LKML Archive on
help / color / mirror / Atom feed
From: Vlastimil Babka <>
To: Andy Lutomirski <>,
	Mark Seaborn <>
Cc: Pavel Machek <>,
	"Kirill A. Shutemov" <>,
	"" <>,
	kernel list <>,
	Andrew Morton <>,
	Linus Torvalds <>,
	"Kirill A. Shutemov" <>,
	Pavel Emelyanov <>,
	Konstantin Khlebnikov <>
Subject: Re: [RFC, PATCH] pagemap: do not leak physical addresses to non-privileged userspace
Date: Thu, 19 Mar 2015 13:51:02 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 03/17/2015 02:21 AM, Andy Lutomirski wrote:
> On Mon, Mar 16, 2015 at 5:49 PM, Mark Seaborn <> wrote:
>> On 16 March 2015 at 14:11, Pavel Machek <> wrote:
>>> Can we do anything about that? Disabling cache flushes from userland
>>> should make it no longer exploitable.
>> Unfortunately there's no way to disable userland code's use of
>> CLFLUSH, as far as I know.
>> Maybe Intel or AMD could disable CLFLUSH via a microcode update, but
>> they have not said whether that would be possible.
> The Intel people I asked last week weren't confident.  For one thing,
> I fully expect that rowhammer can be exploited using only reads and
> writes with some clever tricks involving cache associativity.  I don't
> think there are any fully-associative caches, although the cache
> replacement algorithm could make the attacks interesting.

I've been thinking the same. But maybe having to evict e.g. 16-way cache would
mean accessing 16x more lines which could reduce the frequency for a single line
below dangerous levels. Worth trying, though :)

BTW, by using clever access patterns and measurement of access latencies one
could also possibly determine which cache lines alias/colide, without needing to
read pagemap. It would just take longer. Hugepages make that simpler as well.

I just hope we are not going to disable lots of stuff including clflush and e.g.
transparent hugepages just because some part of the currently sold hardware is


> --Andy
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to  For more info on Linux MM,
> see: .
> Don't email: <a href=mailto:""> </a>

  parent reply	other threads:[~2015-03-19 12:51 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-09 21:11 [RFC, PATCH] pagemap: do not leak physical addresses to non-privileged userspace Kirill A. Shutemov
2015-03-09 21:20 ` Pavel Emelyanov
2015-03-09 22:09 ` Konstantin Khlebnikov
2015-03-10  0:11 ` Kees Cook
2015-03-10  0:19   ` Andy Lutomirski
2015-03-10  2:36     ` Dave Hansen
2015-03-16 21:11 ` Pavel Machek
2015-03-17  0:49   ` Mark Seaborn
2015-03-17  1:21     ` Andy Lutomirski
2015-03-17 11:16       ` rowhammer and pagemap (was Re: [RFC, PATCH] pagemap: do not leak physical addresses to non-privileged userspace) Pavel Machek
2015-03-17 17:58         ` One Thousand Gnomes
2015-03-23 21:26           ` Pavel Machek
2015-03-19 12:51       ` Vlastimil Babka [this message]
2015-03-23 21:26         ` [RFC, PATCH] pagemap: do not leak physical addresses to non-privileged userspace Pavel Machek
2015-03-23 22:36           ` Vlastimil Babka

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).