pagemap: do not leak physical addresses to non-privileged userspace

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@linux.intel.com>
Acked-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Seaborn <mseaborn@chromium.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c4b2646b6d7c66f7b1c37d6fbaf033cc5ccaa561..c2546717fc2bc44eedb4af902944ebcad70c6646 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1227,6 +1227,9 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
 
 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");