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.TH INIT_MODULE 2 2017-09-15 "Linux" "Linux Programmer's Manual"

.SH NAME

init_module, finit_module \- load a kernel module

.SH SYNOPSIS

.nf

.BI "int init_module(void *" module_image ", unsigned long " len ,

.BI "                const char *" param_values );

.PP

.BI "int finit_module(int " fd ", const char *" param_values ,

.BI "                 int " flags );

.fi

.PP

.IR Note :

glibc provides no header file declaration of

.BR init_module ()

and no wrapper function for

.BR finit_module ();

see NOTES.

.SH DESCRIPTION

.BR init_module ()

loads an ELF image into kernel space,

performs any necessary symbol relocations,

initializes module parameters to values provided by the caller,

and then runs the module's

.I init

function.

This system call requires privilege.

.PP

The

.I module_image

argument points to a buffer containing the binary image

to be loaded;

.I len

specifies the size of that buffer.

The module image should be a valid ELF image, built for the running kernel.

.PP

The

.I param_values

argument is a string containing space-delimited specifications of the

values for module parameters (defined inside the module using

.BR module_param ()

and

.BR module_param_array ()).

The kernel parses this string and initializes the specified

parameters.

Each of the parameter specifications has the form:

.PP

.RI "        " name [\c

.BI = value\c

.RB [ ,\c

.IR value ...]]

.PP

The parameter

.I name

is one of those defined within the module using

.IR module_param ()

(see the Linux kernel source file

.IR include/linux/moduleparam.h ).

The parameter

.I value

is optional in the case of

.I bool

and

.I invbool

parameters.

Values for array parameters are specified as a comma-separated list.

.SS finit_module()

The

.BR finit_module ()

.\" commit 34e1169d996ab148490c01b65b4ee371cf8ffba2

.\" https://lwn.net/Articles/519010/

system call is like

.BR init_module (),

but reads the module to be loaded from the file descriptor

.IR fd .

It is useful when the authenticity of a kernel module

can be determined from its location in the filesystem;

in cases where that is possible,

the overhead of using cryptographically signed modules to

determine the authenticity of a module can be avoided.

The

.I param_values

argument is as for

.BR init_module ().

.PP

The

.I flags

argument modifies the operation of

.BR finit_module ().

It is a bit mask value created by ORing

together zero or more of the following flags:

.\" commit 2f3238aebedb243804f58d62d57244edec4149b2

.TP

.B MODULE_INIT_IGNORE_MODVERSIONS

Ignore symbol version hashes.

.TP

.B MODULE_INIT_IGNORE_VERMAGIC

Ignore kernel version magic.

.PP

There are some safety checks built into a module to ensure that

it matches the kernel against which it is loaded.

.\" http://www.tldp.org/HOWTO/Module-HOWTO/basekerncompat.html

.\" is dated, but informative

These checks are recorded when the module is built and

verified when the module is loaded.

First, the module records a "vermagic" string containing

the kernel version number and prominent features (such as the CPU type).

Second, if the module was built with the

.B CONFIG_MODVERSIONS

configuration option enabled,

a version hash is recorded for each symbol the module uses.

This hash is based on the types of the arguments and return value

for the function named by the symbol.

In this case, the kernel version number within the

"vermagic" string is ignored,

as the symbol version hashes are assumed to be sufficiently reliable.

.PP

Using the

.B MODULE_INIT_IGNORE_VERMAGIC

flag indicates that the "vermagic" string is to be ignored, and the

.B MODULE_INIT_IGNORE_MODVERSIONS

flag indicates that the symbol version hashes are to be ignored.

If the kernel is built to permit forced loading (i.e., configured with

.BR CONFIG_MODULE_FORCE_LOAD ),

then loading continues, otherwise it fails with the error

.B ENOEXEC

as expected for malformed modules.

.SH RETURN VALUE

On success, these system calls return 0.

On error, \-1 is returned and

.I errno

is set appropriately.

.SH ERRORS

.TP

.BR EBADMSG " (since Linux 3.7)"

Module signature is misformatted.

.TP

.B EBUSY

Timeout while trying to resolve a symbol reference by this module.

.TP

.B EFAULT

An address argument referred to a location that

is outside the process's accessible address space.

.TP

.BR ENOKEY " (since Linux 3.7)"

.\" commit 48ba2462ace6072741fd8d0058207d630ce93bf1

.\" commit 1d0059f3a468825b5fc5405c636a2f6e02707ffa

.\" commit 106a4ee258d14818467829bf0e12aeae14c16cd7

Module signature is invalid or

the kernel does not have a key for this module.

This error is returned only if the kernel was configured with

.BR CONFIG_MODULE_SIG_FORCE ;

if the kernel was not configured with this option,

then an invalid or unsigned module simply taints the kernel.

.TP

.B ENOMEM

Out of memory.

.TP

.B EPERM

The caller was not privileged

(did not have the

.B CAP_SYS_MODULE

capability),

or module loading is disabled

(see

.IR /proc/sys/kernel/modules_disabled

in

.BR proc (5)).

.PP

The following errors may additionally occur for

.BR init_module ():

.TP

.B EEXIST

A module with this name is already loaded.

.TP

.B EINVAL

.I param_values

is invalid, or some part of the ELF image in

.IR module_image

contains inconsistencies.

.\" .TP

.\" .BR EINVAL " (Linux 2.4 and earlier)"

.\" Some

.\" .I image

.\" slot is filled in incorrectly,

.\" .I image\->name

.\" does not correspond to the original module name, some

.\" .I image\->deps

.\" entry does not correspond to a loaded module,

.\" or some other similar inconsistency.

.TP

.B ENOEXEC

The binary image supplied in

.I module_image

is not an ELF image,

or is an ELF image that is invalid or for a different architecture.

.PP

The following errors may additionally occur for

.BR finit_module ():

.TP

.B EBADF

The file referred to by

.I fd

is not opened for reading.

.TP

.B EFBIG

The file referred to by

.I fd

is too large.

.TP

.B EINVAL

.I flags

is invalid.

.TP

.B ENOEXEC

.I fd

does not refer to an open file.

.PP

In addition to the above errors, if the module's

.I init

function is executed and returns an error, then

.BR init_module ()

or

.BR finit_module ()

fails and

.I errno

is set to the value returned by the

.I init

function.

.SH VERSIONS

.BR finit_module ()

is available since Linux 3.8.

.SH CONFORMING TO

.BR init_module ()

and

.BR finit_module ()

are Linux-specific.

.SH NOTES

The

.BR init_module ()

system call is not supported by glibc.

No declaration is provided in glibc headers, but, through a quirk of history,

glibc versions before 2.23 did export an ABI for this system call.

Therefore, in order to employ this system call,

it is (before glibc 2.23) sufficient to

manually declare the interface in your code;

alternatively, you can invoke the system call using

.BR syscall (2).

.PP

Glibc does not provide a wrapper for

.BR finit_module ();

call it using

.BR syscall (2).

.PP

Information about currently loaded modules can be found in

.IR /proc/modules

and in the file trees under the per-module subdirectories under

.IR /sys/module .

.PP

See the Linux kernel source file

.I include/linux/module.h

for some useful background information.

.SS Linux 2.4 and earlier

.PP

In Linux 2.4 and earlier, the

.BR init_module ()

system call was rather different:

.PP

.B "    #include <linux/module.h>"

.PP

.BI "    int init_module(const char *" name ", struct module *" image );

.PP

(User-space applications can detect which version of

.BR init_module ()

is available by calling

.BR query_module ();

the latter call fails with the error

.BR ENOSYS

on Linux 2.6 and later.)

.PP

The older version of the system call

loads the relocated module image pointed to by

.I image

into kernel space and runs the module's

.I init

function.

The caller is responsible for providing the relocated image (since

Linux 2.6, the

.BR init_module ()

system call does the relocation).

.PP

The module image begins with a module structure and is followed by

code and data as appropriate.

Since Linux 2.2, the module structure is defined as follows:

.PP

.in +4n

.EX

struct module {

    unsigned long         size_of_struct;

    struct module        *next;

    const char           *name;

    unsigned long         size;

    long                  usecount;

    unsigned long         flags;

    unsigned int          nsyms;

    unsigned int          ndeps;

    struct module_symbol *syms;

    struct module_ref    *deps;

    struct module_ref    *refs;

    int                 (*init)(void);

    void                (*cleanup)(void);

    const struct exception_table_entry *ex_table_start;

    const struct exception_table_entry *ex_table_end;

#ifdef __alpha__

    unsigned long gp;

#endif

};

.EE

.in

.PP

All of the pointer fields, with the exception of

.I next

and

.IR refs ,

are expected to point within the module body and be

initialized as appropriate for kernel space, that is, relocated with

the rest of the module.

.SH SEE ALSO

.BR create_module (2),

.BR delete_module (2),

.BR query_module (2),

.BR lsmod (8),

.BR modprobe (8)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.