init_module(2)



INIT_MODULE(2)             Linux Programmer's Manual            INIT_MODULE(2)

NAME
       init_module, finit_module - load a kernel module

SYNOPSIS
       int init_module(void *module_image, unsigned long len,
                       const char *param_values);

       int finit_module(int fd, const char *param_values,
                        int flags);

       Note: glibc provides no header file declaration of init_module() and no
       wrapper function for finit_module(); see NOTES.

DESCRIPTION
       init_module() loads an ELF image into kernel space, performs any neces-
       sary  symbol  relocations, initializes module parameters to values pro-
       vided 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 speci-
       fications of the values for module parameters (defined inside the  mod-
       ule  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 mod-
       ule_param()  (see  the  Linux  kernel  source  file  include/linux/mod-
       uleparam.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 param_values argument is as  for  init_mod-
       ule().

       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.

       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  configura-
       tion  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 "ver-
       magic" 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  will  continue, otherwise it
       will fail with ENOEXEC as expected for malformed modules.

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

ERRORS
       EBADMSG (since Linux 3.7)
              Module signature is misformatted.

       EBUSY  Timeout  while trying to resolve a symbol reference by this mod-
              ule.

       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/ker-
              nel/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 mod-
              ule_image contains inconsistencies.

       ENOEXEC
              The binary image supplied in module_image is not an  ELF  image,
              or  is an ELF image that is invalid or for a different architec-
              ture.

       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.

       ENOEXEC
              fd does not refer to an open file.

       In addition to the above errors, if the module's init function is  exe-
       cuted  and returns an error, then init_module() or finit_module() fails
       and errno is set to the value returned by the init function.

VERSIONS
       finit_module() is available since Linux 3.8.

CONFORMING TO
       init_module() and finit_module() are Linux-specific.

NOTES
       The init_module() system call is not supported by glibc.   No  declara-
       tion  is  provided  in  glibc headers, but, through a quirk of history,
       glibc does export an ABI for this system call.  Therefore, in order  to
       employ  this  system  call,  it  is  sufficient to manually declare the
       interface in your code; alternatively, you can invoke the  system  call
       using syscall(2).

       Glibc  does  not  provide  a  wrapper for finit_module(); call it using
       syscall(2).

       Information about currently loaded modules can be found  in  /proc/mod-
       ules  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.

   Linux 2.4 and earlier
       In Linux 2.4 and earlier, the init_module() system call was rather dif-
       ferent:

           #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 func-
       tion.  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;
           #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  appro-
       priate  for  kernel space, that is, relocated with the rest of the mod-
       ule.

SEE ALSO
       create_module(2),  delete_module(2),  query_module(2),  lsmod(8),  mod-
       probe(8)

COLOPHON
       This  page  is  part of release 3.71 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux                             2014-05-10                    INIT_MODULE(2)

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