From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-arch@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
Kees Cook <keescook@chromium.org>,
kernel-hardening@lists.openwall.com, X86 ML <x86@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Alan Cox <alan@linux.intel.com>
Subject: [kernel-hardening] Re: [PATCH v2 07/19] x86: introduce __uaccess_begin_nospec and ASM_IFENCE
Date: Fri, 12 Jan 2018 12:01:04 -0800 [thread overview]
Message-ID: <CA+55aFwhU110nyGerakLf-LHgfZDmJ6snTyQJqAHRbnxQoqbHg@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4jm7S+8ezntAo2LeOGshPdpt616RNOambOL6espzBYUvg@mail.gmail.com>
On Fri, Jan 12, 2018 at 11:26 AM, Dan Williams <dan.j.williams@intel.com> wrote:
>
> By the time we get to de-reference uptr we know it is not pointing at
> kernel memory, because access_ok would have failed and the cpu would
> have waited for that failure result before doing anything else.
I'm not actually convinced that's right in the original patches,
exactly because of the issue that Josh pointed out: even if there is a
comparison inside access_ok() that will be properly serialized, then
that comparison can (and sometimes does) just cause a truth value to
be generated, and then there might be *another* comparison of that
return value after the lfence. And while the return value is table,
the conditional branch on that comparison isn't.
The new model of just doing it together with the STAC should be fine, though.
I do think that it would be a good idea to very expressly document the
fact that it's not that the user access itself is unsafe. I do agree
that things like "get_user()" want to be protected, but not because of
any direct bugs or problems with get_user() and friends, but simply
because get_user() is an excellent source of a pointer that is
obviously controlled from a potentially attacking user space. So it's
a prime candidate for then finding _subsequent_ accesses that can then
be used to perturb the cache.
Linus
next prev parent reply other threads:[~2018-01-12 20:01 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-12 0:46 [kernel-hardening] [PATCH v2 00/19] prevent bounds-check bypass via speculative execution Dan Williams
2018-01-12 0:46 ` [kernel-hardening] [PATCH v2 01/19] Documentation: document array_ptr Dan Williams
2018-01-12 10:38 ` [kernel-hardening] " Geert Uytterhoeven
2018-01-16 21:01 ` Kees Cook
2018-01-12 0:46 ` [kernel-hardening] [PATCH v2 02/19] arm64: implement ifence_array_ptr() Dan Williams
2018-01-12 0:46 ` [kernel-hardening] [PATCH v2 03/19] arm: " Dan Williams
2018-01-12 0:46 ` [kernel-hardening] [PATCH v2 04/19] x86: implement ifence() Dan Williams
2018-01-12 2:27 ` [kernel-hardening] " Eric W. Biederman
2018-01-12 3:39 ` Dan Williams
2018-01-12 0:46 ` [kernel-hardening] [PATCH v2 05/19] x86: implement ifence_array_ptr() and array_ptr_mask() Dan Williams
2018-01-12 0:46 ` [kernel-hardening] [PATCH v2 06/19] asm-generic/barrier: mask speculative execution flows Dan Williams
2018-01-12 2:42 ` [kernel-hardening] " Eric W. Biederman
2018-01-12 9:12 ` Peter Zijlstra
2018-01-13 0:41 ` Dan Williams
2018-01-15 8:46 ` Peter Zijlstra
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 07/19] x86: introduce __uaccess_begin_nospec and ASM_IFENCE Dan Williams
2018-01-12 17:51 ` [kernel-hardening] " Josh Poimboeuf
2018-01-12 18:21 ` Dan Williams
2018-01-12 18:58 ` Josh Poimboeuf
2018-01-12 19:26 ` Dan Williams
2018-01-12 20:01 ` Linus Torvalds [this message]
2018-01-12 20:41 ` Josh Poimboeuf
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 08/19] x86: use __uaccess_begin_nospec and ASM_IFENCE in get_user paths Dan Williams
2018-01-12 1:11 ` [kernel-hardening] " Linus Torvalds
2018-01-12 1:14 ` Dan Williams
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 09/19] ipv6: prevent bounds-check bypass via speculative execution Dan Williams
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 10/19] ipv4: " Dan Williams
2018-01-12 7:59 ` [kernel-hardening] " Greg KH
2018-01-12 18:47 ` Dan Williams
2018-01-13 8:56 ` Greg KH
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 11/19] vfs, fdtable: " Dan Williams
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 12/19] userns: " Dan Williams
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 13/19] udf: " Dan Williams
2018-01-15 10:32 ` [kernel-hardening] " Jan Kara
2018-01-15 17:49 ` Dan Williams
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 14/19] [media] uvcvideo: " Dan Williams
2018-08-06 21:40 ` Laurent Pinchart
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 15/19] carl9170: " Dan Williams
2018-01-12 14:42 ` [kernel-hardening] " Christian Lamparter
2018-01-12 18:39 ` Dan Williams
2018-01-12 20:01 ` Christian Lamparter
2018-01-12 23:05 ` Dan Williams
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 16/19] p54: " Dan Williams
2018-01-12 0:47 ` [kernel-hardening] [PATCH v2 17/19] qla2xxx: " Dan Williams
2018-01-12 1:19 ` [kernel-hardening] " James Bottomley
2018-01-12 5:38 ` Dan Williams
2018-01-12 6:05 ` James Bottomley
2018-01-12 0:48 ` [kernel-hardening] [PATCH v2 18/19] cw1200: " Dan Williams
2018-01-12 0:48 ` [kernel-hardening] [PATCH v2 19/19] net: mpls: " Dan Williams
2018-01-12 1:19 ` [kernel-hardening] Re: [PATCH v2 00/19] " Linus Torvalds
2018-01-12 1:41 ` Dan Williams
2018-01-18 13:18 ` Will Deacon
2018-01-18 16:58 ` Dan Williams
2018-01-18 17:05 ` Will Deacon
2018-01-18 21:41 ` Laurent Pinchart
2018-01-13 0:15 ` Tony Luck
2018-01-13 18:51 ` Linus Torvalds
2018-01-16 19:21 ` Tony Luck
2018-01-12 10:02 ` Russell King - ARM Linux
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=CA+55aFwhU110nyGerakLf-LHgfZDmJ6snTyQJqAHRbnxQoqbHg@mail.gmail.com \
--to=torvalds@linux-foundation.org \
--cc=ak@linux.intel.com \
--cc=akpm@linux-foundation.org \
--cc=alan@linux.intel.com \
--cc=dan.j.williams@intel.com \
--cc=hpa@zytor.com \
--cc=jpoimboe@redhat.com \
--cc=keescook@chromium.org \
--cc=kernel-hardening@lists.openwall.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=tglx@linutronix.de \
--cc=viro@zeniv.linux.org.uk \
--cc=x86@kernel.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).