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

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Date:	Mon, 9 Mar 2015 17:11:18 -0700
From:	Kees Cook <keescook@...omium.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Mark Seaborn <mseaborn@...omium.org>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFC, PATCH] pagemap: do not leak physical addresses to
 non-privileged userspace

On Mon, Mar 9, 2015 at 2:11 PM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.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?

I prefer Dave Hansen's approach:

http://www.spinics.net/lists/kernel/msg1941939.html

This gives finer grained control without globally dropping the ability
of a non-root process to examine pagemap details (which is the whole
point of the interface).

-Kees

>
> [1] http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Pavel Emelyanov <xemul@...allels.com>
> Cc: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Mark Seaborn <mseaborn@...omium.org>
> Cc: Andy Lutomirski <luto@...capital.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
>
> --
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-- 
Kees Cook
Chrome OS Security
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