug 2013 13:26:10 -0400
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-efi@...r.kernel.org, jwboyer@...hat.com,
	keescook@...omium.org, Matthew Garrett <matthew.garrett@...ula.com>
Subject: [PATCH V2 09/10] x86: Restrict MSR access when module loading is restricted

Writing to MSRs should not be allowed if module loading is restricted,
since it could lead to execution of arbitrary code in kernel mode. Based
on a patch by Kees Cook.

Cc: Kees Cook <keescook@...omium.org>
Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
---
 arch/x86/kernel/msr.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 88458fa..d08f7e3 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -103,6 +103,9 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
 	int err = 0;
 	ssize_t bytes = 0;
 
+	if (secure_modules())
+		return -EPERM;
+
 	if (count % 8)
 		return -EINVAL;	/* Invalid chunk size */
 
@@ -150,6 +153,10 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
 			err = -EBADF;
 			break;
 		}
+		if (secure_modules()) {
+			err = -EPERM;
+			break;
+		}
 		if (copy_from_user(&regs, uregs, sizeof regs)) {
 			err = -EFAULT;
 			break;
-- 
1.8.3.1

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