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Message-ID: <CAGXu5jKnv_mP1hGEe5FbLV_mYknCknZJjo=-Po0mjnWJSV7+_Q@mail.gmail.com>
Date: Wed, 8 Nov 2017 17:11:23 -0800
From: Kees Cook <keescook@...omium.org>
To: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: kernel-hardening@...ts.openwall.com, LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC 0/6] some compile- and run-time format checking
On Wed, Nov 8, 2017 at 2:30 PM, Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
> Consider these strictly RFC/POC.
>
> I tried resurrecting my format_template plugin from two years ago, and
> it rebased pretty cleanly. It also compiles with gcc 6.3, and has the
> expected effect when one tries to trigger it, so it seems to work ok
> (I think there was some build bot issue back then, maybe there still
> is).
>
> The last four patches are something I threw together rather quickly.
> They compile and the few test cases pass, but I obviously need to find
> some places to actually use fmtcheck() to see if it's worth adding.
>
> Rasmus Villemoes (6):
> plugins: implement format_template attribute
> compiler.h: add __format_template
Could you split these two off and send separately? This seems like a
fine thing to get in now. Probably the second patch should be split up
between adding __format_template, and additions of its usage. Do you
have any good ways to find and extract all the dynamic format strings
we need to mark?
> compiler.h: add __attribute__((format_arg)) shorthand
> lib/vsprintf.c: add fmtcheck utility
> kernel.h: implement fmtmatch() wrapper around fmtcheck()
> lib/test_printf.c: add a few fmtcheck() test cases
I like this approach a lot. Combined with checking if a format string
is in read-only memory, this could really close the door on format
string exposures.
Thanks!
-Kees
>
> arch/Kconfig | 18 ++
> drivers/hwmon/applesmc.c | 2 +-
> drivers/staging/speakup/spk_types.h | 2 +-
> include/linux/compiler-gcc.h | 1 +
> include/linux/compiler.h | 10 +
> include/linux/kernel.h | 13 ++
> include/linux/smpboot.h | 2 +-
> include/linux/usb.h | 2 +-
> lib/test_printf.c | 41 ++++
> lib/vsprintf.c | 63 +++++
> scripts/Makefile.gcc-plugins | 2 +
> scripts/gcc-plugins/format_template_plugin.c | 331 +++++++++++++++++++++++++++
> 12 files changed, 483 insertions(+), 4 deletions(-)
> create mode 100644 scripts/gcc-plugins/format_template_plugin.c
>
> --
> 2.11.0
>
--
Kees Cook
Pixel Security
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