From: keescook@chromium.org (Kees Cook)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 0/9] mm: Hardened usercopy
Date: Sat, 9 Jul 2016 10:03:24 -0700 [thread overview]
Message-ID: <CAGXu5jJLH9kSxiR9=pHnHvv00UCJRCcrB_Juj=9ROyDxB0wK6A@mail.gmail.com> (raw)
In-Reply-To: <CAKv+Gu_F03ncqT2wWFte2bFWQ7tSruL0ZaxTBLT9_NEs-1SioQ@mail.gmail.com>
On Sat, Jul 9, 2016 at 1:25 AM, Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
> On 9 July 2016 at 04:22, Laura Abbott <labbott@redhat.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 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 (<kernel text>) (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] [<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
>> [ 0.666795] [<fffffc00083a5748>] create_elf_tables+0x74/0x420
>> [ 0.666805] [<fffffc00082fb1f0>] load_elf_binary+0x828/0xb70
>> [ 0.666814] [<fffffc0008298b4c>] search_binary_handler+0xb4/0x240
>> [ 0.666823] [<fffffc0008299864>] do_execveat_common+0x63c/0x950
>> [ 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 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
Oops, I missed this reply, sorry for the redundant answer. :)
> 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.
This is also in -next "ARM: 8583/1: mm: fix location of _etext".
> 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
-Kees
--
Kees Cook
Chrome OS & Brillo Security
next prev parent reply other threads:[~2016-07-09 17:03 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-06 22:25 [PATCH 0/9] mm: Hardened usercopy Kees Cook
2016-07-06 22:25 ` [PATCH 1/9] " Kees Cook
2016-07-07 5:37 ` Baruch Siach
2016-07-07 17:25 ` Kees Cook
2016-07-07 18:35 ` Baruch Siach
2016-07-07 7:42 ` Thomas Gleixner
2016-07-07 17:29 ` Kees Cook
2016-07-07 19:34 ` Thomas Gleixner
2016-07-07 8:01 ` Arnd Bergmann
2016-07-07 17:37 ` Kees Cook
2016-07-08 9:22 ` Arnd Bergmann
2016-07-07 16:19 ` Rik van Riel
2016-07-07 16:35 ` Rik van Riel
2016-07-07 17:41 ` Kees Cook
2016-07-06 22:25 ` [PATCH 2/9] x86/uaccess: Enable hardened usercopy Kees Cook
2016-07-06 22:25 ` [PATCH 3/9] ARM: uaccess: " Kees Cook
2016-07-06 22:25 ` [PATCH 4/9] arm64/uaccess: " Kees Cook
2016-07-07 10:07 ` Mark Rutland
2016-07-07 17:19 ` Kees Cook
2016-07-06 22:25 ` [PATCH 5/9] ia64/uaccess: " Kees Cook
2016-07-06 22:25 ` [PATCH 6/9] powerpc/uaccess: " Kees Cook
2016-07-06 22:25 ` [PATCH 7/9] sparc/uaccess: " Kees Cook
2016-07-06 22:25 ` [PATCH 8/9] mm: SLAB hardened usercopy support Kees Cook
2016-07-06 22:25 ` [PATCH 9/9] mm: SLUB " Kees Cook
2016-07-07 7:30 ` [PATCH 0/9] mm: Hardened usercopy Christian Borntraeger
2016-07-07 17:27 ` Kees Cook
2016-07-08 8:46 ` Ingo Molnar
2016-07-08 16:19 ` Linus Torvalds
2016-07-08 18:23 ` Ingo Molnar
[not found] ` <b113b487-acc6-24b8-d58c-425d3c884f4c@redhat.com>
2016-07-09 2:44 ` Rik van Riel
2016-07-09 7:55 ` Ingo Molnar
2016-07-09 8:25 ` Ard Biesheuvel
2016-07-09 17:03 ` Kees Cook [this message]
2016-07-09 17:01 ` Kees Cook
2016-07-09 21:27 ` Andy Lutomirski
2016-07-09 23:16 ` PaX Team
2016-07-10 9:16 ` Ingo Molnar
2016-07-10 12:03 ` PaX Team
2016-07-10 12:38 ` Andy Lutomirski
2016-07-11 18:40 ` Kees Cook
2016-07-11 18:34 ` Kees Cook
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