From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@kernel.org>
Cc: "security@kernel.org" <security@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
X86 ML <x86@kernel.org>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
xen-devel <xen-devel@lists.xen.org>,
Jan Beulich <jbeulich@suse.com>,
Sasha Levin <sasha.levin@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v4 2/3] x86/ldt: Make modify_ldt optional
Date: Sat, 25 Jul 2015 11:15:31 +0200 [thread overview]
Message-ID: <20150725091531.GE3427__4307.28176511383$1437815821$gmane$org@nazgul.tnic> (raw)
In-Reply-To: <7286d77aa81abc38dc40362e2439861427064f6f.1437802102.git.luto@kernel.org>
On Fri, Jul 24, 2015 at 10:36:45PM -0700, Andy Lutomirski wrote:
> The modify_ldt syscall exposes a large attack surface and is
> unnecessary for modern userspace. Make it optional.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/Kconfig | 17 +++++++++++++++++
> arch/x86/include/asm/mmu.h | 2 ++
> arch/x86/include/asm/mmu_context.h | 31 +++++++++++++++++++++++--------
> arch/x86/kernel/Makefile | 3 ++-
> arch/x86/kernel/cpu/perf_event.c | 4 ++++
> arch/x86/kernel/process_64.c | 2 ++
> arch/x86/kernel/step.c | 2 ++
> kernel/sys_ni.c | 1 +
> 8 files changed, 53 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index b3a1a5d77d92..ede52be845db 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1015,6 +1015,7 @@ config VM86
> config X86_16BIT
> bool "Enable support for 16-bit segments" if EXPERT
> default y
> + depends on MODIFY_LDT_SYSCALL
> ---help---
> This option is required by programs like Wine to run 16-bit
> protected mode legacy code on x86 processors. Disabling
> @@ -2053,6 +2054,22 @@ config CMDLINE_OVERRIDE
> This is used to work around broken boot loaders. This should
> be set to 'N' under normal conditions.
>
> +config MODIFY_LDT_SYSCALL
> + bool "Enable the LDT (local descriptor table)" if EXPERT
bool "Enable modify_ldt() for per-process Local Descriptor Table"
is how I'd call it.
> + default y
Is that "default y" going to turn into a "default n" after a grace
period?
> + ---help---
> + Linux can allow user programs to install a per-process x86
> + Local Descriptor Table (LDT) using the modify_ldt(2) system
> + call. This is required to run 16-bit or segmented code such as
> + DOSEMU or some Wine programs. It is also used by some very old
> + threading libraries.
> +
> + Enabling this feature adds a small amount of overhead to
> + context switches and increases the low-level kernel attack
> + surface. Disabling it removes the modify_ldt(2) system call.
> +
> + Saying 'N' here may make sense for embedded or server kernels.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
--
next prev parent reply other threads:[~2015-07-25 9:15 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
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 ` Borislav Petkov [this message]
[not found] ` <20150725091531.GE3427@nazgul.tnic>
2015-07-25 16:03 ` [PATCH v4 2/3] x86/ldt: Make modify_ldt optional 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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