From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f198.google.com (mail-io0-f198.google.com [209.85.223.198]) by kanga.kvack.org (Postfix) with ESMTP id 6CC786B0005 for ; Mon, 25 Jul 2016 20:22:12 -0400 (EDT) Received: by mail-io0-f198.google.com with SMTP id u25so485170426ioi.1 for ; Mon, 25 Jul 2016 17:22:12 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id l143si13280073iol.251.2016.07.25.17.22.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Jul 2016 17:22:11 -0700 (PDT) Message-ID: <1469492520.30053.123.camel@redhat.com> Subject: Re: [PATCH v4 12/12] mm: SLUB hardened usercopy support From: Rik van Riel Date: Mon, 25 Jul 2016 20:22:00 -0400 In-Reply-To: <9fca8a3c-da82-d609-79bb-4f5a779cbc1b@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> <1469482923.30053.122.camel@redhat.com> <9fca8a3c-da82-d609-79bb-4f5a779cbc1b@redhat.com> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-8qqetdyYF8mCBLlKELUz" 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 --=-8qqetdyYF8mCBLlKELUz Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2016-07-25 at 16:29 -0700, Laura Abbott wrote: > On 07/25/2016 02:42 PM, Rik van Riel wrote: > > 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 ca= che line > > > > usage > > > > =C2=A0 =C2=A0=C2=A0=C2=A0instead of managing queues of cached objec= ts (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->sla= b_cache; > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0object_size =3D= slab_ksize(s); > > >=20 > > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (ptr < page_address(pag= e)) > > > +=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 = within object. */ > > > =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0offset =3D (ptr= - page_address(page)) % s->size; > > >=20 > >=20 > > 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? > >=20 > > Specifically, in patch 3/12: > >=20 > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0page =3D virt_to_head_page(p= tr); > > + > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0/* Check slab allocator for = flags 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); > >=20 > > How can that generate a ptr that is not inside the page? > >=20 > > What am I overlooking?=C2=A0=C2=A0And, should it be in the changelog or > > a comment? :) > >=20 >=20 >=20 > I ran into the subtraction issue when the vmalloc detection wasn't > working on ARM64, somehow virt_to_head_page turned into a page > that happened to have PageSlab set. I agree if everything is working > properly this is redundant but given the type of feature this is, a > little bit of redundancy against a system running off into the weeds > or bad patches might be warranted. >=C2=A0 That's fair. =C2=A0I have no objection to the check, but would like to see it documented, since it does look a little out of place. --=20 All Rights Reversed. --=-8qqetdyYF8mCBLlKELUz 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 iQEcBAABCAAGBQJXlq0pAAoJEM553pKExN6Dv5IIALtZxgoQj8M9YOmCa4BjHZtJ R5FYg7nvY19D598u4s6f88QF92Xf7D7iqkCugZOU6/Te6x54VypAx83ud2zP828U 4qmIudPyyhX+VGlc71cVJ2gy12Xx5G7u9H5/+Qgyp/Y4bxithElDidjQN4VTpS8g 6y4hwd34ADw7ah+yVR65GNIq+eZTdRjH0wTCE0vrcdgl4yCWQ5vm3uv4LzAkbRPH QWRmKt4D5ubSb5cPqK6EnUUc+0SYkydVSNII4DoG+NGNYynklhlptGEFdrrIG/sS Gb++LQw7kb4XrQ2/Jg6jy1yqimXo2OeQ8ZZXo86zz82ByleVjvWRnxsvcHEqk8o= =kQY+ -----END PGP SIGNATURE----- --=-8qqetdyYF8mCBLlKELUz-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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