I need to modify the ELF loader's kernel implementation of an Ubuntu 14.04 distribution. Having downloaded the sources using:
sudo apt-get source linux-image-$(uname -r)
I ran the configuration script:
make config
in the root source tree. After a seemingly endless sequence of input requests, the script created the .config file needed to build the kernel(or a set of modules). The kernel version I am using is linux-3.13.0 and has the following source tree layout:
$ ls
arch COPYING crypto Documentation dropped.txt FileSystemMakefile fs init Kbuild kernel MAINTAINERS mm README samples security sound ubuntu virt
block CREDITS debian.master drivers elf.dat firmware include ipc Kconfig lib Makefile net REPORTING-BUGS scripts shortcuts tools usr
The ELF loader is located in /path/to/source/fs/binfmt_elf.c. Following this question,in order to compile an individual module it is sufficient to run
make /path/to/module/directory
In this case that would be:
make ./path/to/source/fs
The compilation is quite lengthy; it takes about twenty minutes(on a virtual machine) and the output is written(by default) in the same directory in which the module is located. I've found the object files by running:
find . -name "*.o"
in /path/to/source/fs. Filtering by name the ELF loader can be located by running:
find . -name "*elf*.o"
In the current sources it is written(by default) in:
/path/to/source/fs/binfmt_elf.o
Having gone through this tutorial, I've noticed that kernel modules have the naming convention [module_name].ko in order to distinguish them from user space object files.
My question is how can I insert the new(modified) ELF loader into the kernel given that the current ELF loader is present(as unloading it may prevent binaries from being executed)?
Edit #1:
Running lsmod gives:
$ lsmod
Module Size Used by
nls_utf8 12557 1
isofs 39835 1
vboxsf 39690 0
snd_intel8x0 38153 2
snd_ac97_codec 130285 1 snd_intel8x0
ac97_bus 12730 1 snd_ac97_codec
snd_pcm 102099 2 snd_ac97_codec,snd_intel8x0
snd_page_alloc 18710 2 snd_intel8x0,snd_pcm
snd_seq_midi 13324 0
snd_seq_midi_event 14899 1 snd_seq_midi
rfcomm 69160 0
snd_rawmidi 30144 1 snd_seq_midi
bnep 19624 2
bluetooth 391196 10 bnep,rfcomm
snd_seq 61560 2 snd_seq_midi_event,snd_seq_midi
snd_seq_device 14497 3 snd_seq,snd_rawmidi,snd_seq_midi
snd_timer 29482 2 snd_pcm,snd_seq
joydev 17381 0
snd 69238 12 snd_ac97_codec,snd_intel8x0,snd_timer,snd_pcm,snd_seq,snd_rawmidi,snd_seq_device,snd_seq_midi
serio_raw 13462 0
vboxguest 248441 7 vboxsf
i2c_piix4 22155 0
soundcore 12680 1 snd
mac_hid 13205 0
parport_pc 32701 0
ppdev 17671 0
vboxvideo 12658 0
drm 303102 1 vboxvideo
lp 17759 0
parport 42348 3 lp,ppdev,parport_pc
hid_generic 12548 0
usbhid 52570 0
hid 106148 2 hid_generic,usbhid
psmouse 106678 0
ahci 25819 2
libahci 32560 1 ahci
e1000 145174 0
Which module needs to be compiled as a LKM in order to include the ELF loader. By default the loader is built into the base kernel.
Best Answer
Try this:
How do I build a single in-tree kernel module?
Alternatively, the way I normally do this is something like the following. This is from memory and may or may not work for you. It also builds all the modules.
Install current kernel source:
Some devices need to be added the module name to /etc/modules if it doesn't get automatically loaded.