Re: [PATCH v3 2/4] PM / Hibernate: prepare for SANITIZE_FREED_PAGES

["PaX Team" <pageexec@freemail.hu>]

On 11 May 2015 at 9:59, Anisse Astier wrote:

> > Otherwise it looks good to me... if the sanitization is considered
> > useful. Did it catch some bugs in the past?
> >
> 
> I've read somewhere that users of grsecurity claim that it caught bugs
> in some drivers, but I haven't verified that personally; it's probably
> much less useful than kasan (or even the original grsec feature) as a
> bug-catcher since it doesn't clear freed slab buffers.

the PaX SANITIZE feature wasn't developed for catching use-after-free bugs
but to help reduce data lifetime from the kernel while not killing too much
performance (this is why i was reluctant to add a finer grained version to
do slab object sanitization until Mathias Krause came up with a workable
compromise).

another reason page zeroing isn't good at catching these bugs is that the
0 fill value will produce NULL pointers which are often explicitly handled
already. on the other hand changing the fill value would not allow the
__GFP_ZERO performance optimization (the slab sanitization feature is a
different story however, we have a non-0 fill value and it keeps triggering
use-after-free bugs).

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