linux-kernel - Re: [PATCH] "killing" sg

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: <4728569D.9080502@panasas.com>
Date:	Wed, 31 Oct 2007 12:19:09 +0200
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Jens Axboe <jens.axboe@...cle.com>, linux-ide@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] "killing" sg_last(), and discussion

On Wed, Oct 31 2007 at 10:49 +0200, Jeff Garzik <jeff@...zik.org> wrote:
> I looked into killing sg_last(), but really, this is the best its gonna
> get (moving sg_last to libata-core.c).
> 
> You could maybe kill one use with caching, but in the other sg_last()
> callsites there isn't another s/g loop we can stick a "last_sg = sg;"
> into.
> 
> libata is stuck because we undertake the highly unusual operation of
> fiddling with the final S/G element, to enforce 32-bit alignment.
> 
> Of course we could eliminate all that nasty fiddling/padding
> completely, including sg_last(), if other areas of the kernel would
> guarantee ahead of time that buffer lengths are always a multiple
> of 4........
> 
> 	Jeff
> 
OK Now I'm confused. I thought that ULD's can give you SG's 
that are actually longer than bufflen and that, at the end, the 
bufflen should govern the transfer length.

Now FS_PC commands are sector aligned so you do not have
problems with that.

The BLOCK_PC commands have 2 main sources that I know of
one is sg && bsg from user mode that can easily enforce
4 bytes alignment. The second is kernel services which 80%
of these are done by scsi_execute(). All These can be found
and fixed. Starting with scsi_execute(). Another place can be
blk_rq_map_sg(), since all IO's are bio based. It can enforce 
alignment too.

I would start by sticking a WARN_ON(qc->pad_len) and
see if it triggers, what are the sources of that.

Please note that the code already has a 4 bytes alignment
assumption about the start of the transfer, other wise
the first SG can also have a none aligned length, which
is not checked for.

Boaz
-
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/