From: Willy Tarreau <w@1wt.eu>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "security@kernel.org" <security@kernel.org>,
Jan Beulich <jbeulich@suse.com>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
X86 ML <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
xen-devel <xen-devel@lists.xen.org>,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
Sasha Levin <sasha.levin@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH 4/3] x86/ldt: allow to disable modify_ldt at runtime
Date: Sat, 25 Jul 2015 20:45:45 +0200 [thread overview]
Message-ID: <20150725184545.GB17740__7139.50914000652$1437850104$gmane$org@1wt.eu> (raw)
In-Reply-To: <CALCETrXeWdugPpAkKhUD=f7ftuYSM5fxaPxnF2=PwygupP2_4w@mail.gmail.com>
On Sat, Jul 25, 2015 at 10:42:14AM -0700, Andy Lutomirski wrote:
> On Sat, Jul 25, 2015 at 9:33 AM, Willy Tarreau <w@1wt.eu> wrote:
> > On Sat, Jul 25, 2015 at 09:08:39AM -0700, Andy Lutomirski wrote:
> >> There's one thing that I think is incomplete here. Currently, espfix
> >> triggers if SS points to the LDT. It's possible for SS to point to
> >> the LDT even with modify_ldt disabled, and there's a decent amount of
> >> attack surface there.
> >>
> >> Can we improve this? Two ideas:
> >>
> >> 1. In the asm, patch out or otherwise disable espfix if that sysctl
> >> has never been set. (Ick.)
> >>
> >> 2. When modify_ldt is runtime-disabled (or compile-time disabled,
> >> perhaps), disallow setting the LDT bit in SS in the handful of places
> >> that would allow it (ptrace and sigreturn off the top of my head). We
> >> don't need to worry about (regs->ss & 4) being set on kernel entry
> >> because we'll never be in user mode with that bit set if the LDT is
> >> disabled, but that bit could still be set using kernel APIs. (In
> >> fact, my sigreturn test does exactly that.)
> >>
> >> Hmm. With synchronous LDT, we could plausibly check at runtime in the
> >> espfix code, too. We used to use LAR to do this, but hpa removed it
> >> when he realized that it was racy. It shouldn't be racy any more,
> >> because, with my patches applied, the LDT never changes while
> >> interrupts are off.
> >
> > I understand it's not complete but I'm a bit bothered with conflating
> > this sysctl with other setting methods, because if the purpose of the
> > sysctl is to disable the syscall, it should do that only. I'd rather
> > document that it's less complete than the Kconfig method and continue
> > to recommend using your option whenever possible (eg: all my kernels
> > will use it just as I've already disabled X86_16BIT everywhere).
> >
>
> Agreed. We can certainly tighten up the espfix code later.
>
> > Also one benefit of having both options is that it will mechanically
> > make LDT a much less interesting target for future attacks, since it
> > will significantly reduce the likeliness of success, hence the motivation
> > for writing exploits that only work in conferences.
> >
>
> Patch looks fine to me.
OK thanks.
Willy
next prev parent reply other threads:[~2015-07-25 18:45 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1437802102.git.luto@kernel.org>
2015-07-25 5:36 ` [PATCH v4 1/3] x86/ldt: Make modify_ldt synchronous Andy Lutomirski
2015-07-25 5:36 ` [PATCH v4 2/3] x86/ldt: Make modify_ldt optional Andy Lutomirski
2015-07-25 5:36 ` [PATCH v4 3/3] selftests/x86, x86/ldt: Add a selftest for modify_ldt Andy Lutomirski
2015-07-25 6:27 ` [PATCH v4 0/3] x86: modify_ldt improvement, test, and config option Willy Tarreau
[not found] ` <12ddcec938d76238975dff9de7d66cfc6e574aa7.1437802102.git.luto@kernel.org>
2015-07-25 9:03 ` [PATCH v4 1/3] x86/ldt: Make modify_ldt synchronous Borislav Petkov
[not found] ` <7286d77aa81abc38dc40362e2439861427064f6f.1437802102.git.luto@kernel.org>
2015-07-25 6:23 ` [PATCH v4 2/3] x86/ldt: Make modify_ldt optional Willy Tarreau
[not found] ` <20150725062343.GA3902@1wt.eu>
2015-07-25 6:44 ` Andy Lutomirski
[not found] ` <CALCETrX0ExTFXVdNthwBRheg4vsffPThVuyn7uAcj_TGwpXgiA@mail.gmail.com>
2015-07-25 7:50 ` Willy Tarreau
[not found] ` <20150725075052.GA3918@1wt.eu>
2015-07-25 13:03 ` [PATCH 4/3] x86/ldt: allow to disable modify_ldt at runtime Willy Tarreau
[not found] ` <20150725130340.GA17257@1wt.eu>
2015-07-25 16:08 ` Andy Lutomirski
[not found] ` <CALCETrV+OB0qxtw5CHaZc5RftuCUax04RxTyi_bt4ZKDJ2GB0g@mail.gmail.com>
2015-07-25 16:33 ` Willy Tarreau
[not found] ` <20150725163356.GD17659@1wt.eu>
2015-07-25 17:42 ` Andy Lutomirski
[not found] ` <CALCETrXeWdugPpAkKhUD=f7ftuYSM5fxaPxnF2=PwygupP2_4w@mail.gmail.com>
2015-07-25 18:45 ` Willy Tarreau [this message]
2015-07-27 19:04 ` Kees Cook
[not found] ` <CAGXu5jJDfnkRG2F=L37CnrgnCN4Yxh0p9QWbYFqQ_Jw5qk3HsQ@mail.gmail.com>
2015-07-27 21:37 ` Willy Tarreau
2015-07-25 9:15 ` [PATCH v4 2/3] x86/ldt: Make modify_ldt optional Borislav Petkov
[not found] ` <20150725091531.GE3427@nazgul.tnic>
2015-07-25 16:03 ` Andy Lutomirski
[not found] ` <CALCETrV_oeS_kA3oNirWTwc00ze2v=QLmx6tZKU7sxt_+gMcAg@mail.gmail.com>
2015-07-25 16:35 ` Willy Tarreau
2015-07-27 15:36 ` [PATCH v4 0/3] x86: modify_ldt improvement, test, and config option Boris Ostrovsky
[not found] ` <55B64FEA.70204@oracle.com>
2015-07-27 15:53 ` Andy Lutomirski
[not found] ` <CALCETrUEYTCwYzA0bvG=EJOi+pdXX=FZXoaQc4tYGkJATM7x3g@mail.gmail.com>
2015-07-27 16:18 ` Boris Ostrovsky
[not found] ` <55B659EC.5030009@oracle.com>
2015-07-28 2:20 ` Andy Lutomirski
[not found] ` <CALCETrV7zVbt0ZV4KYcSTUHjAOxzGmu3SXWoT7iECB=zWSN7Ew@mail.gmail.com>
2015-07-28 3:16 ` Andy Lutomirski
[not found] ` <CALCETrV275oYQY80yg6TJ-h9n2Db-uF-po90bF+JmKjnV5ZqYw@mail.gmail.com>
2015-07-28 3:23 ` Andy Lutomirski
2015-07-28 3:43 ` Boris Ostrovsky
2015-07-28 10:29 ` Andrew Cooper
[not found] ` <55B75993.90909@citrix.com>
2015-07-28 14:05 ` Boris Ostrovsky
[not found] ` <55B78C35.1050702@oracle.com>
2015-07-28 14:35 ` Andrew Cooper
[not found] ` <55B79314.8060009@citrix.com>
2015-07-28 14:50 ` Boris Ostrovsky
[not found] ` <55B796BF.1080005@oracle.com>
2015-07-28 15:15 ` Konrad Rzeszutek Wilk
2015-07-28 15:23 ` Andrew Cooper
[not found] ` <20150728151527.GI26623@x230.dumpdata.com>
2015-07-28 15:39 ` Boris Ostrovsky
[not found] ` <55B79E75.4010000@citrix.com>
2015-07-28 15:59 ` Boris Ostrovsky
2015-07-28 15:43 ` Andy Lutomirski
[not found] ` <CALCETrXt2OP=+JAj7gzUOJT+5=00Qg3Te11twSeK8F_9zn_nwg@mail.gmail.com>
2015-07-28 16:30 ` Andrew Cooper
[not found] ` <55B7AE39.7000101@citrix.com>
2015-07-28 17:07 ` Andy Lutomirski
[not found] ` <CALCETrVd56uwkZw0YtaSHKHp5dh7NugQouigibJkr=e3Q_mYyA@mail.gmail.com>
2015-07-28 17:10 ` Boris Ostrovsky
[not found] ` <55B7B791.2050208@oracle.com>
2015-07-29 0:21 ` Andy Lutomirski
[not found] ` <CALCETrXH5_PMqfH1en_5c+5gUpq8SjCnQ3Xaz-K6ej6FgBgLDQ@mail.gmail.com>
2015-07-29 0:47 ` Andrew Cooper
[not found] ` <55B822B8.3090608@citrix.com>
2015-07-29 3:01 ` Boris Ostrovsky
[not found] ` <55B841FF.2000102@oracle.com>
2015-07-29 4:26 ` Andy Lutomirski
2015-07-29 5:28 ` Andy Lutomirski
[not found] ` <CALCETrWkMRb+Y3FsJ7+kNYmPxtupM3ZPOeOPwagXytgBqM6tJQ@mail.gmail.com>
2015-07-29 14:21 ` Andrew Cooper
[not found] ` <55B8E16C.2050406@citrix.com>
2015-07-29 14:43 ` Boris Ostrovsky
[not found] ` <55B8E68B.2030305@oracle.com>
2015-07-29 19:03 ` Andrew Cooper
[not found] ` <55B9236B.9090507@citrix.com>
2015-07-29 21:23 ` Boris Ostrovsky
[not found] ` <55B94451.8040600@oracle.com>
2015-07-29 21:26 ` Andy Lutomirski
[not found] ` <CALCETrWA=hAyqqp=yzZ2r_S=9U9hLkd6dZEuNefew8hyLVA_eQ@mail.gmail.com>
2015-07-29 21:33 ` Boris Ostrovsky
2015-07-29 21:37 ` Andrew Cooper
[not found] ` <55B947AF.7020404@citrix.com>
2015-07-29 22:05 ` Andy Lutomirski
[not found] ` <CALCETrXp_DV-_Uvekwv7xLHO-5P8Oxkgn6OeXG-6tVOD4RkKMw@mail.gmail.com>
2015-07-29 22:11 ` Andrew Cooper
[not found] ` <55B94F9D.3000405@citrix.com>
2015-07-29 22:40 ` Boris Ostrovsky
2015-07-29 22:46 ` David Vrabel
2015-07-29 22:49 ` Boris Ostrovsky
[not found] ` <55B95863.2000102@oracle.com>
2015-07-29 22:55 ` David Vrabel
2015-07-29 23:02 ` Andrew Cooper
[not found] ` <55B95B70.8010902@citrix.com>
2015-07-29 23:13 ` Andy Lutomirski
[not found] ` <CALCETrWy93qobHmMWzTfqFN+0Y7DGyM7viwpPMGOeSiXEP0Z6w@mail.gmail.com>
2015-07-30 0:29 ` Andrew Cooper
[not found] ` <55B96FE0.6010600@citrix.com>
2015-07-30 18:30 ` Andy Lutomirski
[not found] ` <CALCETrUi2GBdGP2OX+3PwSf0UYjKuf2+DugENe3Y6mUoy-Rfkw@mail.gmail.com>
2015-07-30 18:54 ` Andrew Cooper
[not found] ` <55BA72E1.4050809@citrix.com>
2015-07-30 20:01 ` Boris Ostrovsky
[not found] ` <55BA828E.8070304@oracle.com>
2015-07-30 20:05 ` Andy Lutomirski
[not found] ` <CALCETrUsFn23tKf418VSbGCgXoXXRq8dk41ZfM3F55=_xWPQhw@mail.gmail.com>
2015-07-30 20:18 ` Boris Ostrovsky
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