From: Kees Cook <keescook@chromium.org>
To: Laura Abbott <labbott@redhat.com>
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 15:28:29 -0700 [thread overview]
Message-ID: <CAGXu5j+eb+41XRorgAVURKEsixiMYgtcmpKwQzJ3Mct_yw1G6Q@mail.gmail.com> (raw)
In-Reply-To: <0f2d5f89-2939-06ec-9b59-b19f828d8968@redhat.com>
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
--
Kees Cook
Pixel Security
next prev parent reply other threads:[~2017-11-01 22:28 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 [this message]
2017-11-01 23:05 ` Laura Abbott
2017-11-01 23:29 ` Kees Cook
2017-11-02 1:25 ` Laura Abbott
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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