init_module(2) - Linux manual page (original) (raw)
initmodule(2) System Calls Manual initmodule(2)
NAME top
init_module, finit_module - load a kernel moduleLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <linux/module.h>** /* Definition of **MODULE_*** constants */
**#include <sys/syscall.h>** /* Definition of **SYS_*** constants */
**#include <unistd.h>**
**int syscall(SYS_init_module, void** _moduleimage_**[.**_size_**], unsigned long** _size_**,**
**const char ***_paramvalues_**);**
**int syscall(SYS_finit_module, int** _fd_**,**
**const char ***_paramvalues_**, int** _flags_**);**
_Note_: glibc provides no wrappers for these system calls,
necessitating the use of [syscall(2)](../man2/syscall.2.html).DESCRIPTION top
**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 _init_
function. This system call requires privilege.
The _moduleimage_ argument points to a buffer containing the binary
image to be loaded; _size_ specifies the size of that buffer. The
module image should be a valid ELF image, built for the running
kernel.
The _paramvalues_ argument is a string containing space-delimited
specifications of the values for module parameters (defined inside
the module using **module_param**() and **module_param_array**()). The
kernel parses this string and initializes the specified
parameters. Each of the parameter specifications has the form:
_name_[**=**_value_[**,**_value_...]]
The parameter _name_ is one of those defined within the module using
_moduleparam_() (see the Linux kernel source file
_include/linux/moduleparam.h_). The parameter _value_ is optional in
the case of _bool_ and _invbool_ parameters. Values for array
parameters are specified as a comma-separated list.finit_module() The finit_module() system call is like init_module(), but reads the module to be loaded from the file descriptor 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 paramvalues argument is as for init_module().
The _flags_ argument modifies the operation of **finit_module**(). It
is a bit mask value created by ORing together zero or more of the
following flags:
**MODULE_INIT_IGNORE_MODVERSIONS**
Ignore symbol version hashes.
**MODULE_INIT_IGNORE_VERMAGIC**
Ignore kernel version magic.
**MODULE_INIT_COMPRESSED_FILE** (since Linux 5.17)
Use in-kernel module decompression.
There are some safety checks built into a module to ensure that it
matches the kernel against which it is loaded. 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
**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.
Using the **MODULE_INIT_IGNORE_VERMAGIC** flag indicates that the
"vermagic" string is to be ignored, and the
**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
**CONFIG_MODULE_FORCE_LOAD**), then loading continues, otherwise it
fails with the error **ENOEXEC** as expected for malformed modules.
If the kernel was build with **CONFIG_MODULE_DECOMPRESS**, the in-
kernel decompression feature can be used. User-space code can
check if the kernel supports decompression by reading the
_/sys/module/compression_ attribute. If the kernel supports
decompression, the compressed file can directly be passed to
**finit_module**() using the **MODULE_INIT_COMPRESSED_FILE** flag. The
in-kernel module decompressor supports the following compression
algorithms:
• _gzip_ (since Linux 5.17)
• _xz_ (since Linux 5.17)
• _zstd_ (since Linux 6.2)
The kernel only implements a single decompression method. This is
selected during module generation accordingly to the compression
method chosen in the kernel configuration.RETURN VALUE top
On success, these system calls return 0. On error, -1 is returned
and _[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
**EBADMSG** (since Linux 3.7)
Module signature is misformatted.
**EBUSY** Timeout while trying to resolve a symbol reference by this
module.
**EFAULT** An address argument referred to a location that is outside
the process's accessible address space.
**ENOKEY** (since Linux 3.7)
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 **CONFIG_MODULE_SIG_FORCE**; if the
kernel was not configured with this option, then an invalid
or unsigned module simply taints the kernel.
**ENOMEM** Out of memory.
**EPERM** The caller was not privileged (did not have the
**CAP_SYS_MODULE** capability), or module loading is disabled
(see _/proc/sys/kernel/modulesdisabled_ in [proc(5)](../man5/proc.5.html)).
The following errors may additionally occur for **init_module**():
**EEXIST** A module with this name is already loaded.
**EINVAL** _paramvalues_ is invalid, or some part of the ELF image in
_moduleimage_ contains inconsistencies.
**ENOEXEC**
The binary image supplied in _moduleimage_ is not an ELF
image, or is an ELF image that is invalid or for a
different architecture.
The following errors may additionally occur for **finit_module**():
**EBADF** The file referred to by _fd_ is not opened for reading.
**EFBIG** The file referred to by _fd_ is too large.
**EINVAL** _flags_ is invalid.
**EINVAL** The decompressor sanity checks failed, while loading a
compressed module with flag **MODULE_INIT_COMPRESSED_FILE**
set.
**ENOEXEC**
_fd_ does not refer to an open file.
**EOPNOTSUPP** (since Linux 5.17)
The flag **MODULE_INIT_COMPRESSED_FILE** is set to load a
compressed module, and the kernel was built without
**CONFIG_MODULE_DECOMPRESS**.
**ETXTBSY** (since Linux 4.7)
The file referred to by _fd_ is opened for read-write.
In addition to the above errors, if the module's _init_ function is
executed and returns an error, then **init_module**() or
**finit_module**() fails and _[errno](../man3/errno.3.html)_ is set to the value returned by the
_init_ function.STANDARDS top
Linux.HISTORY top
**finit_module**()
Linux 3.8.
The **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 glibc 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 [syscall(2)](../man2/syscall.2.html).Linux 2.4 and earlier In Linux 2.4 and earlier, the init_module() system call was rather different:
**#include <linux/module.h>**
**int init_module(const char ***_name_**, struct module ***_image_**);**
(User-space applications can detect which version of **init_module**()
is available by calling **query_module**(); the latter call fails with
the error **ENOSYS** on Linux 2.6 and later.)
The older version of the system call loads the relocated module
image pointed to by _image_ into kernel space and runs the module's
_init_ function. The caller is responsible for providing the
relocated image (since Linux 2.6, the **init_module**() system call
does the relocation).
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:
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;
typeof(int (void)) *init;
typeof(void (void)) *cleanup;
const struct exception_table_entry *ex_table_start;
const struct exception_table_entry *ex_table_end;
#ifdef __alpha__
unsigned long gp;
#endif
};
All of the pointer fields, with the exception of _next_ and _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.NOTES top
Information about currently loaded modules can be found in
_/proc/modules_ and in the file trees under the per-module
subdirectories under _/sys/module_.
See the Linux kernel source file _include/linux/module.h_ for some
useful background information.SEE ALSO top
[create_module(2)](../man2/create%5Fmodule.2.html), [delete_module(2)](../man2/delete%5Fmodule.2.html), [query_module(2)](../man2/query%5Fmodule.2.html), [lsmod(8)](../man8/lsmod.8.html),
[modprobe(8)](../man8/modprobe.8.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2025-01-05 initmodule(2)
Pages that refer to this page:create_module(2), delete_module(2), get_kernel_syms(2), query_module(2), syscalls(2), unimplemented(2), systemd.exec(5), capabilities(7)