execve-type memory-based function, possible?

["Jørgen P. Tjernø"]

Hi!

I've recently been toying with methods for copy-protection and other
esoteric subjects, for academic and hobby purposes, and I haven't found
much info on this subject.

I want to see if it's possible (from userspace) to load and execute an
ELF-binary based on a memory-buffer, i.e. load, relocate, etcetera (then
execute) a program that's stored in memory.

I can't find any readily available options, I've toyed a bit with shmem
(to get an fd) and fexecve, but haven't gotten far. I've briefly looked
at the execve-code in the kernel.

So I'm curious; does anyone have any experience or suggestions on this
subject? Is it at all possible to do the operations via usermode? I've
toyed with creating copy-protection-schemes and binary packers and such
under Win32, where it's possible, but I have no experience on the
subject under Linux (or found any documentation on anyone else doing so).

Any papers, links, source-file-references etcetera would be appreciated. :-)

--
Kindest regards / Med vennlig hilsen,
  Jørgen P. Tjernø
  <jorgen@...>
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["Jørgen P. Tjernø"]

Jørgen P. Tjernø wrote:
 > [ .. a lot of stuff .. ]

It might've been a bit unclear, so here goes:

I'm thinking something like if you read the contents of the file
"/bin/ls" into a buffer, and then want to execute that.
Wouldn't that require that you allocate the memory, do relocation, set
the correct memory page protection (to execute for code, etc), etcetera?

--
Kindest regards / Med vennlig hilsen,
  Jørgen P. Tjernø
  <jorgen@...>
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[Steve Graegert]

On 10/23/06, "Jørgen P. Tjernø" <jorgen@...> wrote:
> Jørgen P. Tjernø wrote:
>  > [ .. a lot of stuff .. ]
>
> It might've been a bit unclear, so here goes:
>
> I'm thinking something like if you read the contents of the file
> "/bin/ls" into a buffer, and then want to execute that.
> Wouldn't that require that you allocate the memory, do relocation, set
> the correct memory page protection (to execute for code, etc), etcetera?

Jørgen,

(now I got it)  Looks like you'd want to implement some kind of
userland exec.  In this case the following archive will be useful:
http://www.graegert.com/code/ul_exec-v1.1.tar.gz.  Although quite
dated it illustrates basic concepts.

If you have questions about the code or the general approach, feel
free to contact me privately.

        \Steve

--

Steve Grägert <steve@...>
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Internet  http://eth0.graegert.com, http://blog.graegert.com
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