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Date: Tue, 14 Feb 2017 11:07:39 -0800
From: Kees Cook <keescook@...omium.org>
To: Laura Abbott <labbott@...hat.com>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: Format string gcc-plugin?
On Tue, Feb 14, 2017 at 10:01 AM, Laura Abbott <labbott@...hat.com> wrote:
> Hi,
>
> The recent discussions about %pk led me to start playing around
> with writing a gcc plugin (notes about writing a gcc plugin are
> forthcoming). My idea was to expand checking of the kernel's additional
> formats (%pK, %pR etc.) or possibly even change the format
> strings. The big issue is that most of vsprintf.c would end up
> in the plugin which would be ugly to maintain. This concept could
> be used for some of the problems with kernel pointer leaks
> https://kernsec.org/wiki/index.php/Bug_Classes/Kernel_pointer_leak
> but I'm interested if anyone else has thoughts or ideas about
> how better to do this (or even not to do this).
If we can leverage common code between the plugin and vsprintf.c, it
should be doable. I haven't looked at processing format strings at
all, though I assume the plugin would need to check the
__printf-generated attributes.
In my related notes was a hint that looking at how gcc does it
normally is gcc/c-family/c-format.c:
http://stackoverflow.com/a/16336175
And while not strictly part of format type checking, I talked a bit
about dealing with const strings here:
http://www.openwall.com/lists/kernel-hardening/2016/12/07/16
-Kees
--
Kees Cook
Pixel Security
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