LLVM Image Activator

[Brooks Davis]

On Sun, Jan 13, 2013 at 12:24:35PM -0800, John-Mark Gurney wrote:
> Nathan Whitehorn wrote this message on Sun, Jan 13, 2013 at 10:14 -0800:
> > On 01/13/13 09:13, Konstantin Belousov wrote:
> > > On Sun, Jan 13, 2013 at 08:21:37AM -0800, Nathan Whitehorn wrote:
> > >> On 01/13/13 05:20, Konstantin Belousov wrote:
> > >>> On Sun, Jan 13, 2013 at 12:41:09PM +0100, Ed Schouten wrote:
> > >>>> Hi Kostik,
> > >>>>
> > >>>> 2013/1/7 Konstantin Belousov <kostikbel at gmail.com>:
> > >>>>> I still do remember the buzz about the binary format 0xCAFEBABE, which
> > >>>>> AFAIR gained image activator support on several OSes, to be garbage
> > >>>>> collected.
> > >>>>
> > >>>> Maybe it would then be a good idea then to add some kind of general
> > >>>> purpose remapping imgact? Example:
> > >>>>
> > >>>> /etc/imgacttab:
> > >>>>
> > >>>> cafebabe /usr/local/bin/java
> > >>>> cffaedfe /usr/local/bin/osx_emulator
> > >>>> 4243c0de /usr/bin/lli
> > >>>>
> > >>>> That way we still give people the freedom to play around with mapping
> > >>>> their own executable formats, but don't need to maintain a bunch of
> > >>>> imgacts.
> > >>>
> > >>> A generic module that could be somewhat customized at runtime to map
> > >>> offset+signature into the shebang path could be a possibility indeed.
> > >>> I strongly prefer to have it as module and not enabled by default.
> > >>>
> > >>> Asking Nathan for writing the thing is too much, IMHO, esp. in
> > >>> the response to the 50-lines hack.
> > >>>
> > >>
> > >> I think this is a good idea, since it both prevents a profusion of
> > >> similar activators and works nicely in jails and similar environments. I
> > >> probably won't write it quickly, but it should not take more than about
> > >> 50 lines, so I can't imagine it will be that bad. There are some
> > >> complications with this kind of design from the things in the XXX
> > >> comment in imgact_llvm.c about handling argv[0] that I need to think
> > >> some more about.
> > > Great. I do not believe in the 50 lines, but I am happy that you want
> > > to work this out.
> > > 
> > >>
> > >> Why are you opposed to having it there by default? I think it's actually
> > >> quite important that it be there by default. Having it not "standard"
> > >> would be fine, but it should at least be in GENERIC. There are minimal
> > >> security risks since it just munges begin_argv and doesn't even load the
> > >> executable and it's little enough code that there should not be any
> > >> kernel bloat to speak of. If things like this aren't enabled by default,
> > >> no one can depend on them being there, no one will use it, and the point
> > >> is entirely lost.
> > > All image activators demonstrated a constant stream of security holes.
> > > Even our ELF activator, and I was guilty there too.
> > > 
> > > I definitely do not fight over the inclusion of the proposed activator
> > > into GENERIC, but do insist on the config option + module.
> > > 
> > 
> > OK, that sounds like a plan then. I'll try to code up something
> > configurable in the next couple weeks, unless someone else beats me to it.
> 
> I'll point out that file already has the magic (pun intended) that we
> are looking for, though I do realize that the code might be a bit much
> to import..

As someone who recently stuffed libmagic into a very constrained sandbox
environment, I can safely assert that you don't want to go there.  The
code isn't written in a way that would make this easy and I definitely
wouldn't want it in the kernel.

-- Brooks
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 188 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/freebsd-toolchain/attachments/20130114/72e970f5/attachment.sig>