From: Laura Abbott <labbott@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
linux-arm-kernel@lists.infradead.org,
LKML <linux-kernel@vger.kernel.org>,
kernel-hardening@lists.openwall.com,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks
Date: Wed, 1 Nov 2017 18:25:53 -0700 [thread overview]
Message-ID: <dd734498-7b03-005c-647b-eec66479cfa1@redhat.com> (raw)
In-Reply-To: <CAGXu5jLhU7si5d3=e5ixhh67fY+6ZGJQBnLxQLMFfcZsB8GJvg@mail.gmail.com>
On 11/01/2017 04:29 PM, Kees Cook wrote:
> On Wed, Nov 1, 2017 at 4:05 PM, Laura Abbott <labbott@redhat.com> wrote:
>> On 11/01/2017 03:28 PM, Kees Cook wrote:
>>> On Wed, Nov 1, 2017 at 2:13 PM, Laura Abbott <labbott@redhat.com> 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!
>
> Awesome! :)
>
> I wonder how hard it might be to make this happen on x86 too (or
> generically). Hmmm
x86 looks like it needs the same ptr_argument fixup as arm64 but
seems to have a separate unsafe path so it's actually easier to
fix up. I have version of this that seems to work so I'll clean
it up and send it out tomorrow.
Thanks,
Laura
next prev parent reply other threads:[~2017-11-02 1:26 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-26 9:09 [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks Mark Rutland
2017-10-26 9:09 ` [RFC PATCH 1/2] arm64: write __range_ok() in C Mark Rutland
2017-11-16 15:28 ` Will Deacon
2017-11-20 12:22 ` Mark Rutland
2017-10-26 9:09 ` [RFC PATCH 2/2] arm64: allow paranoid __{get,put}user Mark Rutland
2017-10-27 15:41 ` [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks Will Deacon
2017-10-27 20:44 ` Mark Rutland
2017-10-28 8:47 ` Russell King - ARM Linux
2017-10-31 23:56 ` Laura Abbott
2017-11-01 12:05 ` Mark Rutland
2017-11-01 21:13 ` Laura Abbott
2017-11-01 22:28 ` Kees Cook
2017-11-01 23:05 ` Laura Abbott
2017-11-01 23:29 ` Kees Cook
2017-11-02 1:25 ` Laura Abbott [this message]
2017-11-03 23:04 ` [RFC PATCH 1/2] x86: Avoid multiple evaluations in __{get,put}_user_size Laura Abbott
2017-11-03 23:04 ` [RFC PATCH 2/2] x86: Allow paranoid __{get,put}_user Laura Abbott
2017-11-04 0:14 ` Kees Cook
2017-11-04 0:24 ` Al Viro
2017-11-04 0:44 ` Al Viro
2017-11-04 1:39 ` Kees Cook
2017-11-04 1:41 ` Kees Cook
2017-11-04 1:58 ` Mark Rutland
2017-11-06 20:38 ` Laura Abbott
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