From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Netdev <netdev@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 06/18] x86, barrier: stop speculation for failed access_ok
Date: Sat, 6 Jan 2018 10:39:39 -0800 [thread overview]
Message-ID: <20180106183937.vkseldf4arkdlkum@ast-mbp> (raw)
In-Reply-To: <CAPcyv4jqKmnkL1CfHVccHvocmSD4PamqOy4bPsO1789D+107FQ@mail.gmail.com>
On Sat, Jan 06, 2018 at 10:29:49AM -0800, Dan Williams wrote:
> On Sat, Jan 6, 2018 at 10:13 AM, Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> > On Sat, Jan 06, 2018 at 12:32:42PM +0000, Alan Cox wrote:
> >> On Fri, 5 Jan 2018 18:52:07 -0800
> >> Linus Torvalds <torvalds@linux-foundation.org> wrote:
> >>
> >> > On Fri, Jan 5, 2018 at 5:10 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> >> > > From: Andi Kleen <ak@linux.intel.com>
> >> > >
> >> > > When access_ok fails we should always stop speculating.
> >> > > Add the required barriers to the x86 access_ok macro.
> >> >
> >> > Honestly, this seems completely bogus.
> >>
> >> Also for x86-64 if we are trusting that an AND with a constant won't get
> >> speculated into something else surely we can just and the address with ~(1
> >> << 63) before copying from/to user space ? The user will then just
> >> speculatively steal their own memory.
> >
> > +1
> >
> > Any type of straight line code can address variant 1.
> > Like changing:
> > array[index]
> > into
> > array[index & mask]
> > works even when 'mask' is a variable.
> > To proceed with speculative load from array cpu has to speculatively
> > load 'mask' from memory and speculatively do '&' alu.
> > If attacker cannot influence 'mask' the speculative value of it
> > will bound 'index & mask' value to be within array limits.
> >
> > I think "lets sprinkle lfence everywhere" approach is going to
> > cause serious performance degradation. Yet people pushing for lfence
> > didn't present any numbers.
> > Last time lfence was removed from the networking drivers via dma_rmb()
> > packet-per-second metric jumped 10-30%. lfence forces all outstanding loads
> > to complete. If any prior load is waiting on L3 or memory,
> > lfence will cause 100+ ns stall and overall kernel performance will tank.
>
> You are conflating dma_rmb() with the limited cases where
> nospec_array_ptr() is used. I need help determining what the
> performance impact of those limited places are.
really? fdtable, access_ok, net/ipv[46] is not critical path?
> > If kernel adopts this "lfence everywhere" approach it will be
> > the end of the kernel as we know it. All high performance operations
> > will move into user space. Networking and IO will be first.
> > Since it will takes years to design new cpus and even longer
> > to upgrade all servers the industry will have no choice,
> > but to move as much logic as possible from the kernel.
> >
> > kpti already made crossing user/kernel boundary slower, but
> > kernel itself is still fast. If kernel will have lfence everywhere
> > the kernel itself will be slow.
> >
> > In that sense retpolining the kernel is not as horrible as it sounds,
> > since both user space and kernel has to be retpolined.
>
> retpoline is variant-2, this patch series is about variant-1.
that's exactly the point. Don't slow down the kernel with lfences
to solve variant 1. retpoline for 2 is ok from long term kernel
viability perspective.
next prev parent reply other threads:[~2018-01-06 18:39 UTC|newest]
Thread overview: 162+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-06 1:09 [PATCH 00/18] prevent bounds-check bypass via speculative execution Dan Williams
2018-01-06 1:09 ` [PATCH 01/18] asm-generic/barrier: add generic nospec helpers Dan Williams
2018-01-06 2:55 ` Linus Torvalds
2018-01-06 5:23 ` Dan Williams
2018-01-06 17:08 ` Mark Rutland
2018-01-06 1:10 ` [PATCH 02/18] Documentation: document " Dan Williams
2018-01-08 16:29 ` Jonathan Corbet
2018-01-08 17:09 ` Mark Rutland
2018-01-08 21:19 ` Jonathan Corbet
2018-01-06 1:10 ` [PATCH 03/18] arm64: implement nospec_ptr() Dan Williams
2018-01-06 1:10 ` [PATCH 04/18] arm: " Dan Williams
2018-01-10 2:04 ` Laura Abbott
2018-01-10 7:40 ` Hanjun Guo
2018-01-10 17:24 ` Laura Abbott
2018-01-06 1:10 ` [PATCH 05/18] x86: implement nospec_barrier() Dan Williams
2018-01-06 1:10 ` [PATCH 06/18] x86, barrier: stop speculation for failed access_ok Dan Williams
2018-01-06 2:52 ` Linus Torvalds
2018-01-06 3:09 ` Linus Torvalds
2018-01-06 23:31 ` Dan Williams
2018-01-07 1:20 ` Linus Torvalds
2018-01-08 21:09 ` Dan Williams
2018-01-08 23:44 ` Linus Torvalds
2018-01-08 23:53 ` Dan Williams
2018-01-06 5:47 ` Dan Williams
2018-01-06 12:32 ` Alan Cox
2018-01-06 17:56 ` Linus Torvalds
2018-01-06 18:13 ` Alexei Starovoitov
2018-01-06 18:29 ` Dan Williams
2018-01-06 18:39 ` Alexei Starovoitov [this message]
2018-01-06 18:54 ` Dan Williams
2018-01-06 19:25 ` Alexei Starovoitov
2018-01-06 19:36 ` Dan Williams
2018-01-06 19:41 ` Thomas Gleixner
2018-01-08 10:02 ` Andrea Arcangeli
2018-01-06 18:38 ` Alan Cox
2018-01-06 18:51 ` Alexei Starovoitov
2018-01-06 19:55 ` Alan Cox
2018-01-06 20:09 ` Alexei Starovoitov
2018-01-06 20:22 ` Alan Cox
2018-01-06 21:17 ` Alexei Starovoitov
2018-01-06 21:21 ` Thomas Gleixner
2018-01-06 23:05 ` Alan Cox
2018-01-07 3:38 ` Alexei Starovoitov
2018-01-07 6:33 ` Willy Tarreau
2018-01-07 19:47 ` Linus Torvalds
2018-01-07 20:12 ` Willy Tarreau
2018-01-07 20:17 ` Linus Torvalds
2018-01-07 20:56 ` Thomas Gleixner
2018-01-08 2:23 ` David Miller
2018-01-08 7:38 ` Greg KH
2018-01-07 22:15 ` Willy Tarreau
2018-01-07 20:15 ` Dan Williams
2018-01-08 2:24 ` Alexei Starovoitov
2018-01-08 9:51 ` Peter Zijlstra
2018-01-08 18:21 ` Ingo Molnar
2018-01-08 12:00 ` David Laight
2018-01-08 12:12 ` Alan Cox
2018-01-08 12:33 ` David Laight
2018-01-07 10:08 ` Thomas Gleixner
2018-01-08 2:09 ` Alexei Starovoitov
2018-01-07 13:59 ` Alan Cox
2018-01-08 2:57 ` Alexei Starovoitov
2018-01-08 9:57 ` Peter Zijlstra
2018-01-06 20:42 ` Willy Tarreau
2018-01-07 1:36 ` David Miller
2018-01-07 17:19 ` James Bottomley
2018-01-07 18:31 ` Thomas Gleixner
2018-01-08 2:04 ` David Miller
2018-01-07 19:24 ` Alan Cox
2018-01-09 21:41 ` Josh Poimboeuf
2018-01-09 21:47 ` Dan Williams
2018-01-09 21:49 ` Josh Poimboeuf
2018-01-09 21:59 ` Dan Williams
2018-01-09 22:23 ` Josh Poimboeuf
2018-01-09 22:35 ` Dan Williams
2018-01-06 1:10 ` [PATCH 07/18] [media] uvcvideo: prevent bounds-check bypass via speculative execution Dan Williams
2018-01-06 9:09 ` Greg KH
2018-01-06 9:40 ` Greg KH
2018-01-06 17:41 ` Dan Williams
2018-01-07 9:09 ` Greg KH
2018-01-07 19:37 ` Dan Williams
2018-01-09 8:40 ` Laurent Pinchart
2018-01-09 10:04 ` Greg KH
2018-01-09 14:26 ` Laurent Pinchart
2018-01-09 14:47 ` Greg KH
2018-01-08 11:23 ` Laurent Pinchart
2018-01-09 2:11 ` Dan Williams
2018-01-06 1:10 ` [PATCH 08/18] carl9170: " Dan Williams
2018-01-06 10:01 ` Sergei Shtylyov
2018-01-06 14:23 ` Christian Lamparter
2018-01-06 15:06 ` Alan Cox
2018-01-06 16:38 ` Christian Lamparter
2018-01-06 16:34 ` Dan Williams
2018-01-06 1:10 ` [PATCH 09/18] p54: " Dan Williams
2018-01-06 10:01 ` Sergei Shtylyov
2018-01-06 1:10 ` [PATCH 10/18] qla2xxx: " Dan Williams
2018-01-06 9:03 ` Greg KH
2018-01-06 9:42 ` Greg KH
2018-01-11 22:15 ` Dan Williams
2018-01-12 7:27 ` Greg KH
2018-01-12 15:25 ` James Bottomley
2018-01-06 1:10 ` [PATCH 11/18] cw1200: " Dan Williams
2018-01-06 1:10 ` [PATCH 12/18] Thermal/int340x: " Dan Williams
2018-01-06 1:53 ` Srinivas Pandruvada
2018-01-06 1:57 ` Dan Williams
2018-01-06 17:24 ` Srinivas Pandruvada
2018-01-06 10:03 ` Sergei Shtylyov
2018-01-06 1:11 ` [PATCH 13/18] ipv6: " Dan Williams
2018-01-06 10:04 ` Sergei Shtylyov
2018-01-06 14:48 ` Stephen Hemminger
2018-01-06 18:05 ` Dan Williams
2018-01-06 1:11 ` [PATCH 14/18] ipv4: " Dan Williams
2018-01-06 9:00 ` Greg KH
2018-01-06 9:01 ` Greg KH
2018-01-06 12:23 ` Alan Cox
2018-01-06 15:14 ` Greg KH
2018-01-06 16:29 ` Dan Williams
2018-01-06 18:10 ` Dan Williams
2018-01-06 10:04 ` Sergei Shtylyov
2018-01-06 1:11 ` [PATCH 15/18] vfs, fdtable: " Dan Williams
2018-01-06 10:05 ` Sergei Shtylyov
2018-01-06 1:11 ` [PATCH 16/18] net: mpls: " Dan Williams
2018-01-06 10:06 ` Sergei Shtylyov
2018-01-09 3:11 ` Eric W. Biederman
2018-01-09 3:42 ` Dan Williams
2018-01-09 4:13 ` Linus Torvalds
2018-01-09 4:21 ` Linus Torvalds
2018-01-10 0:48 ` Dan Williams
2018-01-10 1:33 ` Dan Williams
2018-01-10 1:57 ` Alexei Starovoitov
2018-01-10 2:22 ` Dan Williams
2018-01-10 3:07 ` Alexei Starovoitov
2018-01-10 3:27 ` Linus Torvalds
2018-01-09 16:17 ` Eric W. Biederman
2018-01-09 18:01 ` Dan Williams
2018-01-10 0:54 ` Eric W. Biederman
2018-01-10 1:31 ` Dan Williams
2018-01-06 1:11 ` [PATCH 17/18] udf: " Dan Williams
2018-01-08 10:20 ` Jan Kara
2018-01-06 1:11 ` [PATCH 18/18] userns: " Dan Williams
2018-01-06 2:22 ` [PATCH 00/18] " Eric W. Biederman
2018-01-06 6:30 ` Dan Williams
2018-01-08 10:08 ` Peter Zijlstra
2018-01-08 11:14 ` Laurent Pinchart
2018-01-08 11:43 ` Alan Cox
2018-01-08 11:55 ` Peter Zijlstra
2018-01-08 18:33 ` Ingo Molnar
2018-01-08 16:20 ` Bart Van Assche
2018-01-06 18:56 ` Florian Fainelli
2018-01-06 18:59 ` Arjan van de Ven
2018-01-06 19:37 ` Dan Williams
2018-01-06 20:07 ` Dan Williams
2018-01-08 4:49 ` Bart Van Assche
2018-01-08 13:33 ` Arjan van de Ven
2018-01-09 19:34 ` Jiri Kosina
2018-01-09 19:44 ` Dan Williams
2018-01-09 20:55 ` Josh Poimboeuf
2018-01-11 9:54 ` Jiri Kosina
2018-01-11 15:58 ` Dan Williams
2018-01-11 16:34 ` Daniel Borkmann
2018-01-13 11:33 ` QingFeng Hao
2018-01-09 0:12 [PATCH 06/18] x86, barrier: stop speculation for failed access_ok Linus Torvalds
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:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180106183937.vkseldf4arkdlkum@ast-mbp \
--to=alexei.starovoitov@gmail.com \
--cc=ak@linux.intel.com \
--cc=arnd@arndb.de \
--cc=dan.j.williams@intel.com \
--cc=gnomes@lxorguk.ukuu.org.uk \
--cc=gregkh@linuxfoundation.org \
--cc=hpa@zytor.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* 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).