Section: CRIU Manual (1)
compel - Execute parasitic code within another process.
compel hgen [option ...]
compel plugins [PLUGIN_NAME ...]
compel [--compat] includes | cflags | ldflags
compel [--compat] [--static] libs
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.
create a header from the .po file, which is the parasite binary.
prints the plugins available.
prints the ldflags available to compel during linking of parasite code.
prints the compel cflags to be used during compilation of parasitic code.
prints list of standard include directories.
prints list of static or dynamic libraries that compel can link with.
-f, --file FILE
Path to the binary file,
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.
Prints usage and exits.
Prints version number of compel.
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()
The parasitic code is compiled and converted to a header using compel, and included here.
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 ...);
int compel_infect(ctl, nr_thread, size_of_args_area);
cure the victim:
//ctl pointer is freed by this call
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.
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.
The CRIU team.