linux-kernel - Re: Regression - locking (all from 2.6.28)

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: <20090306192812.GA26767@elf.ucw.cz>
Date:	Fri, 6 Mar 2009 20:28:12 +0100
From:	Pavel Machek <pavel@....cz>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	jan sonnek <ha2nny@...il.com>, linux-kernel@...r.kernel.org,
	viro@...iv.linux.org.uk, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andy Whitcroft <apw@...dowen.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: Regression - locking (all from 2.6.28)

Hi!

On Fri 2009-03-06 11:19:46, Dave Hansen wrote:
> On Fri, 2009-03-06 at 18:00 +0000, Catalin Marinas wrote:
> > > I think you should be more worried about consistency rather than missing
> > > entries.  Take these two lines of code:
> > > 
> > >       start_pfn = node->node_start_pfn;
> > >       /* hotplug occurs here */
> > >       end_pfn = start_pfn + node->node_spanned_pages;
> > > 
> > > What if someone comes in and adds memory to the node, at the beginning
> > > of the node, after you have calculated start_pfn?  Try to think of what
> > > value you'll get for end_pfn and whether it is consistent and was *ever*
> > > valid at all.  Would that oops the kernel?
> > 
> > I assume pfn_valid() should handle this and kmemleak wouldn't scan the
> > page, unless we need locks around pfn_valid as well but I haven't seen
> > any used in the kernel.
> 
> You assume incorrectly. :(
> 
> Take my above example, and assume that you have two nodes which are
> right next to each other.  You might run over the end of one node and
> into the next one.  Your pages will be pfn_valid() but you will be on
> the wrong node.
> 
> Please take a look at those locks that I mentioned.  Notice that they
> are lock the pgdat *span*, not the validity of pages inside the pgdat.
> Your code deals with what pages the pgdats *span* and thus needs that
> lock.  Notice that my example also had to do with those two lines of
> code incorrectly guessing the pgdat's *span*.
> 
> We recently went to some pain to make sure that the software suspend
> code (which walks pgdat ranges as well) worked with memory hotplug.
> There really isn't that much code around that actually cares at runtime
> about which physical areas a particular node or zone spans.  Yours is a
> rarity and will require some caution.
> 
> You could probably also use the memory hotplug mutex found here:
> 
> https://lists.linux-foundation.org/pipermail/linux-pm/2008-November/018884.html
> 
> But I'm not sure where those patches have gone.  Hmmm.  Pavel?

I don't think they were applied. They probably should... Rafael was
about to look into that, but he lost the patch pointer.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
--
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/