linux-kernel - Re: [PATCH] add hook to read_from_oldmem() to check for non-ram pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20110506123019.80461d5d.akpm@linux-foundation.org>
Date:	Fri, 6 May 2011 12:30:19 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Olaf Hering <olaf@...fle.de>
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org
Subject: Re: [PATCH] add hook to read_from_oldmem() to check for non-ram
 pages

On Fri, 6 May 2011 12:55:46 +0200
Olaf Hering <olaf@...fle.de> wrote:

> Should the called code increase/decrease the modules refcount instead?
> I remember there was some MODULE_INC/MODULE_DEC macro (cant remember the
> exact name) at some point. What needs to be done inside the module to
> prevent an unload while its still in use? Is it __module_get/module_put
> for each call of fn()? 

A try_module_get(THIS_MODULE) in the register function will do the trick.
However it's unneeded.  Documentation/DocBook/kernel-hacking.tmpl tells us

try_module_get() module_put()

    These manipulate the module usage count, to protect against
    removal (a module also can't be removed if another module uses one
    of its exported symbols: see below).  Before calling into module
    code, you should call <function>try_module_get()</function> on
    that module: if it fails, then the module is being removed and you
    should act as if it wasn't there.  Otherwise, you can safely enter
    the module, and call <function>module_put()</function> when you're
    finished.

So as your module will have a reference to vmcore.c's register and unregister
functions, nothing needs to be done: the presence of the client module alone
will pin the vmcore.c module.

However it's all moot, because the fs/proc/vmcore.c code cannot
presently be built as a module and it's rather unlikely that it ever
will be.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/