linux-kernel - Re: JIT emulator needs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:	Thu, 21 Jun 2007 13:08:36 +0200
From:	Bodo Eggert <7eggert@....de>
To:	Albert Cahalan <acahalan@...il.com>,
	William Lee Irwin III <wli@...omorphy.com>,
	linux-kernel@...r.kernel.org
Subject: Re: JIT emulator needs

Albert Cahalan <acahalan@...il.com> wrote:
> On 6/19/07, William Lee Irwin III <wli@...omorphy.com> wrote:
>> On Fri, Jun 08, 2007 at 02:35:22AM -0400, Albert Cahalan wrote:

>>> Right now, Linux isn't all that friendly to JIT emulators.
>>> Here are the problems and suggestions to improve the situation.
>>> There is an SE Linux execmem restriction that enforces W^X.
>>> Assuming you don't wish to just disable SE Linux, there are
>>> two ugly ways around the problem. You can mmap a file twice,
>>> or you can abuse SysV shared memory. The mmap method requires
>>> that you know of a filesystem mounted rw,exec where you can
>>> write a very large temporary file. This arbitrary filesystem,
>>> rather than swap space, will be the backing store. The SysV
>>> shared memory method requires an undocumented flag and is
>>> subject to some annoying size limits. Both methods create
>>> objects that will fail to be deleted if the program dies
>>> before marking the objects for deletion.
>>
>> If the policy forbidding self-modifying code lacks a method of
>> exempting programs such as JIT interpreters (which I doubt) then
>> it's a problem. I'm with Alan on this one.
> 
> It does and it doesn't. There is not a reasonable way for a
> user to mark an app as needing full self-modifying ability.
> It's not like the executable stack, which can be set via the
> ELF note markings on the executable. (ELF note markings are
> ideal because they can not be used via a ret-to-libc attack)
> 
> With admin privs, one can change SE Linux settings. Mark the
> executable, disable the protection system-wide, generate a
> completely new SE Linux policy, or just turn SE Linux off.

According to the documents I found about SELinux, you can also
 - create a this-app-needs-selfmodification type
 - allow users to change the context type of their files to this type
 - configure a domain to allow self-modification
 - configure the domain transition

Brave words from someone who did not yet successfully find the magic in
order to install the refpolicy on debilian (after finding their refpolicy-foo
to be incomplete and their refpolicy-src to not compile).
-- 
Why do women have smaller feet than men?
It's one of those "evolutionary things" that allows them to stand
closer to the kitchen sink.
Friß, Spammer: Jy@...xq.7eggert.dyndns.org d-afnhbe@....7eggert.dyndns.org
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/