linux-kernel - RE: [PATCH v2 1/2] mm, kasan: improve double-free detection

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Date:	Mon, 9 May 2016 06:04:28 +0000
From:	"Luruo, Kuthonuzo" <kuthonuzo.luruo@....com>
To:	Dmitry Vyukov <dvyukov@...gle.com>,
	Yury Norov <ynorov@...iumnetworks.com>
CC:	"aryabinin@...tuozzo.com" <aryabinin@...tuozzo.com>,
	"glider@...gle.com" <glider@...gle.com>,
	"cl@...ux.com" <cl@...ux.com>,
	"penberg@...nel.org" <penberg@...nel.org>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"klimov.linux@...il.com" <klimov.linux@...il.com>
Subject: RE: [PATCH v2 1/2] mm, kasan: improve double-free detection

> >> Thank you for the review!
> >>
> >> > > + switch (alloc_data.state) {
> >> > > + case KASAN_STATE_QUARANTINE:
> >> > > + case KASAN_STATE_FREE:
> >> > > +         kasan_report((unsigned long)object, 0, false,
> >> > > +                         (unsigned long)__builtin_return_address(1));
> >> >
> >> > __builtin_return_address() is unsafe if argument is non-zero. Use
> >> > return_address() instead.
> >>
> >> hmm, I/cscope can't seem to find an x86 implementation for
> return_address().
> >> Will dig further; thanks.
> >>
> >
> > It seems there's no generic interface to obtain return address. x86
> > has  working __builtin_return_address() and it's ok with it, others
> > use their own return_adderss(), and ok as well.
> >
> > I think unification is needed here.
> 
> 
> We use _RET_IP_ in other places in portable part of kasan.

Yeah, _RET_IP_ is the way to go here.

Not directly related but: while looking into kasan_slab_free() callers, it seems
to me that, with SLAB + quarantine, kasan_poison_kfree() should _not_ be
calling into kasan_slab_free(). The intent in the call-chain thru
kasan_poison_kree() seems to be only to poison object shadow, not actually
free it.

Alexander, can you please comment/confirm? Thanks.

Kuthonuzo