From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f72.google.com (mail-it0-f72.google.com [209.85.214.72]) by kanga.kvack.org (Postfix) with ESMTP id DA64F6B025E for ; Mon, 25 Jul 2016 17:42:15 -0400 (EDT) Received: by mail-it0-f72.google.com with SMTP id j124so211419397ith.1 for ; Mon, 25 Jul 2016 14:42:15 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id c84si22203621iod.42.2016.07.25.14.42.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Jul 2016 14:42:15 -0700 (PDT) Message-ID: <1469482923.30053.122.camel@redhat.com> Subject: Re: [PATCH v4 12/12] mm: SLUB hardened usercopy support From: Rik van Riel Date: Mon, 25 Jul 2016 17:42:03 -0400 In-Reply-To: <0f980e84-b587-3d9e-3c26-ad57f947c08b@redhat.com> References: <1469046427-12696-1-git-send-email-keescook@chromium.org> <1469046427-12696-13-git-send-email-keescook@chromium.org> <0f980e84-b587-3d9e-3c26-ad57f947c08b@redhat.com> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-4nNy0NdtJWS4930kcKBo" Mime-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Laura Abbott , Kees Cook , kernel-hardening@lists.openwall.com Cc: Laura Abbott , Balbir Singh , Daniel Micay , Josh Poimboeuf , Casey Schaufler , PaX Team , Brad Spengler , Russell King , Catalin Marinas , Will Deacon , Ard Biesheuvel , Benjamin Herrenschmidt , Michael Ellerman , Tony Luck , Fenghua Yu , "David S. Miller" , x86@kernel.org, Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Andy Lutomirski , Borislav Petkov , Mathias Krause , Jan Kara , Vitaly Wool , Andrea Arcangeli , Dmitry Vyukov , linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org --=-4nNy0NdtJWS4930kcKBo Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2016-07-25 at 12:16 -0700, Laura Abbott wrote: > On 07/20/2016 01:27 PM, Kees Cook wrote: > > Under CONFIG_HARDENED_USERCOPY, this adds object size checking to > > the > > SLUB allocator to catch any copies that may span objects. Includes > > a > > redzone handling fix discovered by Michael Ellerman. > >=20 > > Based on code from PaX and grsecurity. > >=20 > > Signed-off-by: Kees Cook > > Tested-by: Michael Ellerman > > --- > > =C2=A0init/Kconfig |=C2=A0=C2=A01 + > > =C2=A0mm/slub.c=C2=A0=C2=A0=C2=A0=C2=A0| 36 +++++++++++++++++++++++++++= +++++++++ > > =C2=A02 files changed, 37 insertions(+) > >=20 > > diff --git a/init/Kconfig b/init/Kconfig > > index 798c2020ee7c..1c4711819dfd 100644 > > --- a/init/Kconfig > > +++ b/init/Kconfig > > @@ -1765,6 +1765,7 @@ config SLAB > >=20 > > =C2=A0config SLUB > > =C2=A0 bool "SLUB (Unqueued Allocator)" > > + select HAVE_HARDENED_USERCOPY_ALLOCATOR > > =C2=A0 help > > =C2=A0 =C2=A0=C2=A0=C2=A0SLUB is a slab allocator that minimizes cache = line > > usage > > =C2=A0 =C2=A0=C2=A0=C2=A0instead of managing queues of cached objects (= SLAB > > approach). > > diff --git a/mm/slub.c b/mm/slub.c > > index 825ff4505336..7dee3d9a5843 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -3614,6 +3614,42 @@ void *__kmalloc_node(size_t size, gfp_t > > flags, int node) > > =C2=A0EXPORT_SYMBOL(__kmalloc_node); > > =C2=A0#endif > >=20 > > +#ifdef CONFIG_HARDENED_USERCOPY > > +/* > > + * Rejects objects that are incorrectly sized. > > + * > > + * Returns NULL if check passes, otherwise const char * to name of > > cache > > + * to indicate an error. > > + */ > > +const char *__check_heap_object(const void *ptr, unsigned long n, > > + struct page *page) > > +{ > > + struct kmem_cache *s; > > + unsigned long offset; > > + size_t object_size; > > + > > + /* Find object and usable object size. */ > > + s =3D page->slab_cache; > > + object_size =3D slab_ksize(s); > > + > > + /* Find offset within object. */ > > + offset =3D (ptr - page_address(page)) % s->size; > > + > > + /* Adjust for redzone and reject if within the redzone. */ > > + if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE) { > > + if (offset < s->red_left_pad) > > + return s->name; > > + offset -=3D s->red_left_pad; > > + } > > + > > + /* Allow address range falling entirely within object > > size. */ > > + if (offset <=3D object_size && n <=3D object_size - offset) > > + return NULL; > > + > > + return s->name; > > +} > > +#endif /* CONFIG_HARDENED_USERCOPY */ > > + >=20 > I compared this against what check_valid_pointer does for SLUB_DEBUG > checking. I was hoping we could utilize that function to avoid > duplication but a) __check_heap_object needs to allow accesses > anywhere > in the object, not just the beginning b) accessing page->objects > is racy without the addition of locking in SLUB_DEBUG. >=20 > Still, the ptr < page_address(page) check from __check_heap_object > would > be good to add to avoid generating garbage large offsets and trying > to > infer C math. >=20 > diff --git a/mm/slub.c b/mm/slub.c > index 7dee3d9..5370e4f 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -3632,6 +3632,9 @@ const char *__check_heap_object(const void > *ptr, unsigned long n, > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0s =3D page->slab_ca= che; > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0object_size =3D sla= b_ksize(s); > =C2=A0=C2=A0 > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (ptr < page_address(page)) > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0return s->name; > + > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0/* Find offset with= in object. */ > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0offset =3D (ptr - p= age_address(page)) % s->size; >=C2=A0 I don't get it, isn't that already guaranteed because we look for the page that ptr is in, before __check_heap_object is called? Specifically, in patch 3/12: +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0page =3D virt_to_head_page(ptr); + +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0/* Check slab allocator for flag= s and size. */ +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (PageSlab(page)) +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0return __check_heap_object(ptr, n, page); How can that generate a ptr that is not inside the page? What am I overlooking? =C2=A0And, should it be in the changelog or a comment? :) --=20 All Rights Reversed. --=-4nNy0NdtJWS4930kcKBo Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAABCAAGBQJXloesAAoJEM553pKExN6DQ10H/j1zT06MVuOCz6p/bB+kEVn1 eqrh2adrHpfOL7vsnrXm6VoGwgcHYPohW2t+tIEDlwI72rnj0bFJ+yULZAru9BDD f9+PZHtdKXr5MmZANCFyNTn6y8paSvbEzj4KhMFkOuR1cMYtgk5X37ta8HxgW8g+ aR+FgPxUO0iONyxSp+2hercLK9+xuWZ6u4JBRfrZ5jL7HxoOWlSP+e3+X0UMW0jZ TmyzQeirSi3d0486aEyPql2I825w3MmX9ujFtHkdFZbQGrD4PeVDcd8MLyGn+4w0 QG1CopRBEnmO2Aaz8dXs5HaA+LfzYMrzwzravXcCmZLN9AR5BpYaszTabSe/LzE= =hTcV -----END PGP SIGNATURE----- --=-4nNy0NdtJWS4930kcKBo-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org