COMPEL

Section: CRIU Manual (1)
Updated: 07/27/2020
Page Index

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 resulting 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 compel_run_in_thread()

int parasite_daemon_cmd(int cmd, void *arg); // gets called by compel_rpc_call() and compel_rpc_call_sync()

void parasite_cleanup(void); //gets called on parasite unload by compel_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 perfomed 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 PREFIX_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 compel flags and linking it with the compel plugins.

AUTHOR

The CRIU team.