linux-kernel - [PATCH 11/12] x86: Require CAP_COMPROMISE

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Message-Id: <1363642353-30749-11-git-send-email-matthew.garrett@nebula.com>
Date:	Mon, 18 Mar 2013 17:32:32 -0400
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
	kexec@...ts.infradead.org, linux-pci@...r.kernel.org,
	Kees Cook <keescook@...omium.org>,
	Matthew Garrett <matthew.garrett@...ula.com>
Subject: [PATCH 11/12] x86: Require CAP_COMPROMISE_KERNEL for MSR writing

From: Kees Cook <keescook@...omium.org>

Writing to MSRs should not be allowed unless CAP_COMPROMISE_KERNEL is
set since it could lead to execution of arbitrary code in kernel mode.

Signed-off-by: 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 ce13049..fa4dc6c 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 (!capable(CAP_COMPROMISE_KERNEL))
+		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 (!capable(CAP_COMPROMISE_KERNEL)) {
+			err = -EPERM;
+			break;
+		}
 		if (copy_from_user(&regs, uregs, sizeof regs)) {
 			err = -EFAULT;
 			break;
-- 
1.8.1.2

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