From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933837AbdKAXFr (ORCPT ); Wed, 1 Nov 2017 19:05:47 -0400 Received: from mail-ot0-f195.google.com ([74.125.82.195]:55008 "EHLO mail-ot0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933307AbdKAXFp (ORCPT ); Wed, 1 Nov 2017 19:05:45 -0400 X-Google-Smtp-Source: ABhQp+Q/Vij1G/x1MWWyTuPE/+f2l0tLiYUfxrJeb0LYHY2l6oO0a6Suq6TP6Ag/a3l7vdePhNUyNA== Subject: Re: [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks To: Kees Cook Cc: Mark Rutland , linux-arm-kernel@lists.infradead.org, LKML , kernel-hardening@lists.openwall.com, Catalin Marinas , Will Deacon References: <20171026090942.7041-1-mark.rutland@arm.com> <77c80381-cf68-aa1a-9112-e057c068eeb6@redhat.com> <20171101120555.yvb65g3wgtxskfh3@lakrids.cambridge.arm.com> <0f2d5f89-2939-06ec-9b59-b19f828d8968@redhat.com> From: Laura Abbott Message-ID: <57fa4bef-9540-6fb1-b2a7-5bf8b01c748a@redhat.com> Date: Wed, 1 Nov 2017 16:05:41 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/01/2017 03:28 PM, Kees Cook wrote: > On Wed, Nov 1, 2017 at 2:13 PM, Laura Abbott wrote: >> On 11/01/2017 05:05 AM, Mark Rutland wrote: >>> On Tue, Oct 31, 2017 at 04:56:39PM -0700, Laura Abbott wrote: >>>> On 10/26/2017 02:09 AM, Mark Rutland wrote: >>>>> In Prague, Kees mentioned that it would be nice to have a mechanism to >>>>> catch bad __{get,put}_user uses, such as the recent CVE-2017-5123 [1,2] >>>>> issue with unsafe_put_user() in waitid(). >>>>> >>>>> These patches allow an optional access_ok() check to be dropped in >>>>> arm64's __{get,put}_user() primitives. These will then BUG() if a bad >>>>> user pointer is passed (which should only happen in the absence of an >>>>> earlier access_ok() check). >>> >>>> Turning on the option fails as soon as we hit userspace. On my buildroot >>>> based environment I get the help text for ld.so (????) and then a message >>>> about attempting to kill init. >>> >>> Ouch. Thanks for the report, and sorry about this. >>> >>> The problem is that I evaluate the ptr argument twice in >>> __{get,put}_user(), and this may have side effects. >>> >>> e.g. when the ELF loader does things like: >>> >>> __put_user((elf_addr_t)p, sp++) >>> >>> ... we increment sp twice, and write to the wrong user address, leaving >>> sp corrupt. >>> >>> I have an additional patch [1] to fix this, which is in my >>> arm64/access-ok branch [2]. >>> >>> Thanks, >>> Mark. >>> >>> [1] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/commit/?h=arm64/access-ok&id=ebb7ff83eb53b8810395d5cf48712a4ae6d678543 >>> [2] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/access-ok >>> >> >> Thanks, the updated patch works. I wrote an LKDTM test to verify >> the expected behavior (__{get,put}_user panic whereas {get,put}_user >> do not). You're welcome to add Tested-by or I can wait for v2. > > Nice. :) Out of curiosity, can you check if this correctly BUG()s on a > waitid() call when the fixes are reverted? > > 96ca579a1ecc ("waitid(): Avoid unbalanced user_access_end() on > access_ok() error") > 1c9fec470b81 ("waitid(): Add missing access_ok() checks") > > -Kees > Yep, we get a nice bug: [ 34.783912] ------------[ cut here ]------------ [ 34.784484] kernel BUG at kernel/exit.c:1614! [ 34.785016] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP [ 34.785572] Modules linked in: [ 34.786177] CPU: 0 PID: 1324 Comm: a.out Not tainted 4.14.0-rc5-00005-ga3bb7b0f72d3 #69 [ 34.786657] Hardware name: linux,dummy-virt (DT) [ 34.787093] task: ffff80003c4ed400 task.stack: ffff00000ade0000 [ 34.788196] PC is at SyS_waitid+0x1d4/0x210 [ 34.788534] LR is at SyS_waitid+0x20/0x210 [ 34.788839] pc : [] lr : [] pstate: a0000145 [ 34.789310] sp : ffff00000ade3e00 [ 34.789578] x29: ffff00000ade3e00 x28: ffff80003c4ed400 [ 34.790039] x27: ffff0000089e1000 x26: 000000000000005f [ 34.790397] x25: 0000000000000124 x24: 0000000000000015 [ 34.790649] x23: 0000000080000000 x22: 0000ffffb1eb6b24 [ 34.790897] x21: 00000000ffffffff x20: 000080003600c000 [ 34.791149] x19: ffff800000000000 x18: 0000000000000007 [ 34.791397] x17: 0000000000000001 x16: 0000000000000019 [ 34.791648] x15: 0000000000000033 x14: 000000000000004c [ 34.791903] x13: 0000000000000068 x12: ffff000008af69d0 [ 34.792156] x11: ffff00000ade3c20 x10: 0000000000000000 [ 34.792451] x9 : 0000000000000000 x8 : 0000000000000000 [ 34.792706] x7 : 0000000000000000 x6 : ffff000008f42f18 [ 34.792965] x5 : dead000000000100 x4 : 0000000000000011 [ 34.793214] x3 : ffff80003c4ed400 x2 : ffff800000000004 [ 34.793462] x1 : 0001000000000000 x0 : 0000000000000000 [ 34.793743] Process a.out (pid: 1324, stack limit = 0xffff00000ade0000) [ 34.794098] Call trace: [ 34.794351] Exception stack(0xffff00000ade3cc0 to 0xffff00000ade3e00) [ 34.794722] 3cc0: 0000000000000000 0001000000000000 ffff800000000004 ffff80003c4ed400 [ 34.795034] 3ce0: 0000000000000011 dead000000000100 ffff000008f42f18 0000000000000000 [ 34.795297] 3d00: 0000000000000000 0000000000000000 0000000000000000 ffff00000ade3c20 [ 34.795549] 3d20: ffff000008af69d0 0000000000000068 000000000000004c 0000000000000033 [ 34.795803] 3d40: 0000000000000019 0000000000000001 0000000000000007 ffff800000000000 [ 34.796066] 3d60: 000080003600c000 00000000ffffffff 0000ffffb1eb6b24 0000000080000000 [ 34.796277] 3d80: 0000000000000015 0000000000000124 000000000000005f ffff0000089e1000 [ 34.796477] 3da0: ffff80003c4ed400 ffff00000ade3e00 ffff0000080cdc68 ffff00000ade3e00 [ 34.796677] 3dc0: ffff0000080cde1c 00000000a0000145 0000000000000000 ffff80003c4ed400 [ 34.796884] 3de0: 0001000000000000 dead000000000100 ffff00000ade3e00 ffff0000080cde1c [ 34.797153] [] SyS_waitid+0x1d4/0x210 [ 34.797298] Exception stack(0xffff00000ade3ec0 to 0xffff00000ade4000) [ 34.797470] 3ec0: 0000000000000000 0000000000000000 ffff800000000000 0000000000000004 [ 34.797670] 3ee0: 0000000000000000 0400000055550400 0000ffffb1e0a011 0000000000000cbf [ 34.797873] 3f00: 000000000000005f 0000000000000a3b 0000000000000000 16170f120a1a1311 [ 34.798073] 3f20: 00000000000001a8 0000ffffb1f8ecb8 0000ffffb1e1c0e0 0000000000000002 [ 34.798272] 3f40: 0000ffffb1eb6af0 0000000000420018 0000000000000000 0000000000400740 [ 34.798471] 3f60: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 34.798668] 3f80: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 34.798870] 3fa0: 0000000000000000 0000fffff7294200 00000000004006fc 0000fffff7294200 [ 34.799068] 3fc0: 0000ffffb1eb6b24 0000000080000000 0000000000000000 000000000000005f [ 34.799265] 3fe0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 34.799474] [] el0_svc_naked+0x24/0x28 [ 34.799715] Code: f9400fb4 17ffff9a d503201f f9000fb4 (d4210000) [ 34.800121] ---[ end trace a14ca5cd5d8f9b30 ]---