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Message-ID: <b113b487-acc6-24b8-d58c-425d3c884f4c@redhat.com>
Date: Fri, 8 Jul 2016 19:22:50 -0700
From: Laura Abbott <labbott@...hat.com>
To: Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Cc: Rik van Riel <riel@...hat.com>, Casey Schaufler <casey@...aufler-ca.com>,
PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon
<will.deacon@....com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Michael Ellerman <mpe@...erman.id.au>, Tony Luck <tony.luck@...el.com>,
Fenghua Yu <fenghua.yu@...el.com>, "David S. Miller" <davem@...emloft.net>,
x86@...nel.org, Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski
<luto@...nel.org>, Borislav Petkov <bp@...e.de>,
Mathias Krause <minipli@...glemail.com>, Jan Kara <jack@...e.cz>,
Vitaly Wool <vitalywool@...il.com>, Andrea Arcangeli <aarcange@...hat.com>,
Dmitry Vyukov <dvyukov@...gle.com>, Laura Abbott
<labbott@...oraproject.org>, linux-arm-kernel@...ts.infradead.org,
linux-ia64@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
sparclinux@...r.kernel.org, linux-arch@...r.kernel.org, linux-mm@...ck.org,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 0/9] mm: Hardened usercopy
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.
Thanks,
Laura
View attachment "hardened_copy_config" of type "text/plain" (162541 bytes)
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