linux-kernel - Re: [PATCH 1/4] module: add syscall to load module from fd

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Message-ID: <87fw2j5dlj.fsf@rustcorp.com.au>
Date:	Thu, 03 Jan 2013 10:42:24 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Michael Kerrisk <mtk.manpages@...il.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Kees Cook <keescook@...omium.org>,
	linux-kernel@...r.kernel.org,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	jonathon@...masters.org, Michael Kerrisk <mtk.manpages@...il.com>,
	linux-man@...r.kernel.org
Subject: Re: [PATCH 1/4] module: add syscall to load module from fd

Michael Kerrisk <mtk.manpages@...il.com> writes:
> Hi Rusty,

Hi Michael,

> The description here is rather thin. Could you supply a sentence or
> two for each of MODULE_INIT_IGNORE_MODVERSIONS and
> MODULE_INIT_IGNORE_VERMAGIC that would be suitable for the manual
> page?
>
> Thanks,

There are one or two safety checks built into a module, which are
checked to match the kernel on module load.  The first is a "vermagic"
string containing the kernel version number and prominent features (such
as CPU type).  If the module was built with CONFIG_MODVERSIONS set, a
version hash is recorded for each symbol the module uses based on the
types it refers to: in this case, the kernel version number within the
"vermagic" string is ignored, as the symbol version hashes are assumed
to be sufficiently reliable.

Using the MODULE_INIT_IGNORE_VERMAGIC flag indicates that the vermagic
is to be ignored, and the MODULE_INIT_IGNORE_MODVERSIONS flag indicates
that the version hashes are to be ignored.  If the kernel is built to
permit such forced loading (ie. CONFIG_MODULE_FORCE_LOAD is set) then
loading will continue, otherwise it will fail with ENOEXEC as expected
for malformed modules.

Hope that is more usable?

Thanks,
Rusty,
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