[tip: x86/mtrr] x86/mtrr: Restrict MTRR ranges dumping and ioctl()

[tip-bot2 for Zhang Xiaoxu]

The following commit has been merged into the x86/mtrr branch of tip:

Commit-ID:     d5a8b06841082ead88493eb918dd646a12c19d8e
Gitweb:        https://git.kernel.org/tip/d5a8b06841082ead88493eb918dd646a12c19d8e
Author:        Zhang Xiaoxu <zhangxiaoxu5@xxxxxxxxxx>
AuthorDate:    Tue, 05 Nov 2019 15:17:14 +08:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Fri, 08 Nov 2019 20:59:40 +01:00

x86/mtrr: Restrict MTRR ranges dumping and ioctl()

/proc/mtrr dumps the physical memory ranges of the variable range MTRRs
along with their respective sizes and caching attributes. Since that
file is world-readable, it presents a small information leak about the
physical address ranges of a system which should be blocked.

Make that file root-only.

Make the ioctl root-only as well because the $NAME read ioctl also
allows access. Replace the checks in the write ioctls with a single one
on entry.

 [ bp: rewrite commit message. ]

Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Colin Ian King <colin.king@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Cc: zhangxiaoxu@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20191105071714.27376-1-zhangxiaoxu5@xxxxxxxxxx
---
 arch/x86/kernel/cpu/mtrr/if.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/cpu/mtrr/if.c b/arch/x86/kernel/cpu/mtrr/if.c
index 4d36dcc..8e0cee8 100644
--- a/arch/x86/kernel/cpu/mtrr/if.c
+++ b/arch/x86/kernel/cpu/mtrr/if.c
@@ -84,6 +84,15 @@ mtrr_file_del(unsigned long base, unsigned long size,
 	return reg;
 }
 
+static ssize_t
+mtrr_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
+{
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	return seq_read(file, buf, size, ppos);
+}
+
 /*
  * seq_file can seek but we ignore it.
  *
@@ -165,6 +174,9 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
 	struct mtrr_gentry gentry;
 	void __user *arg = (void __user *) __arg;
 
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
 	memset(&gentry, 0, sizeof(gentry));
 
 	switch (cmd) {
@@ -226,8 +238,6 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
 #ifdef CONFIG_COMPAT
 	case MTRRIOC32_ADD_ENTRY:
 #endif
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		err =
 		    mtrr_file_add(sentry.base, sentry.size, sentry.type, true,
 				  file, 0);
@@ -236,24 +246,18 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
 #ifdef CONFIG_COMPAT
 	case MTRRIOC32_SET_ENTRY:
 #endif
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		err = mtrr_add(sentry.base, sentry.size, sentry.type, false);
 		break;
 	case MTRRIOC_DEL_ENTRY:
 #ifdef CONFIG_COMPAT
 	case MTRRIOC32_DEL_ENTRY:
 #endif
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		err = mtrr_file_del(sentry.base, sentry.size, file, 0);
 		break;
 	case MTRRIOC_KILL_ENTRY:
 #ifdef CONFIG_COMPAT
 	case MTRRIOC32_KILL_ENTRY:
 #endif
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		err = mtrr_del(-1, sentry.base, sentry.size);
 		break;
 	case MTRRIOC_GET_ENTRY:
@@ -279,8 +283,6 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
 #ifdef CONFIG_COMPAT
 	case MTRRIOC32_ADD_PAGE_ENTRY:
 #endif
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		err =
 		    mtrr_file_add(sentry.base, sentry.size, sentry.type, true,
 				  file, 1);
@@ -289,8 +291,6 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
 #ifdef CONFIG_COMPAT
 	case MTRRIOC32_SET_PAGE_ENTRY:
 #endif
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		err =
 		    mtrr_add_page(sentry.base, sentry.size, sentry.type, false);
 		break;
@@ -298,16 +298,12 @@ mtrr_ioctl(struct file *file, unsigned int cmd, unsigned long __arg)
 #ifdef CONFIG_COMPAT
 	case MTRRIOC32_DEL_PAGE_ENTRY:
 #endif
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		err = mtrr_file_del(sentry.base, sentry.size, file, 1);
 		break;
 	case MTRRIOC_KILL_PAGE_ENTRY:
 #ifdef CONFIG_COMPAT
 	case MTRRIOC32_KILL_PAGE_ENTRY:
 #endif
-		if (!capable(CAP_SYS_ADMIN))
-			return -EPERM;
 		err = mtrr_del_page(-1, sentry.base, sentry.size);
 		break;
 	case MTRRIOC_GET_PAGE_ENTRY:
@@ -387,7 +383,7 @@ static int mtrr_open(struct inode *inode, struct file *file)
 static const struct file_operations mtrr_fops = {
 	.owner			= THIS_MODULE,
 	.open			= mtrr_open,
-	.read			= seq_read,
+	.read			= mtrr_read,
 	.llseek			= seq_lseek,
 	.write			= mtrr_write,
 	.unlocked_ioctl		= mtrr_ioctl,
@@ -436,7 +432,7 @@ static int __init mtrr_if_init(void)
 	    (!cpu_has(c, X86_FEATURE_CENTAUR_MCR)))
 		return -ENODEV;
 
-	proc_create("mtrr", S_IWUSR | S_IRUGO, NULL, &mtrr_fops);
+	proc_create("mtrr", 0600, NULL, &mtrr_fops);
 	return 0;
 }
 arch_initcall(mtrr_if_init);