[RFC, PATCH] pagemap: do not leak physical addresses to non-privileged userspace

["Kirill A. Shutemov" <kirill@shutemov.name>]

From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>

As pointed by recent post[1] on exploiting DRAM physical imperfection,
/proc/PID/pagemap exposes sensitive information which can be used to do
attacks.

This is RFC patch which disallow anybody without CAP_SYS_ADMIN to read
the pagemap.

Any comments?

[1] http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Seaborn <mseaborn@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>
---
 fs/proc/task_mmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 246eae84b13b..b72b36e64286 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1322,6 +1322,9 @@ out:
 
 static int pagemap_open(struct inode *inode, struct file *file)
 {
+	/* do not disclose physical addresses: attack vector */
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
 	pr_warn_once("Bits 55-60 of /proc/PID/pagemap entries are about "
 			"to stop being page-shift some time soon. See the "
 			"linux/Documentation/vm/pagemap.txt for details.\n");
-- 
2.3.1