init_module(2) — Linux manual page


init_module(2)             System Calls Manual            init_module(2)

NAME         top

       init_module, finit_module - load a kernel module

LIBRARY         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 module_image[.len], unsigned long len,
                   const char *param_values);
       int syscall(SYS_finit_module, int fd,
                   const char *param_values, int flags);

       Note: glibc provides no wrappers for these system calls,
       necessitating the use of syscall(2).

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 module_image argument points to a buffer containing the
       binary image to be loaded; len specifies the size of that buffer.
       The module image should be a valid ELF image, built for the
       running kernel.

       The param_values 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:


       The parameter name is one of those defined within the module
       using module_param() (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.

       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
       param_values 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:

              Ignore symbol version hashes.

              Ignore kernel version magic.

       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.

RETURN VALUE         top

       On success, these system calls return 0.  On error, -1 is
       returned and errno 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

       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/modules_disabled in proc(5)).

       The following errors may additionally occur for init_module():

       EEXIST A module with this name is already loaded.

       EINVAL param_values is invalid, or some part of the ELF image in
              module_image contains inconsistencies.

              The binary image supplied in module_image 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.

              fd does not refer to an open file.

       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 is set to the value returned by
       the init function.

STANDARDS         top


HISTORY         top

              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).

   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;
               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;

       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), delete_module(2), query_module(2), lsmod(8),

Linux man-pages (unreleased)     (date)                   init_module(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)