[PATCH 3.16.y-ckt 057/144] pagemap: do not leak physical addresses to non-privileged userspace

[Luis Henriques]

3.16.7-ckt10 -stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit ab676b7d6fbf4b294bf198fb27ade5b0e865c7ce upstream.

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 disallows anybody without CAP_SYS_ADMIN to read the pagemap.

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

[ Eventually we might want to do anything more finegrained, but for now
  this is the simple model.   - Linus ]

Signed-off-by: Kirill A. Shutemov <kirill.shutemov at linux.intel.com>
Acked-by: Konstantin Khlebnikov <khlebnikov at openvz.org>
Acked-by: Andy Lutomirski <luto at amacapital.net>
Cc: Pavel Emelyanov <xemul at parallels.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Mark Seaborn <mseaborn at chromium.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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 a6b314919d9d..5825f6d944ce 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1260,6 +1260,9 @@ 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");