linux-kernel - Re: livepatch: reuse module loader code to write relocations

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] [day] [month] [year] [list]

Message-ID: <20151221055742.GB22850@packer-debian-8-amd64.digitalocean.com>
Date:	Mon, 21 Dec 2015 00:57:42 -0500
From:	Jessica Yu <jeyu@...hat.com>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Jonathan Corbet <corbet@....net>,
	Miroslav Benes <mbenes@...e.cz>, linux-api@...r.kernel.org,
	live-patching@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: livepatch: reuse module loader code to write relocations

+++ Petr Mladek [17/12/15 16:45 +0100]:
>On Wed 2015-12-16 00:40:48, Jessica Yu wrote:
>> Turns out the string parsing stuff, even with the help of lib/string.c, doesn't
>> look very pretty. As I'm working on v3, I'm starting to think having
>> klp_write_object_relocations() loop simply through all the elf sections might
>> not be a good idea. Let me explain.
>>
>> I don't like the amount of string manipulation code that would potentially come
>> with this change. Even with a string as simple as ".klp.rela.objname", we'll
>> end up with a bunch of kstrdup's/kmalloc's and kfree's (unless we modify and
>> chop the section name string in place, which I don't think we should do) that
>> are going to be required at every iteration of the loop, all just to be able to
>> call strcmp() and see if we're dealing with a klp rela section that belongs to
>> the object in question. This also leads to more complicated error handling.
>
>I do not think that we need to allocate and free buffers every time
>we compare a substring.
>
>One possibility is to find the position of the substring using
>strchr(). Then you could compare it using strncmp() and pass there
>the pointer where the substring begins.

Hm, yes you're right. Specifically, it looks like strcspn() would also
be useful for this situation (i.e. calculate the length of a substring
that does not contain certain characters); combined with strncmp(),
this should make the string code much simpler, and no more buffer
allocating/freeing. :-)

Jessica
--
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/