1INIT_MODULE(2)             Linux Programmer's Manual            INIT_MODULE(2)
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NAME

6       init_module, finit_module - load a kernel module
7

SYNOPSIS

9       #include <linux/module.h>    /* Definition of MODULE_* constants */
10       #include <sys/syscall.h>     /* Definition of SYS_* constants */
11       #include <unistd.h>
12
13       int syscall(SYS_init_module, void *module_image, unsigned long len,
14                   const char *param_values);
15       int syscall(SYS_finit_module, int fd, const char *param_values,
16                   int flags);
17
18       Note:  glibc provides no wrappers for these system calls, necessitating
19       the use of syscall(2).
20

DESCRIPTION

22       init_module() loads an ELF image into kernel space, performs any neces‐
23       sary  symbol  relocations, initializes module parameters to values pro‐
24       vided by the caller, and then runs the module's  init  function.   This
25       system call requires privilege.
26
27       The  module_image argument points to a buffer containing the binary im‐
28       age to be loaded; len specifies the size of that  buffer.   The  module
29       image should be a valid ELF image, built for the running kernel.
30
31       The param_values argument is a string containing space-delimited speci‐
32       fications of the values for module parameters (defined inside the  mod‐
33       ule  using module_param() and module_param_array()).  The kernel parses
34       this string and initializes the specified parameters.  Each of the  pa‐
35       rameter specifications has the form:
36
37               name[=value[,value...]]
38
39       The parameter name is one of those defined within the module using mod‐
40       ule_param()  (see  the  Linux  kernel  source  file  include/linux/mod‐
41       uleparam.h).   The  parameter value is optional in the case of bool and
42       invbool parameters.  Values for array parameters  are  specified  as  a
43       comma-separated list.
44
45   finit_module()
46       The  finit_module()  system  call  is like init_module(), but reads the
47       module to be loaded from the file descriptor fd.  It is useful when the
48       authenticity  of a kernel module can be determined from its location in
49       the filesystem; in cases where that is possible, the overhead of  using
50       cryptographically  signed  modules  to  determine the authenticity of a
51       module can be avoided.  The param_values argument is as  for  init_mod‐
52       ule().
53
54       The  flags  argument modifies the operation of finit_module().  It is a
55       bit mask value created by ORing together zero or more of the  following
56       flags:
57
58       MODULE_INIT_IGNORE_MODVERSIONS
59              Ignore symbol version hashes.
60
61       MODULE_INIT_IGNORE_VERMAGIC
62              Ignore kernel version magic.
63
64       There  are  some  safety  checks  built into a module to ensure that it
65       matches the kernel against  which  it  is  loaded.   These  checks  are
66       recorded  when  the  module  is  built  and verified when the module is
67       loaded.  First, the module records a "vermagic" string  containing  the
68       kernel  version  number  and prominent features (such as the CPU type).
69       Second, if the module was built with the CONFIG_MODVERSIONS  configura‐
70       tion  option  enabled,  a  version hash is recorded for each symbol the
71       module uses.  This hash is based on the types of the arguments and  re‐
72       turn  value  for  the  function named by the symbol.  In this case, the
73       kernel version number within the "vermagic" string is ignored,  as  the
74       symbol version hashes are assumed to be sufficiently reliable.
75
76       Using  the  MODULE_INIT_IGNORE_VERMAGIC  flag  indicates that the "ver‐
77       magic" string is to be ignored, and the  MODULE_INIT_IGNORE_MODVERSIONS
78       flag  indicates  that  the symbol version hashes are to be ignored.  If
79       the kernel is built to permit forced  loading  (i.e.,  configured  with
80       CONFIG_MODULE_FORCE_LOAD),  then  loading continues, otherwise it fails
81       with the error ENOEXEC as expected for malformed modules.
82

RETURN VALUE

84       On success, these system calls return 0.  On error, -1 is returned  and
85       errno is set to indicate the error.
86

ERRORS

88       EBADMSG (since Linux 3.7)
89              Module signature is misformatted.
90
91       EBUSY  Timeout  while trying to resolve a symbol reference by this mod‐
92              ule.
93
94       EFAULT An address argument referred to a location that is  outside  the
95              process's accessible address space.
96
97       ENOKEY (since Linux 3.7)
98              Module  signature  is  invalid or the kernel does not have a key
99              for this module.  This error is returned only if the kernel  was
100              configured  with  CONFIG_MODULE_SIG_FORCE; if the kernel was not
101              configured with this option, then an invalid or unsigned  module
102              simply taints the kernel.
103
104       ENOMEM Out of memory.
105
106       EPERM  The  caller  was not privileged (did not have the CAP_SYS_MODULE
107              capability), or module loading is disabled  (see  /proc/sys/ker‐
108              nel/modules_disabled in proc(5)).
109
110       The following errors may additionally occur for init_module():
111
112       EEXIST A module with this name is already loaded.
113
114       EINVAL param_values  is  invalid, or some part of the ELF image in mod‐
115              ule_image contains inconsistencies.
116
117       ENOEXEC
118              The binary image supplied in module_image is not an  ELF  image,
119              or  is an ELF image that is invalid or for a different architec‐
120              ture.
121
122       The following errors may additionally occur for finit_module():
123
124       EBADF  The file referred to by fd is not opened for reading.
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126       EFBIG  The file referred to by fd is too large.
127
128       EINVAL flags is invalid.
129
130       ENOEXEC
131              fd does not refer to an open file.
132
133       In addition to the above errors, if the module's init function is  exe‐
134       cuted  and returns an error, then init_module() or finit_module() fails
135       and errno is set to the value returned by the init function.
136

VERSIONS

138       finit_module() is available since Linux 3.8.
139

CONFORMING TO

141       init_module() and finit_module() are Linux-specific.
142

NOTES

144       The init_module() system call is not supported by glibc.   No  declara‐
145       tion  is  provided  in  glibc headers, but, through a quirk of history,
146       glibc versions before 2.23 did export an  ABI  for  this  system  call.
147       Therefore,  in  order  to  employ this system call, it is (before glibc
148       2.23) sufficient to manually declare the interface in your code; alter‐
149       natively, you can invoke the system call using syscall(2).
150
151       Information  about  currently loaded modules can be found in /proc/mod‐
152       ules and in the file trees under the  per-module  subdirectories  under
153       /sys/module.
154
155       See the Linux kernel source file include/linux/module.h for some useful
156       background information.
157
158   Linux 2.4 and earlier
159       In Linux 2.4 and earlier, the init_module() system call was rather dif‐
160       ferent:
161
162           #include <linux/module.h>
163
164           int init_module(const char *name, struct module *image);
165
166       (User-space  applications  can detect which version of init_module() is
167       available by calling query_module(); the latter call fails with the er‐
168       ror ENOSYS on Linux 2.6 and later.)
169
170       The  older  version of the system call loads the relocated module image
171       pointed to by image into kernel space and runs the module's init  func‐
172       tion.   The  caller  is  responsible  for providing the relocated image
173       (since Linux 2.6, the init_module() system call does the relocation).
174
175       The module image begins with a module structure and is followed by code
176       and  data as appropriate.  Since Linux 2.2, the module structure is de‐
177       fined as follows:
178
179           struct module {
180               unsigned long         size_of_struct;
181               struct module        *next;
182               const char           *name;
183               unsigned long         size;
184               long                  usecount;
185               unsigned long         flags;
186               unsigned int          nsyms;
187               unsigned int          ndeps;
188               struct module_symbol *syms;
189               struct module_ref    *deps;
190               struct module_ref    *refs;
191               int                 (*init)(void);
192               void                (*cleanup)(void);
193               const struct exception_table_entry *ex_table_start;
194               const struct exception_table_entry *ex_table_end;
195           #ifdef __alpha__
196               unsigned long gp;
197           #endif
198           };
199
200       All of the pointer fields, with the exception of next and refs, are ex‐
201       pected  to point within the module body and be initialized as appropri‐
202       ate for kernel space, that is, relocated with the rest of the module.
203

SEE ALSO

205       create_module(2),  delete_module(2),  query_module(2),  lsmod(8),  mod‐
206       probe(8)
207

COLOPHON

209       This  page  is  part of release 5.13 of the Linux man-pages project.  A
210       description of the project, information about reporting bugs,  and  the
211       latest     version     of     this    page,    can    be    found    at
212       https://www.kernel.org/doc/man-pages/.
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216Linux                             2021-03-22                    INIT_MODULE(2)
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