1init_module(2)                System Calls Manual               init_module(2)
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NAME

6       init_module, finit_module - load a kernel module
7

LIBRARY

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <linux/module.h>    /* Definition of MODULE_* constants */
13       #include <sys/syscall.h>     /* Definition of SYS_* constants */
14       #include <unistd.h>
15
16       int syscall(SYS_init_module, void module_image[.len], unsigned long len,
17                   const char *param_values);
18       int syscall(SYS_finit_module, int fd,
19                   const char *param_values, int flags);
20
21       Note:  glibc provides no wrappers for these system calls, necessitating
22       the use of syscall(2).
23

DESCRIPTION

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

87       On success, these system calls return 0.  On error, -1 is returned  and
88       errno is set to indicate the error.
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ERRORS

91       EBADMSG (since Linux 3.7)
92              Module signature is misformatted.
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94       EBUSY  Timeout  while trying to resolve a symbol reference by this mod‐
95              ule.
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97       EFAULT An address argument referred to a location that is  outside  the
98              process's accessible address space.
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100       ENOKEY (since Linux 3.7)
101              Module  signature  is  invalid or the kernel does not have a key
102              for this module.  This error is returned only if the kernel  was
103              configured  with  CONFIG_MODULE_SIG_FORCE; if the kernel was not
104              configured with this option, then an invalid or unsigned  module
105              simply taints the kernel.
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107       ENOMEM Out of memory.
108
109       EPERM  The  caller  was not privileged (did not have the CAP_SYS_MODULE
110              capability), or module loading is disabled  (see  /proc/sys/ker‐
111              nel/modules_disabled in proc(5)).
112
113       The following errors may additionally occur for init_module():
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115       EEXIST A module with this name is already loaded.
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117       EINVAL param_values  is  invalid, or some part of the ELF image in mod‐
118              ule_image contains inconsistencies.
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120       ENOEXEC
121              The binary image supplied in module_image is not an  ELF  image,
122              or  is an ELF image that is invalid or for a different architec‐
123              ture.
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125       The following errors may additionally occur for finit_module():
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127       EBADF  The file referred to by fd is not opened for reading.
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129       EFBIG  The file referred to by fd is too large.
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131       EINVAL flags is invalid.
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133       ENOEXEC
134              fd does not refer to an open file.
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136       ETXTBSY (since Linux 4.7)
137              The file referred to by fd is opened for read-write.
138
139       In addition to the above errors, if the module's init function is  exe‐
140       cuted  and returns an error, then init_module() or finit_module() fails
141       and errno is set to the value returned by the init function.
142

STANDARDS

144       Linux.
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HISTORY

147       finit_module()
148              Linux 3.8.
149
150       The init_module() system call is not supported by glibc.   No  declara‐
151       tion  is  provided  in  glibc headers, but, through a quirk of history,
152       glibc versions before glibc 2.23 did export  an  ABI  for  this  system
153       call.   Therefore,  in  order to employ this system call, it is (before
154       glibc 2.23) sufficient to manually declare the interface in your  code;
155       alternatively, you can invoke the system call using syscall(2).
156
157   Linux 2.4 and earlier
158       In Linux 2.4 and earlier, the init_module() system call was rather dif‐
159       ferent:
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161           #include <linux/module.h>
162
163           int init_module(const char *name, struct module *image);
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165       (User-space applications can detect which version of  init_module()  is
166       available by calling query_module(); the latter call fails with the er‐
167       ror ENOSYS on Linux 2.6 and later.)
168
169       The older version of the system call loads the relocated  module  image
170       pointed  to by image into kernel space and runs the module's init func‐
171       tion.  The caller is responsible  for  providing  the  relocated  image
172       (since Linux 2.6, the init_module() system call does the relocation).
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174       The module image begins with a module structure and is followed by code
175       and data as appropriate.  Since Linux 2.2, the module structure is  de‐
176       fined as follows:
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178           struct module {
179               unsigned long         size_of_struct;
180               struct module        *next;
181               const char           *name;
182               unsigned long         size;
183               long                  usecount;
184               unsigned long         flags;
185               unsigned int          nsyms;
186               unsigned int          ndeps;
187               struct module_symbol *syms;
188               struct module_ref    *deps;
189               struct module_ref    *refs;
190               int                 (*init)(void);
191               void                (*cleanup)(void);
192               const struct exception_table_entry *ex_table_start;
193               const struct exception_table_entry *ex_table_end;
194           #ifdef __alpha__
195               unsigned long gp;
196           #endif
197           };
198
199       All of the pointer fields, with the exception of next and refs, are ex‐
200       pected to point within the module body and be initialized as  appropri‐
201       ate for kernel space, that is, relocated with the rest of the module.
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NOTES

204       Information  about  currently loaded modules can be found in /proc/mod‐
205       ules and in the file trees under the  per-module  subdirectories  under
206       /sys/module.
207
208       See the Linux kernel source file include/linux/module.h for some useful
209       background information.
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SEE ALSO

212       create_module(2),  delete_module(2),  query_module(2),  lsmod(8),  mod‐
213       probe(8)
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217Linux man-pages 6.05              2023-03-30                    init_module(2)
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