From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f70.google.com (mail-lf0-f70.google.com [209.85.215.70]) by kanga.kvack.org (Postfix) with ESMTP id 80ACD6B0253 for ; Sat, 9 Jul 2016 08:58:26 -0400 (EDT) Received: by mail-lf0-f70.google.com with SMTP id l89so1093096lfi.3 for ; Sat, 09 Jul 2016 05:58:26 -0700 (PDT) Received: from mail-lf0-f43.google.com (mail-lf0-f43.google.com. [209.85.215.43]) by mx.google.com with ESMTPS id m8si1195603lfb.157.2016.07.09.05.58.24 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 09 Jul 2016 05:58:24 -0700 (PDT) Received: by mail-lf0-f43.google.com with SMTP id l188so43438604lfe.2 for ; Sat, 09 Jul 2016 05:58:24 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1467843928-29351-1-git-send-email-keescook@chromium.org> From: Laura Abbott Date: Sat, 9 Jul 2016 05:58:22 -0700 Message-ID: Subject: Re: [PATCH 0/9] mm: Hardened usercopy Content-Type: multipart/alternative; boundary=001a114b0e5c7a84e80537337986 Sender: owner-linux-mm@kvack.org List-ID: To: Ard Biesheuvel Cc: Kees Cook , "linux-kernel@vger.kernel.org" , Rik van Riel , Casey Schaufler , PaX Team , Brad Spengler , Russell King , Catalin Marinas , Will Deacon , 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 , Laura Abbott , "linux-arm-kernel@lists.infradead.org" , "linux-ia64@vger.kernel.org" , linuxppc-dev , sparclinux@vger.kernel.org, "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , kernel-hardening@lists.openwall.com --001a114b0e5c7a84e80537337986 Content-Type: text/plain; charset=UTF-8 On Sat, Jul 9, 2016 at 1:25 AM, Ard Biesheuvel wrote: > On 9 July 2016 at 04:22, Laura Abbott wrote: > > On 07/06/2016 03:25 PM, Kees Cook wrote: > >> > >> Hi, > >> > >> This is a start of the mainline port of PAX_USERCOPY[1]. After I started > >> writing tests (now in lkdtm in -next) for Casey's earlier port[2], I > >> kept tweaking things further and further until I ended up with a whole > >> new patch series. To that end, I took Rik's feedback and made a number > >> of other changes and clean-ups as well. > >> > >> Based on my understanding, PAX_USERCOPY was designed to catch a few > >> classes of flaws around the use of copy_to_user()/copy_from_user(). > These > >> changes don't touch get_user() and put_user(), since these operate on > >> constant sized lengths, and tend to be much less vulnerable. There > >> are effectively three distinct protections in the whole series, > >> each of which I've given a separate CONFIG, though this patch set is > >> only the first of the three intended protections. (Generally speaking, > >> PAX_USERCOPY covers what I'm calling CONFIG_HARDENED_USERCOPY (this) and > >> CONFIG_HARDENED_USERCOPY_WHITELIST (future), and PAX_USERCOPY_SLABS > covers > >> CONFIG_HARDENED_USERCOPY_SPLIT_KMALLOC (future).) > >> > >> This series, which adds CONFIG_HARDENED_USERCOPY, checks that objects > >> being copied to/from userspace meet certain criteria: > >> - if address is a heap object, the size must not exceed the object's > >> allocated size. (This will catch all kinds of heap overflow flaws.) > >> - if address range is in the current process stack, it must be within > the > >> current stack frame (if such checking is possible) or at least > entirely > >> within the current process's stack. (This could catch large lengths > that > >> would have extended beyond the current process stack, or overflows if > >> their length extends back into the original stack.) > >> - if the address range is part of kernel data, rodata, or bss, allow it. > >> - if address range is page-allocated, that it doesn't span multiple > >> allocations. > >> - if address is within the kernel text, reject it. > >> - everything else is accepted > >> > >> The patches in the series are: > >> - The core copy_to/from_user() checks, without the slab object checks: > >> 1- mm: Hardened usercopy > >> - Per-arch enablement of the protection: > >> 2- x86/uaccess: Enable hardened usercopy > >> 3- ARM: uaccess: Enable hardened usercopy > >> 4- arm64/uaccess: Enable hardened usercopy > >> 5- ia64/uaccess: Enable hardened usercopy > >> 6- powerpc/uaccess: Enable hardened usercopy > >> 7- sparc/uaccess: Enable hardened usercopy > >> - The heap allocator implementation of object size checking: > >> 8- mm: SLAB hardened usercopy support > >> 9- mm: SLUB hardened usercopy support > >> > >> Some notes: > >> > >> - This is expected to apply on top of -next which contains fixes for the > >> position of _etext on both arm and arm64. > >> > >> - I couldn't detect a measurable performance change with these features > >> enabled. Kernel build times were unchanged, hackbench was unchanged, > >> etc. I think we could flip this to "on by default" at some point. > >> > >> - The SLOB support extracted from grsecurity seems entirely broken. I > >> have no idea what's going on there, I spent my time testing SLAB and > >> SLUB. Having someone else look at SLOB would be nice, but this series > >> doesn't depend on it. > >> > >> Additional features that would be nice, but aren't blocking this series: > >> > >> - Needs more architecture support for stack frame checking (only x86 > now). > >> > >> > > > > Even with the SLUB fixup I'm still seeing this blow up on my arm64 > system. > > This is a > > Fedora rawhide kernel + the patches > > > > [ 0.666700] usercopy: kernel memory exposure attempt detected from > > fffffc0008b4dd58 () (8 bytes) > > [ 0.666720] CPU: 2 PID: 79 Comm: modprobe Tainted: G W > > 4.7.0-0.rc6.git1.1.hardenedusercopy.fc25.aarch64 #1 > > [ 0.666733] Hardware name: AppliedMicro Mustang/Mustang, BIOS 1.1.0 Nov > 24 > > 2015 > > [ 0.666744] Call trace: > > [ 0.666756] [] dump_backtrace+0x0/0x1e8 > > [ 0.666765] [] show_stack+0x24/0x30 > > [ 0.666775] [] dump_stack+0xa4/0xe0 > > [ 0.666785] [] __check_object_size+0x6c/0x230 > > [ 0.666795] [] create_elf_tables+0x74/0x420 > > [ 0.666805] [] load_elf_binary+0x828/0xb70 > > [ 0.666814] [] search_binary_handler+0xb4/0x240 > > [ 0.666823] [] do_execveat_common+0x63c/0x950 > > [ 0.666832] [] do_execve+0x3c/0x50 > > [ 0.666841] [] > call_usermodehelper_exec_async+0xe8/0x148 > > [ 0.666850] [] ret_from_fork+0x10/0x50 > > > > This happens on every call to execve. This seems to be the first > > copy_to_user in > > create_elf_tables. I didn't get a chance to debug and I'm going out of > town > > all of next week so all I have is the report unfortunately. config > attached. > > > > This is a known issue, and a fix is already queued for v4.8 in the arm64 > tree: > > 9fdc14c55c arm64: mm: fix location of _etext [0] > > which moves _etext up in the linker script so that it does not cover > .rodata > > ARM was suffering from the same problem, and Kees proposed a fix for > it. I don't know what the status of that patch is, though. > > Note that on arm64, we have > > #define ELF_PLATFORM ("aarch64") > > which explains why k_platform points into .rodata in this case. On > ARM, it points to a writable string (as the code quoted by Rik shows), > so there it will likely explode elsewhere without the linker script > fix. > > [0] > https://git.kernel.org/cgit/linux/kernel/git/arm64/linux.git/commit/?h=for-next/core&id=9fdc14c55c > > -- > Ard. > Ugh, I completely missed that note about the patch on arm64. Sorry for the noise. Thanks, Laura --001a114b0e5c7a84e80537337986 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Sat, Jul 9, 2016 at 1:25 AM,= Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
On 9 July 2016 at 04:22, Laura A= bbott <labbott@r= edhat.com> wrote:
> On 07/06/2016 03:25 PM, Kees Cook wrote:
>>
>> Hi,
>>
>> This is a start of the mainline port of PAX_USERCOPY[1]. After I s= tarted
>> writing tests (now in lkdtm in -next) for Casey's earlier port= [2], I
>> kept tweaking things further and further until I ended up with a w= hole
>> new patch series. To that end, I took Rik's feedback and made = a number
>> of other changes and clean-ups as well.
>>
>> Based on my understanding, PAX_USERCOPY was designed to catch a fe= w
>> classes of flaws around the use of copy_to_user()/copy_from_user()= . These
>> changes don't touch get_user() and put_user(), since these ope= rate on
>> constant sized lengths, and tend to be much less vulnerable. There=
>> are effectively three distinct protections in the whole series, >> each of which I've given a separate CONFIG, though this patch = set is
>> only the first of the three intended protections. (Generally speak= ing,
>> PAX_USERCOPY covers what I'm calling CONFIG_HARDENED_USERCOPY = (this) and
>> CONFIG_HARDENED_USERCOPY_WHITELIST (future), and PAX_USERCOPY_SLAB= S covers
>> CONFIG_HARDENED_USERCOPY_SPLIT_KMALLOC (future).)
>>
>> This series, which adds CONFIG_HARDENED_USERCOPY, checks that obje= cts
>> being copied to/from userspace meet certain criteria:
>> - if address is a heap object, the size must not exceed the object= 's
>>=C2=A0 =C2=A0allocated size. (This will catch all kinds of heap ove= rflow flaws.)
>> - if address range is in the current process stack, it must be wit= hin the
>>=C2=A0 =C2=A0current stack frame (if such checking is possible) or = at least entirely
>>=C2=A0 =C2=A0within the current process's stack. (This could ca= tch large lengths that
>>=C2=A0 =C2=A0would have extended beyond the current process stack, = or overflows if
>>=C2=A0 =C2=A0their length extends back into the original stack.) >> - if the address range is part of kernel data, rodata, or bss, all= ow it.
>> - if address range is page-allocated, that it doesn't span mul= tiple
>>=C2=A0 =C2=A0allocations.
>> - if address is within the kernel text, reject it.
>> - everything else is accepted
>>
>> The patches in the series are:
>> - The core copy_to/from_user() checks, without the slab object che= cks:
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A01- mm: Hardened usercopy
>> - Per-arch enablement of the protection:
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A02- x86/uaccess: Enable hardened u= sercopy
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A03- ARM: uaccess: Enable hardened = usercopy
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A04- arm64/uaccess: Enable hardened= usercopy
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A05- ia64/uaccess: Enable hardened = usercopy
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A06- powerpc/uaccess: Enable harden= ed usercopy
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A07- sparc/uaccess: Enable hardened= usercopy
>> - The heap allocator implementation of object size checking:
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A08- mm: SLAB hardened usercopy sup= port
>>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A09- mm: SLUB hardened usercopy sup= port
>>
>> Some notes:
>>
>> - This is expected to apply on top of -next which contains fixes f= or the
>>=C2=A0 =C2=A0position of _etext on both arm and arm64.
>>
>> - I couldn't detect a measurable performance change with these= features
>>=C2=A0 =C2=A0enabled. Kernel build times were unchanged, hackbench = was unchanged,
>>=C2=A0 =C2=A0etc. I think we could flip this to "on by default= " at some point.
>>
>> - The SLOB support extracted from grsecurity seems entirely broken= . I
>>=C2=A0 =C2=A0have no idea what's going on there, I spent my tim= e testing SLAB and
>>=C2=A0 =C2=A0SLUB. Having someone else look at SLOB would be nice, = but this series
>>=C2=A0 =C2=A0doesn't depend on it.
>>
>> Additional features that would be nice, but aren't blocking th= is series:
>>
>> - Needs more architecture support for stack frame checking (only x= 86 now).
>>
>>
>
> Even with the SLUB fixup I'm still seeing this blow up on my arm64= system.
> This is a
> Fedora rawhide kernel + the patches
>
> [ 0.666700] usercopy: kernel memory exposure attempt detected from
> fffffc0008b4dd58 (<kernel text>) (8 bytes)
> [ 0.666720] CPU: 2 PID: 79 Comm: modprobe Tainted: G=C2=A0 =C2=A0 =C2= =A0 =C2=A0 W
> 4.7.0-0.rc6.git1.1.hardenedusercopy.fc25.aarch64 #1
> [ 0.666733] Hardware name: AppliedMicro Mustang/Mustang, BIOS 1.1.0 No= v 24
> 2015
> [ 0.666744] Call trace:
> [ 0.666756] [<fffffc0008088a20>] dump_backtrace+0x0/0x1e8
> [ 0.666765] [<fffffc0008088c2c>] show_stack+0x24/0x30
> [ 0.666775] [<fffffc0008455344>] dump_stack+0xa4/0xe0
> [ 0.666785] [<fffffc000828d874>] __check_object_size+0x6c/0x230<= br> > [ 0.666795] [<fffffc00083a5748>] create_elf_tables+0x74/0x420 > [ 0.666805] [<fffffc00082fb1f0>] load_elf_binary+0x828/0xb70
> [ 0.666814] [<fffffc0008298b4c>] search_binary_handler+0xb4/0x24= 0
> [ 0.666823] [<fffffc0008299864>] do_execveat_common+0x63c/0x950<= br> > [ 0.666832] [<fffffc0008299bb4>] do_execve+0x3c/0x50
> [ 0.666841] [<fffffc00080e3720>] call_usermodehelper_exec_async+= 0xe8/0x148
> [ 0.666850] [<fffffc0008084a80>] ret_from_fork+0x10/0x50
>
> This happens on every call to execve. This seems to be the first
> copy_to_user in
> create_elf_tables. I didn't get a chance to debug and I'm goin= g out of town
> all of next week so all I have is the report unfortunately. config att= ached.
>

This is a known issue, and a fix is already queued for v4.8 in = the arm64 tree:

9fdc14c55c arm64: mm: fix location of _etext [0]

which moves _etext up in the linker script so that it does not cover .rodat= a

ARM was suffering from the same problem, and Kees proposed a fix for
it. I don't know what the status of that patch is, though.

Note that on arm64, we have

=C2=A0 #define ELF_PLATFORM=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ("= ;aarch64")

which explains why k_platform points into .rodata in this case. On
ARM, it points to a writable string (as the code quoted by Rik shows),
so there it will likely explode elsewhere without the linker script
fix.

[0] https://git.kernel.org/cgit/linux/kernel/git/arm64/linux.git/co= mmit/?h=3Dfor-next/core&id=3D9fdc14c55c

--
Ard.

Ugh, I completely missed that no= te about the patch on arm64. Sorry for the noise.

Thanks,
Laura --001a114b0e5c7a84e80537337986-- -- 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