COMPEL(1) CRIU Manual COMPEL(1)
NAME
compel - Execute parasitic code within another process.
SYNOPSIS
compel hgen [option ...]
compel plugins [PLUGIN_NAME ...]
compel [--compat] includes | cflags | ldflags
compel [--compat] [--static] libs
DESCRIPTION
compel is a utility to execute arbitrary code, also called parasite
code, in the context of a foreign process. The parasitic code, once
compiled with compel flags and packed, can be executed in the context
of other tasks. Currently there is only one way to load the parasitic
blob into victim task using libcompel.a, called c-header.
ARGUMENTS
Positional Arguments
hgen
create a header from the .po file, which is the parasite binary.
plugins
prints the plugins available.
ldflags
prints the ldflags available to compel during linking of parasite
code.
cflags
prints the compel cflags to be used during compilation of parasitic
code.
includes
prints list of standard include directories.
libs
prints list of static or dynamic libraries that compel can link
with.
OPTIONS
-f, --file FILE
Path to the binary file, FILE, which compel must turn into a header
-o, --output FILE
Path to the header file, FILE, where compel must write the result-
ing header.
-p, --prefix NAME
Specify prefix for var names
-l, --log-level NUM
Default log level of compel.
-h, --help
Prints usage and exits.
-V, --version
Prints version number of compel.
SOURCE EXAMPLES
Parasitic Code
#include <compel/plugins/std.h>
int parasite_trap_cmd(int cmd, void *args); //gets called by com-
pel_run_in_thread()
int parasite_daemon_cmd(int cmd, void *arg); // gets called by com-
pel_rpc_call() and compel_rpc_call_sync()
void parasite_cleanup(void); //gets called on parasite unload by com-
pel_cure()
Infecting code
The parasitic code is compiled and converted to a header using compel,
and included here.
#include <compel/infect.h>
#include "parasite.h"
Following steps are performed to infect the victim process:
• stop the task: int compel_stop_task(int pid);
• prepare infection handler: struct parasite_ctl *compel_prepare(int
pid);
• execute system call: int compel_syscall(ctl, int syscall_nr, long
*ret, int arg ...);
• infect victim: int compel_infect(ctl, nr_thread,
size_of_args_area);
• cure the victim: int compel_cure(ctl); //ctl pointer is freed by
this call
• Resume victim: int compel_resume_task(pid, orig_state, state);
ctl must be configured with blob information by calling PRE-
FIX_setup_c_header(), with ctl as its argument. PREFIX is the argument
given to -p when calling hgen, else it is deduced from file name.
EXAMPLES
To generate a header file(.h) from a parasite binary file(.po) use:
compel hgen -f parasite.po -o parasite.h
parasite.po file is obtained by compiling the parasite source with com-
pel flags and linking it with the compel plugins.
AUTHOR
The CRIU team.
criu 3.17.1 11/20/2024 COMPEL(1)
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