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From: "xry111 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug sanitizer/109446] Possible destination array overflow without
 diagnosis in memcpy
Date: Wed, 12 Apr 2023 11:16:14 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109446

--- Comment #13 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #12)
> On Wed, 12 Apr 2023, marxin at gcc dot gnu.org wrote:
>=20
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109446
> >=20
> > --- Comment #9 from Martin Li?ka <marxin at gcc dot gnu.org> ---
> > (In reply to Richard Biener from comment #8)
> > > (In reply to Jakub Jelinek from comment #7)
> > > > (In reply to Richard Biener from comment #6)
> > > > > not sure if we should prevent all of those transforms.  But the q=
uestion is
> > > > > why ASAN doesn't instrument the generated aggregate copy?  Maybe =
because
> > > > > in C/C++ you cannot write an aggregate array copy?
> > > >=20
> > > > We do instrument those.  But only instrument them by checking the f=
irst and
> > > > last byte
> > > > of the copy, not all bytes in between (because that would be for in=
line
> > > > checking too large - we'd need to emit inline a loop over those byt=
es).
> > >=20
> > > OK, that's lack of an appropriate API then?  But still the first and =
last
> > > byte should be sufficient to detect the problem (but maybe I'm missing
> > > something here).
> >=20
> > No, because the last byte is out of redzone:
> >=20
> > =3D>0x7ffff5300000: f1 f1 f1 f1 00 00 00[f3]f3 f3 f3 f3 00 00 00 00
> >=20
> > the 'f3' redzone is covering 5*8 bytes after the data type only.
>=20
> OK, so it's lack of an API then.  The alternative would be to
> do sth similar to stack-checking - instrument every 5*8 byte,
> possibly up to some limit.  Or, as you probably suggest, avoid
> folding memcpy with size larger than 5*8 byte inline.

I guess doing so will need to change the cpymemM expand of all targets.=