From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Tue, 20 Nov 2018 00:57:48 +0100 From: Pavel Machek Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c Message-ID: <20181119235748.GC7367@amd> References: <20181109084353.GA5321@dhcp22.suse.cz> <20181113094305.GM15120@dhcp22.suse.cz> <20181113151503.fd370e28cb9df5a0933e9b04@linux-foundation.org> <20181113153204.ea0c0895866838de9e3bc8d0@linux-foundation.org> <1f4439c8-d669-a1ac-53f5-36c04da72a51@suse.cz> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="ZwgA9U+XZDXt4+m+" Content-Disposition: inline In-Reply-To: <1f4439c8-d669-a1ac-53f5-36c04da72a51@suse.cz> Sender: linux-kernel-owner@vger.kernel.org To: Vlastimil Babka Cc: Andrew Morton , Michal Hocko , Kyungtae Kim , pavel.tatashin@microsoft.com, osalvador@suse.de, rppt@linux.vnet.ibm.com, aaron.lu@intel.com, iamjoonsoo.kim@lge.com, alexander.h.duyck@linux.intel.com, mgorman@techsingularity.net, lifeasageek@gmail.com, threeearcat@gmail.com, syzkaller@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Konstantin Khlebnikov List-ID: --ZwgA9U+XZDXt4+m+ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi1 > >>>> --- a/mm/page_alloc.c > >>>> +++ b/mm/page_alloc.c > >>>> @@ -4364,6 +4353,15 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsign= ed int order, int preferred_nid, > >>>> gfp_t alloc_mask; /* The gfp_t that was actually used for allocati= on */ > >>>> struct alloc_context ac =3D { }; > >>>> =20 > >>>> + /* > >>>> + * There are several places where we assume that the order value i= s sane > >>>> + * so bail out early if the request is out of bound. > >>>> + */ > >>>> + if (unlikely(order >=3D MAX_ORDER)) { > >>>> + WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN)); > >>>> + return NULL; > >>>> + } > >>>> + > >>> > >>> I know "everybody enables CONFIG_DEBUG_VM", but given this is fastpat= h, > >>> we could help those who choose not to enable it by using > >>> > >>> #ifdef CONFIG_DEBUG_VM > >>> if (WARN_ON_ONCE(order >=3D MAX_ORDER && !(gfp_mask & __GFP_NOWARN))) > >>> return NULL; > >>> #endif > >> > >> Hmm, but that would mean there's still potential undefined behavior for > >> !CONFIG_DEBUG_VM, so I would prefer not to do it like that. > >> > >=20 > > What does "potential undefined behavior" mean here? >=20 > I mean that it becomes undefined once a caller with order >=3D MAX_ORDER > appears. Worse if it's directly due to a userspace action, like in this > case. We should really check if value from userspace is sane _before_ passing it to alloc_pages(). Anything else is too fragile. Maybe alloc_pages should do the second check, but... Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --ZwgA9U+XZDXt4+m+ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAlvzTfwACgkQMOfwapXb+vJrxQCfQWRQidsCidtn9kylt9QlaV9b HX8AoJNp4zXtXxXm0nbOi7G27O/MZVJy =y6KK -----END PGP SIGNATURE----- --ZwgA9U+XZDXt4+m+--