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

[Andy Lutomirski]

On Mon, Mar 9, 2015 at 5:11 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Mon, Mar 9, 2015 at 2:11 PM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
>> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
>>
>> 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).

per-pidns like this is no good.  You shouldn't be able to create a
non-paranoid pidns if your parent is paranoid.

Also, at some point we need actual per-ns controls.  This mount option
stuff is hideous.

--Andy

>
> -Kees
>
>>
>> [1] http://googleprojectzero.blogspot.com/2015/03/exploiting-dram-rowhammer-bug-to-gain.html
>>
>> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
>> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
>> Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Mark Seaborn <mseaborn@xxxxxxxxxxxx>
>> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> ---
>>  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



-- 
Andy Lutomirski
AMA Capital Management, LLC
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