From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 285F63858D33; Wed, 12 Apr 2023 09:18:47 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 285F63858D33
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1681291127;
	bh=eP4pMGTMq9IKbs549A6a8dwx6EBV/xwl22+alnFMV4M=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=Igb4qvVrUwHB63HqERyo8uSa+04RdWXwAswYG2c7fl5927Qfw0wZNLA5mdYXoQ1Vj
	 aXfM1FOOV8lI51aicyhRLzyOk189M7GvSJZqLttjNVfbmez68GuB1NANDtDlox2T9t
	 X6tzUwVOZr6geMPbGmbkuntcE3hOK27lqAZHT0Qg=
From: "rguenther at suse dot de" <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 09:18:46 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: sanitizer
X-Bugzilla-Version: 8.4.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenther at suse dot de
X-Bugzilla-Status: NEW
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-109446-4-BsVU5TlGvp@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-109446-4@http.gcc.gnu.org/bugzilla/>
References: <bug-109446-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109446

--- Comment #12 from rguenther at suse dot de <rguenther at suse dot de> ---
On Wed, 12 Apr 2023, marxin at gcc dot gnu.org wrote:

> 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 que=
stion is
> > > > why ASAN doesn't instrument the generated aggregate copy?  Maybe be=
cause
> > > > in C/C++ you cannot write an aggregate array copy?
> > >=20
> > > We do instrument those.  But only instrument them by checking the fir=
st and
> > > last byte
> > > of the copy, not all bytes in between (because that would be for inli=
ne
> > > checking too large - we'd need to emit inline a loop over those bytes=
).
> >=20
> > OK, that's lack of an appropriate API then?  But still the first and la=
st
> > 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.

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.=