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From: Mark Rutland <mark.rutland@arm.com>
To: Laura Abbott <labbott@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	kernel-hardening@lists.openwall.com,
	Catalin Marinas <catalin.marinas@arm.com>,
	Kees Cook <keescook@chromium.org>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [RFC PATCH 0/2] arm64: optional paranoid __{get,put}_user checks
Date: Wed, 1 Nov 2017 12:05:55 +0000	[thread overview]
Message-ID: <20171101120555.yvb65g3wgtxskfh3@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <77c80381-cf68-aa1a-9112-e057c068eeb6@redhat.com>

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

  reply	other threads:[~2017-11-01 12:06 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 [this message]
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
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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