linux-kernel - Re: [PATCH v4 2/3] mm/page_alloc.c: add config option to sanitize freed pages

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Message-ID: <20150518130213.GA771@amd>
Date:	Mon, 18 May 2015 15:02:13 +0200
From:	Pavel Machek <pavel@....cz>
To:	Anisse Astier <anisse@...ier.eu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	David Rientjes <rientjes@...gle.com>,
	Alan Cox <gnomes@...rguk.ukuu.org.uk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
	Kees Cook <keescook@...omium.org>,
	Andi Kleen <andi@...stfloor.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, linux-mm@...ck.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/3] mm/page_alloc.c: add config option to sanitize
 freed pages

On Mon 2015-05-18 14:41:19, Anisse Astier wrote:
> On Mon, May 18, 2015 at 1:21 PM, Pavel Machek <pavel@....cz> wrote:
> > On Thu 2015-05-14 16:19:47, Anisse Astier wrote:
> >> This new config option will sanitize all freed pages. This is a pretty
> >> low-level change useful to track some cases of use-after-free, help
> >> kernel same-page merging in VM environments, and counter a few info
> >> leaks.
> >
> > Could you document the "few info leaks"? We may want to fix them for
> > !SANTIZE_FREED_PAGES case, too...
> >
> 
> I wish I could; I'd be sending patches for those info leaks, too.
> 
> What I meant is that this feature can also be used as a general
> protection mechanism against a certain class of info leaks; for
> example, some drivers allocating pages that were previously used by
> other subsystems, and then sending structures to userspace that
> contain padding or uninitialized fields, leaking kernel pointers.
> Having all pages cleared unconditionally can help a bit in some cases
> (hence "a few"), but it's of course not an end-all solution.

Ok. So there is class of errors where this helps, but you are not
aware of any such errors in kernel, so you can't fix them... Right?

> I'll edit the commit and kconfig messages to be more precise.

Thanks,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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