Date: Thu, 08 Apr 2010 07:17:46 -0700 From: Patrick Mahan <mahan@mahan.org> To: freebsd-hackers@freebsd.org Subject: Modifying ELF files Message-ID: <4BBDE58A.9050502@mahan.org>
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In my job, we are producing applications and KLM's for our product
that require them to be signed so that our installer will recognize
and validate our images.
The signature is stored in each app as
unsigned char signature[40] __attribute__((section(".compsign")));
What I need to do is open the file for writing, locate the ".compsign"
section and stuff in the signature, write it out and close the file.
(simple ELF manipulation)
An 'ls -l' shows the following:
% ls compklm.ko
-rw-r--r-- 1 pmahan pmahan 125296 Apr 6 22:50 /home/pmahan/temp/compklm.ko
When I try to run my program
./signfile --signature=A203239897C8EB360D1EB2C84E8E77B16E5B7C9A compklm.ko
open: Text file busy
Googling and looking at the kernel sources, it seems that it detects
this file contains 'shared text', that is, it is an executable file
and does not allow me to open it for writing.
I understand (from my google search) this is a means to keep you from
shooting yourself in the foot. But there has got to be a way and I
really don't want to grovel through the compiler code to find it. I
looked at using libelf.so but it also requires that the file be open
for writing. So I am kinda of stuck. If I cannot find a quick solution
we might need to do all of our signing on our FC11 box which does not
have this issue.
Thanks for the education I always get from this list,
Patrick
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