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fea681da | 1 | .\" Copyright (C) 1998 Andries Brouwer (aeb@cwi.nl) |
73d3ac53 | 2 | .\" and Copyright (C) 2002, 2006, 2008, 2012, 2013 Michael Kerrisk <mtk.manpages@gmail.com> |
af5f9508 | 3 | .\" and Copyright Guillem Jover <guillem@hadrons.org> |
3cd5e983 | 4 | .\" and Copyright (C) 2014 Dave Hansen / Intel |
fea681da | 5 | .\" |
93015253 | 6 | .\" %%%LICENSE_START(VERBATIM) |
fea681da MK |
7 | .\" Permission is granted to make and distribute verbatim copies of this |
8 | .\" manual provided the copyright notice and this permission notice are | |
9 | .\" preserved on all copies. | |
10 | .\" | |
11 | .\" Permission is granted to copy and distribute modified versions of this | |
12 | .\" manual under the conditions for verbatim copying, provided that the | |
13 | .\" entire resulting derived work is distributed under the terms of a | |
14 | .\" permission notice identical to this one. | |
c13182ef | 15 | .\" |
fea681da MK |
16 | .\" Since the Linux kernel and libraries are constantly changing, this |
17 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
18 | .\" responsibility for errors or omissions, or for damages resulting from | |
19 | .\" the use of the information contained herein. The author(s) may not | |
20 | .\" have taken the same level of care in the production of this manual, | |
21 | .\" which is licensed free of charge, as they might when working | |
22 | .\" professionally. | |
c13182ef | 23 | .\" |
fea681da MK |
24 | .\" Formatted or processed versions of this manual, if unaccompanied by |
25 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 26 | .\" %%%LICENSE_END |
fea681da MK |
27 | .\" |
28 | .\" Modified Thu Nov 11 04:19:42 MET 1999, aeb: added PR_GET_PDEATHSIG | |
29 | .\" Modified 27 Jun 02, Michael Kerrisk | |
c13182ef | 30 | .\" Added PR_SET_DUMPABLE, PR_GET_DUMPABLE, |
fea681da | 31 | .\" PR_SET_KEEPCAPS, PR_GET_KEEPCAPS |
e87fdd92 MK |
32 | .\" Modified 2006-08-30 Guillem Jover <guillem@hadrons.org> |
33 | .\" Updated Linux versions where the options where introduced. | |
34 | .\" Added PR_SET_TIMING, PR_GET_TIMING, PR_SET_NAME, PR_GET_NAME, | |
35 | .\" PR_SET_UNALIGN, PR_GET_UNALIGN, PR_SET_FPEMU, PR_GET_FPEMU, | |
36 | .\" PR_SET_FPEXC, PR_GET_FPEXC | |
8ab8b43f MK |
37 | .\" 2008-04-29 Serge Hallyn, Document PR_CAPBSET_READ and PR_CAPBSET_DROP |
38 | .\" 2008-06-13 Erik Bosman, <ejbosman@cs.vu.nl> | |
39 | .\" Document PR_GET_TSC and PR_SET_TSC. | |
40 | .\" 2008-06-15 mtk, Document PR_SET_SECCOMP, PR_GET_SECCOMP | |
bc02b3ea | 41 | .\" 2009-10-03 Andi Kleen, document PR_MCE_KILL |
06afe673 | 42 | .\" 2012-04 Cyrill Gorcunov, Document PR_SET_MM |
bc02b3ea MK |
43 | .\" 2012-04-25 Michael Kerrisk, Document PR_TASK_PERF_EVENTS_DISABLE and |
44 | .\" PR_TASK_PERF_EVENTS_ENABLE | |
34447828 | 45 | .\" 2012-09-20 Kees Cook, update PR_SET_SECCOMP for mode 2 |
f83fe154 | 46 | .\" 2012-09-20 Kees Cook, document PR_SET_NO_NEW_PRIVS, PR_GET_NO_NEW_PRIVS |
934487a0 MK |
47 | .\" 2012-10-25 Michael Kerrisk, Document PR_SET_TIMERSLACK and |
48 | .\" PR_GET_TIMERSLACK | |
491b2e75 | 49 | .\" 2013-01-10 Kees Cook, document PR_SET_PTRACER |
31cc8387 | 50 | .\" 2012-02-04 Michael Kerrisk, document PR_{SET,GET}_CHILD_SUBREAPER |
03979794 | 51 | .\" 2014-11-10 Dave Hansen, document PR_MPX_{EN,DIS}ABLE_MANAGEMENT |
fea681da | 52 | .\" |
e14baeeb | 53 | .\" |
3df541c0 | 54 | .TH PRCTL 2 2016-07-17 "Linux" "Linux Programmer's Manual" |
fea681da MK |
55 | .SH NAME |
56 | prctl \- operations on a process | |
57 | .SH SYNOPSIS | |
521bf584 | 58 | .nf |
fea681da MK |
59 | .B #include <sys/prctl.h> |
60 | .sp | |
521bf584 MK |
61 | .BI "int prctl(int " option ", unsigned long " arg2 ", unsigned long " arg3 , |
62 | .BI " unsigned long " arg4 ", unsigned long " arg5 ); | |
63 | .fi | |
fea681da | 64 | .SH DESCRIPTION |
e511ffb6 | 65 | .BR prctl () |
fea681da | 66 | is called with a first argument describing what to do |
1a329b56 | 67 | (with values defined in \fI<linux/prctl.h>\fP), and further |
c4bb193f | 68 | arguments with a significance depending on the first one. |
fea681da | 69 | The first argument can be: |
03547431 MK |
70 | .\" |
71 | .TP | |
72 | .BR PR_CAP_AMBIENT " (since Linux 4.3)" | |
73 | .\" commit 58319057b7847667f0c9585b9de0e8932b0fdb08 | |
74 | Reads or changes the ambient capability set, according to the value of | |
75 | .IR arg2 , | |
76 | which must be one of the following: | |
77 | .RS | |
78 | .\" | |
79 | .TP | |
80 | .B PR_CAP_AMBIENT_RAISE | |
81 | The capability specified in | |
82 | .I arg3 | |
83 | is added to the ambient set. | |
84 | The specified capability must already be present in | |
85 | both the permitted and the inheritable sets of the process. | |
86 | This operation is not permitted if the | |
87 | .B SECBIT_NO_CAP_AMBIENT_RAISE | |
88 | securebit is set. | |
89 | .TP | |
90 | .B PR_CAP_AMBIENT_LOWER | |
91 | The capability specified in | |
92 | .I arg3 | |
93 | is removed from the ambient set. | |
94 | .TP | |
95 | .B PR_CAP_AMBIENT_IS_SET | |
96 | The | |
bf7bc8b8 | 97 | .BR prctl () |
03547431 MK |
98 | call returns 1 if the capability in |
99 | .I arg3 | |
100 | is in the ambient set and 0 if it is not. | |
101 | .TP | |
102 | .BR PR_CAP_AMBIENT_CLEAR_ALL | |
103 | All capabilities will be removed from the ambient set. | |
104 | This operation requires setting | |
105 | .I arg3 | |
106 | to zero. | |
107 | .RE | |
269e3b97 MK |
108 | .IP |
109 | In all of the above operations, | |
110 | .I arg4 | |
111 | and | |
112 | .I arg5 | |
113 | must be specified as 0. | |
fea681da | 114 | .TP |
2e781e20 | 115 | .BR PR_CAPBSET_READ " (since Linux 2.6.25)" |
8ab8b43f MK |
116 | Return (as the function result) 1 if the capability specified in |
117 | .I arg2 | |
118 | is in the calling thread's capability bounding set, | |
119 | or 0 if it is not. | |
120 | (The capability constants are defined in | |
121 | .IR <linux/capability.h> .) | |
122 | The capability bounding set dictates | |
123 | whether the process can receive the capability through a | |
2914a14d | 124 | file's permitted capability set on a subsequent call to |
8ab8b43f MK |
125 | .BR execve (2). |
126 | ||
127 | If the capability specified in | |
128 | .I arg2 | |
129 | is not valid, then the call fails with the error | |
130 | .BR EINVAL . | |
131 | .TP | |
132 | .BR PR_CAPBSET_DROP " (since Linux 2.6.25)" | |
133 | If the calling thread has the | |
134 | .B CAP_SETPCAP | |
af53fcb5 | 135 | capability within its user namespace, then drop the capability specified by |
8ab8b43f MK |
136 | .I arg2 |
137 | from the calling thread's capability bounding set. | |
138 | Any children of the calling thread will inherit the newly | |
139 | reduced bounding set. | |
140 | ||
141 | The call fails with the error: | |
142 | .B EPERM | |
2914a14d | 143 | if the calling thread does not have the |
8ab8b43f MK |
144 | .BR CAP_SETPCAP ; |
145 | .BR EINVAL | |
146 | if | |
147 | .I arg2 | |
148 | does not represent a valid capability; or | |
149 | .BR EINVAL | |
150 | if file capabilities are not enabled in the kernel, | |
151 | in which case bounding sets are not supported. | |
73d3ac53 MK |
152 | .TP |
153 | .BR PR_SET_CHILD_SUBREAPER " (since Linux 3.4)" | |
154 | .\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b | |
155 | If | |
156 | .I arg2 | |
157 | is nonzero, | |
158 | set the "child subreaper" attribute of the calling process; | |
159 | if | |
160 | .I arg2 | |
161 | is zero, unset the attribute. | |
8b41eea4 | 162 | |
36127c0e | 163 | When a process is marked as a child subreaper, |
73d3ac53 MK |
164 | all of the children that it creates, and their descendants, |
165 | will be marked as having a subreaper. | |
166 | In effect, a subreaper fulfills the role of | |
167 | .BR init (1) | |
168 | for its descendant processes. | |
169 | Upon termination of a process | |
170 | that is orphaned (i.e., its immediate parent has already terminated) | |
171 | and marked as having a subreaper, | |
172 | the nearest still living ancestor subreaper | |
173 | will receive a | |
174 | .BR SIGCHLD | |
1a8e1c2f | 175 | signal and will be able to |
73d3ac53 MK |
176 | .BR wait (2) |
177 | on the process to discover its termination status. | |
73d3ac53 MK |
178 | .TP |
179 | .BR PR_GET_CHILD_SUBREAPER " (since Linux 3.4)" | |
180 | Return the "child subreaper" setting of the caller, | |
181 | in the location pointed to by | |
182 | .IR "(int\ *) arg2" . | |
8ab8b43f | 183 | .TP |
88989295 | 184 | .BR PR_SET_DUMPABLE " (since Linux 2.3.20)" |
2d7fc98d MK |
185 | Set the state of the "dumpable" flag, |
186 | which determines whether core dumps are produced for the calling process | |
187 | upon delivery of a signal whose default behavior is to produce a core dump. | |
4a3713a4 | 188 | |
88989295 | 189 | In kernels up to and including 2.6.12, |
8ab8b43f | 190 | .I arg2 |
8aad30d7 MK |
191 | must be either 0 |
192 | .RB ( SUID_DUMP_DISABLE , | |
193 | process is not dumpable) or 1 | |
194 | .RB ( SUID_DUMP_USER , | |
195 | process is dumpable). | |
0de51ed1 MK |
196 | Between kernels 2.6.13 and 2.6.17, |
197 | .\" commit abf75a5033d4da7b8a7e92321d74021d1fcfb502 | |
198 | the value 2 was also permitted, | |
88989295 MK |
199 | which caused any binary which normally would not be dumped |
200 | to be dumped readable by root only; | |
201 | for security reasons, this feature has been removed. | |
202 | .\" See http://marc.theaimsgroup.com/?l=linux-kernel&m=115270289030630&w=2 | |
203 | .\" Subject: Fix prctl privilege escalation (CVE-2006-2451) | |
204 | .\" From: Marcel Holtmann <marcel () holtmann ! org> | |
205 | .\" Date: 2006-07-12 11:12:00 | |
206 | (See also the description of | |
2d7fc98d | 207 | .I /proc/sys/fs/\:suid_dumpable |
88989295 MK |
208 | in |
209 | .BR proc (5).) | |
4a3713a4 | 210 | |
2d7fc98d MK |
211 | Normally, this flag is set to 1. |
212 | However, it is reset to the current value contained in the file | |
213 | .IR /proc/sys/fs/\:suid_dumpable | |
214 | (which by default has the value 0), | |
a644bc48 | 215 | in the following circumstances: |
2d7fc98d MK |
216 | .\" See kernel/cred.c::commit_creds() (Linux 3.18 sources) |
217 | .RS | |
218 | .IP * 3 | |
a644bc48 | 219 | The process's effective user or group ID is changed. |
2d7fc98d | 220 | .IP * |
a644bc48 | 221 | The process's filesystem user or group ID is changed (see |
2d7fc98d MK |
222 | .BR credentials (7)). |
223 | .IP * | |
a644bc48 | 224 | The process executes |
2d7fc98d | 225 | .RB ( execve (2)) |
a644bc48 | 226 | a set-user-ID or set-group-ID program, |
2d7fc98d | 227 | or a program that has capabilities (see |
a644bc48 | 228 | .BR capabilities (7)). |
5d28ea3e | 229 | .\" Also certain namespace operations; |
2d7fc98d MK |
230 | .RE |
231 | .IP | |
cadcf1b1 | 232 | Processes that are not dumpable can not be attached via |
6fdbc779 | 233 | .BR ptrace (2) |
982d8cf7 MK |
234 | .BR PTRACE_ATTACH ; |
235 | see | |
236 | .BR ptrace (2) | |
237 | for further details. | |
161946a2 MK |
238 | |
239 | If a process is not dumpable, | |
240 | the ownership of files in the process's | |
241 | .IR /proc/[pid] | |
242 | directory is affected as described in | |
243 | .BR proc (5). | |
64536a1b | 244 | .TP |
88989295 MK |
245 | .BR PR_GET_DUMPABLE " (since Linux 2.3.20)" |
246 | Return (as the function result) the current state of the calling | |
247 | process's dumpable flag. | |
248 | .\" Since Linux 2.6.13, the dumpable flag can have the value 2, | |
249 | .\" but in 2.6.13 PR_GET_DUMPABLE simply returns 1 if the dumpable | |
c7094399 | 250 | .\" flags has a nonzero value. This was fixed in 2.6.14. |
64536a1b | 251 | .TP |
8ab8b43f | 252 | .BR PR_SET_ENDIAN " (since Linux 2.6.18, PowerPC only)" |
c13182ef | 253 | Set the endian-ness of the calling process to the value given |
64536a1b | 254 | in \fIarg2\fP, which should be one of the following: |
8ab8b43f | 255 | .\" Respectively 0, 1, 2 |
64536a1b MK |
256 | .BR PR_ENDIAN_BIG , |
257 | .BR PR_ENDIAN_LITTLE , | |
258 | or | |
0daa9e92 | 259 | .B PR_ENDIAN_PPC_LITTLE |
64536a1b | 260 | (PowerPC pseudo little endian). |
e87fdd92 | 261 | .TP |
8ab8b43f MK |
262 | .BR PR_GET_ENDIAN " (since Linux 2.6.18, PowerPC only)" |
263 | Return the endian-ness of the calling process, | |
264 | in the location pointed to by | |
265 | .IR "(int\ *) arg2" . | |
64a53a67 ES |
266 | .TP |
267 | .BR PR_SET_FP_MODE " (since Linux 4.0, only on MIPS)" | |
89507305 MK |
268 | .\" commit 9791554b45a2acc28247f66a5fd5bbc212a6b8c8 |
269 | On the MIPS architecture, | |
270 | user-space code can be built using an ABI which permits linking | |
271 | with code that has more restrictive floating-point (FP) requirements. | |
272 | For example, user-space code may be built to target the O32 FPXX ABI | |
b3073df8 | 273 | and linked with code built for either one of the more restrictive |
89507305 | 274 | FP32 or FP64 ABIs. |
b3073df8 | 275 | When more restrictive code is linked in, |
89507305 MK |
276 | the overall requirement for the process is to use the more |
277 | restrictive floating-point mode. | |
278 | ||
07d6076e | 279 | Because the kernel has no means of knowing in advance |
89507305 | 280 | which mode the process should be executed in, |
07d6076e MK |
281 | and because these restrictions can |
282 | change over the lifetime of the process, the | |
283 | .B PR_SET_FP_MODE | |
284 | operation is provided to allow control of the floating-point mode | |
285 | from user space. | |
64a53a67 ES |
286 | |
287 | .\" https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking | |
288 | The | |
289 | .I (unsigned int) arg2 | |
89507305 | 290 | argument is a bit mask describing the floating-point mode used: |
64a53a67 ES |
291 | .RS |
292 | .TP | |
fb90e0c7 | 293 | .BR PR_FP_MODE_FR |
64a53a67 ES |
294 | When this bit is |
295 | .I unset | |
296 | (so called | |
297 | .BR FR=0 " or " FR0 | |
07d6076e | 298 | mode), the 32 floating-point registers are 32-bit wide, |
b3073df8 MK |
299 | and 64-bit registers are represented as pair of registers |
300 | (even- and odd- numbered, | |
89507305 MK |
301 | with the even-numbered register containing the lower 32 bits, |
302 | and the odd-numbered register containing the higher 32 bits). | |
303 | ||
64a53a67 ES |
304 | When this bit is |
305 | .I set | |
07d6076e MK |
306 | (on supported hardware), |
307 | the 32 floating-point registers are 64-bit wide (so called | |
64a53a67 | 308 | .BR FR=1 " or " FR1 |
89507305 | 309 | mode). |
b3073df8 | 310 | Note that modern MIPS implementations (MIPS R6 and newer) support |
64a53a67 ES |
311 | .B FR=1 |
312 | mode only. | |
313 | ||
07d6076e | 314 | |
89507305 | 315 | Applications that use the O32 FP32 ABI can operate only when this bit is |
64a53a67 ES |
316 | .I unset |
317 | .RB ( FR=0 ; | |
318 | or they can be used with FRE enabled, see below). | |
89507305 MK |
319 | Applications that use the O32 FP64 ABI |
320 | (and the O32 FP64A ABI, which exists to | |
321 | provide the ability to operate with existing FP32 code; see below) | |
322 | can operate only when this bit is | |
64a53a67 ES |
323 | .I set |
324 | .RB ( FR=1 ). | |
ffb0dafc | 325 | Applications that use the O32 FPXX ABI can operate with either |
07d6076e MK |
326 | .BR FR=0 |
327 | or | |
328 | .BR FR=1 . | |
64a53a67 | 329 | .TP |
fb90e0c7 | 330 | .BR PR_FP_MODE_FRE |
07d6076e | 331 | Enable emulation of 32-bit floating-point mode. |
b3073df8 | 332 | When this mode is enabled, |
07d6076e MK |
333 | it emulates 32-bit floating-point operations |
334 | by raising a reserved-instruction exception | |
b3073df8 | 335 | on every instruction that uses 32-bit formats and |
89507305 MK |
336 | the kernel then handles the instruction in software. |
337 | (The problem lies in the discrepancy of handling odd-numbered registers | |
338 | which are the high 32 bits of 64-bit registers with even numbers in | |
64a53a67 | 339 | .B FR=0 |
89507305 | 340 | mode and the lower 32-bit parts of odd-numbered 64-bit registers in |
64a53a67 | 341 | .B FR=1 |
89507305 MK |
342 | mode.) |
343 | Enabling this bit is necessary when code with the O32 FP32 ABI should operate | |
344 | with code with compatible the O32 FPXX or O32 FP64A ABIs (which require | |
64a53a67 | 345 | .B FR=1 |
b3073df8 MK |
346 | FPU mode) or when it is executed on newer hardware (MIPS R6 onwards) |
347 | which lacks | |
64a53a67 | 348 | .B FR=0 |
89507305 | 349 | mode support when a binary with the FP32 ABI is used. |
64a53a67 | 350 | .IP |
89507305 MK |
351 | Note that this mode makes sense only when the FPU is in 64-bit mode |
352 | .RB ( FR=1 ). | |
64a53a67 | 353 | .IP |
89507305 | 354 | Note that the use of emulation inherently has a significant performance hit |
b3073df8 | 355 | and should be avoided if possible. |
64a53a67 ES |
356 | .RE |
357 | .IP | |
07d6076e MK |
358 | In the N32/N64 ABI, 64-bit floating-point mode is always used, |
359 | so FPU emulation is not required and the FPU always operates in | |
64a53a67 ES |
360 | .B FR=1 |
361 | mode. | |
362 | .IP | |
07d6076e MK |
363 | This option is mainly intended for use by the dynamic linker |
364 | .RB ( ld.so (8)). | |
64a53a67 | 365 | .IP |
89507305 MK |
366 | The arguments |
367 | .IR arg3 , | |
368 | .IR arg4 , | |
369 | and | |
370 | .IR arg5 | |
64a53a67 ES |
371 | are ignored. |
372 | .TP | |
373 | .BR PR_GET_FP_MODE " (since Linux 4.0, only on MIPS)" | |
89507305 | 374 | Get the current floating-point mode (see the description of |
64a53a67 ES |
375 | .B PR_SET_FP_MODE |
376 | for details). | |
377 | ||
89507305 | 378 | On success, |
07d6076e | 379 | the call returns a bit mask which represents the current floating-point mode. |
89507305 MK |
380 | |
381 | The arguments | |
382 | .IR arg2 , | |
383 | .IR arg3 , | |
384 | .IR arg4 , | |
385 | and | |
386 | .IR arg5 | |
64a53a67 | 387 | are ignored. |
8ab8b43f | 388 | .TP |
8ab8b43f | 389 | .BR PR_SET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)" |
e87fdd92 | 390 | Set floating-point emulation control bits to \fIarg2\fP. |
7626d2ce MK |
391 | Pass |
392 | .B PR_FPEMU_NOPRINT | |
393 | to silently emulate floating-point operation accesses, or | |
394 | .B PR_FPEMU_SIGFPE | |
395 | to not emulate floating-point operations and send | |
8bd58774 MK |
396 | .B SIGFPE |
397 | instead. | |
e87fdd92 | 398 | .TP |
8ab8b43f MK |
399 | .BR PR_GET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)" |
400 | Return floating-point emulation control bits, | |
401 | in the location pointed to by | |
402 | .IR "(int\ *) arg2" . | |
e87fdd92 | 403 | .TP |
8ab8b43f | 404 | .BR PR_SET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)" |
1c44bd5b MK |
405 | Set floating-point exception mode to \fIarg2\fP. |
406 | Pass \fBPR_FP_EXC_SW_ENABLE\fP to use FPEXC for FP exception enables, | |
c45bd688 MK |
407 | \fBPR_FP_EXC_DIV\fP for floating-point divide by zero, |
408 | \fBPR_FP_EXC_OVF\fP for floating-point overflow, | |
409 | \fBPR_FP_EXC_UND\fP for floating-point underflow, | |
410 | \fBPR_FP_EXC_RES\fP for floating-point inexact result, | |
411 | \fBPR_FP_EXC_INV\fP for floating-point invalid operation, | |
e87fdd92 | 412 | \fBPR_FP_EXC_DISABLED\fP for FP exceptions disabled, |
b28f6e56 | 413 | \fBPR_FP_EXC_NONRECOV\fP for async nonrecoverable exception mode, |
e87fdd92 MK |
414 | \fBPR_FP_EXC_ASYNC\fP for async recoverable exception mode, |
415 | \fBPR_FP_EXC_PRECISE\fP for precise exception mode. | |
416 | .TP | |
8ab8b43f MK |
417 | .BR PR_GET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)" |
418 | Return floating-point exception mode, | |
419 | in the location pointed to by | |
420 | .IR "(int\ *) arg2" . | |
421 | .TP | |
88989295 MK |
422 | .BR PR_SET_KEEPCAPS " (since Linux 2.2.18)" |
423 | Set the state of the thread's "keep capabilities" flag, | |
88ee5c1c JW |
424 | which determines whether the thread's permitted |
425 | capability set is cleared when a change is made to the thread's user IDs | |
426 | such that the thread's real UID, effective UID, and saved set-user-ID | |
c7094399 | 427 | all become nonzero when at least one of them previously had the value 0. |
028cb080 MK |
428 | By default, the permitted capability set is cleared when such a change is made; |
429 | setting the "keep capabilities" flag prevents it from being cleared. | |
88989295 | 430 | .I arg2 |
028cb080 MK |
431 | must be either 0 (permitted capabilities are cleared) |
432 | or 1 (permitted capabilities are kept). | |
433 | (A thread's | |
434 | .I effective | |
435 | capability set is always cleared when such a credential change is made, | |
436 | regardless of the setting of the "keep capabilities" flag.) | |
437 | The "keep capabilities" value will be reset to 0 on subsequent calls to | |
88989295 MK |
438 | .BR execve (2). |
439 | .TP | |
440 | .BR PR_GET_KEEPCAPS " (since Linux 2.2.18)" | |
88ee5c1c | 441 | Return (as the function result) the current state of the calling thread's |
88989295 MK |
442 | "keep capabilities" flag. |
443 | .TP | |
03547431 MK |
444 | .BR PR_MCE_KILL " (since Linux 2.6.32)" |
445 | Set the machine check memory corruption kill policy for the current thread. | |
446 | If | |
447 | .I arg2 | |
448 | is | |
449 | .BR PR_MCE_KILL_CLEAR , | |
450 | clear the thread memory corruption kill policy and use the system-wide default. | |
451 | (The system-wide default is defined by | |
452 | .IR /proc/sys/vm/memory_failure_early_kill ; | |
453 | see | |
454 | .BR proc (5).) | |
455 | If | |
456 | .I arg2 | |
457 | is | |
458 | .BR PR_MCE_KILL_SET , | |
459 | use a thread-specific memory corruption kill policy. | |
460 | In this case, | |
461 | .I arg3 | |
462 | defines whether the policy is | |
463 | .I early kill | |
464 | .RB ( PR_MCE_KILL_EARLY ), | |
465 | .I late kill | |
466 | .RB ( PR_MCE_KILL_LATE ), | |
467 | or the system-wide default | |
468 | .RB ( PR_MCE_KILL_DEFAULT ). | |
469 | Early kill means that the thread receives a | |
470 | .B SIGBUS | |
471 | signal as soon as hardware memory corruption is detected inside | |
472 | its address space. | |
473 | In late kill mode, the process is killed only when it accesses a corrupted page. | |
474 | See | |
475 | .BR sigaction (2) | |
476 | for more information on the | |
477 | .BR SIGBUS | |
478 | signal. | |
479 | The policy is inherited by children. | |
480 | The remaining unused | |
481 | .BR prctl () | |
482 | arguments must be zero for future compatibility. | |
88989295 | 483 | .TP |
03547431 MK |
484 | .BR PR_MCE_KILL_GET " (since Linux 2.6.32)" |
485 | Return the current per-process machine check kill policy. | |
486 | All unused | |
487 | .BR prctl () | |
488 | arguments must be zero. | |
88989295 | 489 | .TP |
03547431 MK |
490 | .BR PR_SET_MM " (since Linux 3.3)" |
491 | .\" commit 028ee4be34a09a6d48bdf30ab991ae933a7bc036 | |
492 | Modify certain kernel memory map descriptor fields | |
493 | of the calling process. | |
494 | Usually these fields are set by the kernel and dynamic loader (see | |
495 | .BR ld.so (8) | |
496 | for more information) and a regular application should not use this feature. | |
497 | However, there are cases, such as self-modifying programs, | |
498 | where a program might find it useful to change its own memory map. | |
499 | This feature is available only if the kernel is built with the | |
500 | .BR CONFIG_CHECKPOINT_RESTORE | |
501 | option enabled. | |
502 | The calling process must have the | |
503 | .BR CAP_SYS_RESOURCE | |
504 | capability. | |
505 | The value in | |
506 | .I arg2 | |
507 | is one of the options below, while | |
508 | .I arg3 | |
509 | provides a new value for the option. | |
510 | .RS | |
511 | .TP | |
512 | .BR PR_SET_MM_START_CODE | |
513 | Set the address above which the program text can run. | |
514 | The corresponding memory area must be readable and executable, | |
515 | but not writable or sharable (see | |
516 | .BR mprotect (2) | |
0fcc276f | 517 | and |
03547431 MK |
518 | .BR mmap (2) |
519 | for more information). | |
f83fe154 | 520 | .TP |
03547431 MK |
521 | .BR PR_SET_MM_END_CODE |
522 | Set the address below which the program text can run. | |
523 | The corresponding memory area must be readable and executable, | |
524 | but not writable or sharable. | |
f83fe154 | 525 | .TP |
03547431 MK |
526 | .BR PR_SET_MM_START_DATA |
527 | Set the address above which initialized and | |
528 | uninitialized (bss) data are placed. | |
529 | The corresponding memory area must be readable and writable, | |
530 | but not executable or sharable. | |
88989295 | 531 | .TP |
03547431 MK |
532 | .B PR_SET_MM_END_DATA |
533 | Set the address below which initialized and | |
534 | uninitialized (bss) data are placed. | |
535 | The corresponding memory area must be readable and writable, | |
536 | but not executable or sharable. | |
88989295 | 537 | .TP |
03547431 MK |
538 | .BR PR_SET_MM_START_STACK |
539 | Set the start address of the stack. | |
540 | The corresponding memory area must be readable and writable. | |
491b2e75 | 541 | .TP |
03547431 MK |
542 | .BR PR_SET_MM_START_BRK |
543 | Set the address above which the program heap can be expanded with | |
544 | .BR brk (2) | |
545 | call. | |
546 | The address must be greater than the ending address of | |
547 | the current program data segment. | |
548 | In addition, the combined size of the resulting heap and | |
549 | the size of the data segment can't exceed the | |
550 | .BR RLIMIT_DATA | |
551 | resource limit (see | |
552 | .BR setrlimit (2)). | |
553 | .TP | |
554 | .BR PR_SET_MM_BRK | |
555 | Set the current | |
556 | .BR brk (2) | |
557 | value. | |
558 | The requirements for the address are the same as for the | |
559 | .BR PR_SET_MM_START_BRK | |
560 | option. | |
561 | .P | |
562 | The following options are available since Linux 3.5. | |
563 | .\" commit fe8c7f5cbf91124987106faa3bdf0c8b955c4cf7 | |
564 | .TP | |
565 | .BR PR_SET_MM_ARG_START | |
566 | Set the address above which the program command line is placed. | |
567 | .TP | |
568 | .BR PR_SET_MM_ARG_END | |
569 | Set the address below which the program command line is placed. | |
570 | .TP | |
571 | .BR PR_SET_MM_ENV_START | |
572 | Set the address above which the program environment is placed. | |
573 | .TP | |
574 | .BR PR_SET_MM_ENV_END | |
575 | Set the address below which the program environment is placed. | |
576 | .IP | |
577 | The address passed with | |
578 | .BR PR_SET_MM_ARG_START , | |
579 | .BR PR_SET_MM_ARG_END , | |
580 | .BR PR_SET_MM_ENV_START , | |
581 | and | |
582 | .BR PR_SET_MM_ENV_END | |
583 | should belong to a process stack area. | |
584 | Thus, the corresponding memory area must be readable, writable, and | |
585 | (depending on the kernel configuration) have the | |
586 | .BR MAP_GROWSDOWN | |
587 | attribute set (see | |
588 | .BR mmap (2)). | |
589 | .TP | |
590 | .BR PR_SET_MM_AUXV | |
591 | Set a new auxiliary vector. | |
592 | The | |
593 | .I arg3 | |
594 | argument should provide the address of the vector. | |
595 | The | |
596 | .I arg4 | |
597 | is the size of the vector. | |
598 | .TP | |
599 | .BR PR_SET_MM_EXE_FILE | |
600 | .\" commit b32dfe377102ce668775f8b6b1461f7ad428f8b6 | |
601 | Supersede the | |
602 | .IR /proc/pid/exe | |
603 | symbolic link with a new one pointing to a new executable file | |
604 | identified by the file descriptor provided in | |
605 | .I arg3 | |
606 | argument. | |
607 | The file descriptor should be obtained with a regular | |
608 | .BR open (2) | |
609 | call. | |
610 | .IP | |
611 | To change the symbolic link, one needs to unmap all existing | |
612 | executable memory areas, including those created by the kernel itself | |
613 | (for example the kernel usually creates at least one executable | |
614 | memory area for the ELF | |
615 | .IR \.text | |
616 | section). | |
617 | .IP | |
618 | The second limitation is that such transitions can be done only once | |
619 | in a process life time. | |
620 | Any further attempts will be rejected. | |
621 | This should help system administrators monitor unusual | |
622 | symbolic-link transitions over all processes running on a system. | |
623 | .RE | |
624 | .TP | |
625 | .BR PR_MPX_ENABLE_MANAGEMENT ", " PR_MPX_DISABLE_MANAGEMENT " (since Linux 3.19) " | |
626 | .\" commit fe3d197f84319d3bce379a9c0dc17b1f48ad358c | |
627 | .\" See also http://lwn.net/Articles/582712/ | |
628 | .\" See also https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler | |
629 | Enable or disable kernel management of Memory Protection eXtensions (MPX) | |
630 | bounds tables. | |
631 | The | |
632 | .IR arg2 , | |
633 | .IR arg3 , | |
634 | .IR arg4 , | |
635 | and | |
636 | .IR arg5 | |
637 | .\" commit e9d1b4f3c60997fe197bf0243cb4a41a44387a88 | |
638 | arguments must be zero. | |
639 | ||
640 | MPX is a hardware-assisted mechanism for performing bounds checking on | |
641 | pointers. | |
642 | It consists of a set of registers storing bounds information | |
643 | and a set of special instruction prefixes that tell the CPU on which | |
644 | instructions it should do bounds enforcement. | |
645 | There is a limited number of these registers and | |
646 | when there are more pointers than registers, | |
647 | their contents must be "spilled" into a set of tables. | |
648 | These tables are called "bounds tables" and the MPX | |
649 | .BR prctl () | |
650 | operations control | |
651 | whether the kernel manages their allocation and freeing. | |
652 | ||
653 | When management is enabled, the kernel will take over allocation | |
654 | and freeing of the bounds tables. | |
655 | It does this by trapping the #BR exceptions that result | |
656 | at first use of missing bounds tables and | |
657 | instead of delivering the exception to user space, | |
658 | it allocates the table and populates the bounds directory | |
659 | with the location of the new table. | |
660 | For freeing, the kernel checks to see if bounds tables are | |
661 | present for memory which is not allocated, and frees them if so. | |
662 | ||
663 | Before enabling MPX management using | |
664 | .BR PR_MPX_ENABLE_MANAGEMENT , | |
665 | the application must first have allocated a user-space buffer for | |
666 | the bounds directory and placed the location of that directory in the | |
667 | .I bndcfgu | |
668 | register. | |
669 | ||
670 | These calls will fail if the CPU or kernel does not support MPX. | |
671 | Kernel support for MPX is enabled via the | |
672 | .BR CONFIG_X86_INTEL_MPX | |
673 | configuration option. | |
674 | You can check whether the CPU supports MPX by looking for the 'mpx' | |
675 | CPUID bit, like with the following command: | |
676 | ||
677 | cat /proc/cpuinfo | grep ' mpx ' | |
678 | ||
679 | A thread may not switch in or out of long (64-bit) mode while MPX is | |
680 | enabled. | |
681 | ||
682 | All threads in a process are affected by these calls. | |
683 | ||
684 | The child of a | |
685 | .BR fork (2) | |
686 | inherits the state of MPX management. | |
687 | During | |
688 | .BR execve (2), | |
689 | MPX management is reset to a state as if | |
690 | .BR PR_MPX_DISABLE_MANAGEMENT | |
691 | had been called. | |
692 | ||
693 | For further information on Intel MPX, see the kernel source file | |
694 | .IR Documentation/x86/intel_mpx.txt . | |
695 | .TP | |
696 | .BR PR_SET_NAME " (since Linux 2.6.9)" | |
697 | Set the name of the calling thread, | |
698 | using the value in the location pointed to by | |
699 | .IR "(char\ *) arg2" . | |
700 | The name can be up to 16 bytes long, | |
701 | .\" TASK_COMM_LEN in include/linux/sched.h | |
702 | including the terminating null byte. | |
703 | (If the length of the string, including the terminating null byte, | |
704 | exceeds 16 bytes, the string is silently truncated.) | |
705 | This is the same attribute that can be set via | |
706 | .BR pthread_setname_np (3) | |
707 | and retrieved using | |
708 | .BR pthread_getname_np (3). | |
709 | The attribute is likewise accessible via | |
710 | .IR /proc/self/task/[tid]/comm , | |
711 | where | |
712 | .I tid | |
713 | is the name of the calling thread. | |
714 | .TP | |
715 | .BR PR_GET_NAME " (since Linux 2.6.11)" | |
716 | Return the name of the calling thread, | |
717 | in the buffer pointed to by | |
718 | .IR "(char\ *) arg2" . | |
719 | The buffer should allow space for up to 16 bytes; | |
720 | the returned string will be null-terminated. | |
721 | .TP | |
722 | .BR PR_SET_NO_NEW_PRIVS " (since Linux 3.5)" | |
723 | Set the calling process's | |
724 | .I no_new_privs | |
725 | bit to the value in | |
726 | .IR arg2 . | |
727 | With | |
728 | .I no_new_privs | |
729 | set to 1, | |
730 | .BR execve (2) | |
731 | promises not to grant privileges to do anything | |
732 | that could not have been done without the | |
733 | .BR execve (2) | |
734 | call (for example, | |
735 | rendering the set-user-ID and set-group-ID mode bits, | |
736 | and file capabilities non-functional). | |
737 | Once set, this bit cannot be unset. | |
738 | The setting of this bit is inherited by children created by | |
739 | .BR fork (2) | |
740 | and | |
741 | .BR clone (2), | |
742 | and preserved across | |
743 | .BR execve (2). | |
744 | ||
745 | For more information, see the kernel source file | |
746 | .IR Documentation/prctl/no_new_privs.txt . | |
747 | .TP | |
748 | .BR PR_GET_NO_NEW_PRIVS " (since Linux 3.5)" | |
749 | Return (as the function result) the value of the | |
750 | .I no_new_privs | |
751 | bit for the current process. | |
752 | A value of 0 indicates the regular | |
753 | .BR execve (2) | |
754 | behavior. | |
755 | A value of 1 indicates | |
756 | .BR execve (2) | |
757 | will operate in the privilege-restricting mode described above. | |
758 | .TP | |
759 | .BR PR_SET_PDEATHSIG " (since Linux 2.1.57)" | |
760 | Set the parent death signal | |
761 | of the calling process to \fIarg2\fP (either a signal value | |
762 | in the range 1..maxsig, or 0 to clear). | |
763 | This is the signal that the calling process will get when its | |
764 | parent dies. | |
765 | This value is cleared for the child of a | |
766 | .BR fork (2) | |
767 | and (since Linux 2.4.36 / 2.6.23) | |
768 | when executing a set-user-ID or set-group-ID binary, | |
769 | or a binary that has associated capabilities (see | |
770 | .BR capabilities (7)). | |
771 | This value is preserved across | |
772 | .BR execve (2). | |
773 | ||
774 | .IR Warning : | |
775 | .\" https://bugzilla.kernel.org/show_bug.cgi?id=43300 | |
776 | the "parent" in this case is considered to be the | |
777 | .I thread | |
778 | that created this process. | |
779 | In other words, the signal will be sent when that thread terminates | |
780 | (via, for example, | |
781 | .BR pthread_exit (3)), | |
782 | rather than after all of the threads in the parent process terminate. | |
783 | .TP | |
784 | .BR PR_GET_PDEATHSIG " (since Linux 2.3.15)" | |
785 | Return the current value of the parent process death signal, | |
786 | in the location pointed to by | |
787 | .IR "(int\ *) arg2" . | |
788 | .TP | |
789 | .BR PR_SET_PTRACER " (since Linux 3.4)" | |
790 | .\" commit 2d514487faf188938a4ee4fb3464eeecfbdcf8eb | |
791 | .\" commit bf06189e4d14641c0148bea16e9dd24943862215 | |
792 | This is meaningful only when the Yama LSM is enabled and in mode 1 | |
793 | ("restricted ptrace", visible via | |
794 | .IR /proc/sys/kernel/yama/ptrace_scope ). | |
795 | When a "ptracer process ID" is passed in \fIarg2\fP, | |
796 | the caller is declaring that the ptracer process can | |
797 | .BR ptrace (2) | |
798 | the calling process as if it were a direct process ancestor. | |
799 | Each | |
800 | .B PR_SET_PTRACER | |
801 | operation replaces the previous "ptracer process ID". | |
802 | Employing | |
803 | .B PR_SET_PTRACER | |
804 | with | |
805 | .I arg2 | |
806 | set to 0 clears the caller's "ptracer process ID". | |
807 | If | |
808 | .I arg2 | |
809 | is | |
810 | .BR PR_SET_PTRACER_ANY , | |
811 | the ptrace restrictions introduced by Yama are effectively disabled for the | |
812 | calling process. | |
813 | ||
814 | For further information, see the kernel source file | |
815 | .IR Documentation/security/Yama.txt . | |
816 | .TP | |
817 | .BR PR_SET_SECCOMP " (since Linux 2.6.23)" | |
818 | .\" See http://thread.gmane.org/gmane.linux.kernel/542632 | |
819 | .\" [PATCH 0 of 2] seccomp updates | |
820 | .\" andrea@cpushare.com | |
821 | Set the secure computing (seccomp) mode for the calling thread, to limit | |
822 | the available system calls. | |
823 | The more recent | |
824 | .BR seccomp (2) | |
825 | system call provides a superset of the functionality of | |
826 | .BR PR_SET_SECCOMP . | |
827 | ||
828 | The seccomp mode is selected via | |
829 | .IR arg2 . | |
830 | (The seccomp constants are defined in | |
831 | .IR <linux/seccomp.h> .) | |
34447828 KC |
832 | |
833 | With | |
8ab8b43f | 834 | .IR arg2 |
34447828 | 835 | set to |
b1248a9d | 836 | .BR SECCOMP_MODE_STRICT , |
8ab8b43f MK |
837 | the only system calls that the thread is permitted to make are |
838 | .BR read (2), | |
839 | .BR write (2), | |
85fbef74 MK |
840 | .BR _exit (2) |
841 | (but not | |
842 | .BR exit_group (2)), | |
fea681da | 843 | and |
8ab8b43f MK |
844 | .BR sigreturn (2). |
845 | Other system calls result in the delivery of a | |
846 | .BR SIGKILL | |
847 | signal. | |
34447828 | 848 | Strict secure computing mode is useful for number-crunching applications |
8ab8b43f MK |
849 | that may need to execute untrusted byte code, |
850 | perhaps obtained by reading from a pipe or socket. | |
33a0ccb2 | 851 | This operation is available only |
d6ef3d57 MK |
852 | if the kernel is configured with |
853 | .B CONFIG_SECCOMP | |
854 | enabled. | |
34447828 KC |
855 | |
856 | With | |
857 | .IR arg2 | |
858 | set to | |
b1248a9d | 859 | .BR SECCOMP_MODE_FILTER " (since Linux 3.5)," |
6239dfb2 MK |
860 | the system calls allowed are defined by a pointer |
861 | to a Berkeley Packet Filter passed in | |
862 | .IR arg3 . | |
863 | This argument is a pointer to | |
864 | .IR "struct sock_fprog" ; | |
865 | it can be designed to filter | |
d6ef3d57 | 866 | arbitrary system calls and system call arguments. |
33a0ccb2 | 867 | This mode is available only if the kernel is configured with |
d6ef3d57 MK |
868 | .B CONFIG_SECCOMP_FILTER |
869 | enabled. | |
34447828 | 870 | |
1733db35 MK |
871 | If |
872 | .BR SECCOMP_MODE_FILTER | |
873 | filters permit | |
874 | .BR fork (2), | |
990e3887 | 875 | then the seccomp mode is inherited by children created by |
1733db35 MK |
876 | .BR fork (2); |
877 | if | |
878 | .BR execve (2) | |
fa1d2749 | 879 | is permitted, then the seccomp mode is preserved across |
1733db35 MK |
880 | .BR execve (2). |
881 | If the filters permit | |
a26ec136 | 882 | .BR prctl () |
1733db35 MK |
883 | calls, then additional filters can be added; |
884 | they are run in order until the first non-allow result is seen. | |
885 | ||
6239dfb2 MK |
886 | For further information, see the kernel source file |
887 | .IR Documentation/prctl/seccomp_filter.txt . | |
8ab8b43f MK |
888 | .TP |
889 | .BR PR_GET_SECCOMP " (since Linux 2.6.23)" | |
5e91816c MK |
890 | Return (as the function result) |
891 | the secure computing mode of the calling thread. | |
34447828 KC |
892 | If the caller is not in secure computing mode, this operation returns 0; |
893 | if the caller is in strict secure computing mode, then the | |
8ab8b43f MK |
894 | .BR prctl () |
895 | call will cause a | |
896 | .B SIGKILL | |
897 | signal to be sent to the process. | |
d6ef3d57 | 898 | If the caller is in filter mode, and this system call is allowed by the |
8eeb062d MK |
899 | seccomp filters, it returns 2; otherwise, the process is killed with a |
900 | .BR SIGKILL | |
901 | signal. | |
33a0ccb2 | 902 | This operation is available only |
d6ef3d57 MK |
903 | if the kernel is configured with |
904 | .B CONFIG_SECCOMP | |
905 | enabled. | |
787843e7 MK |
906 | |
907 | Since Linux 3.8, the | |
908 | .IR Seccomp | |
909 | field of the | |
910 | .IR /proc/[pid]/status | |
911 | file provides a method of obtaining the same information, | |
912 | without the risk that the process is killed; see | |
913 | .BR proc (5). | |
88989295 MK |
914 | .TP |
915 | .BR PR_SET_SECUREBITS " (since Linux 2.6.26)" | |
916 | Set the "securebits" flags of the calling thread to the value supplied in | |
03547431 MK |
917 | .IR arg2 . |
918 | See | |
919 | .BR capabilities (7). | |
88989295 | 920 | .TP |
03547431 MK |
921 | .BR PR_GET_SECUREBITS " (since Linux 2.6.26)" |
922 | Return (as the function result) | |
923 | the "securebits" flags of the calling thread. | |
924 | See | |
925 | .BR capabilities (7). | |
926 | .TP | |
927 | .BR PR_SET_THP_DISABLE " (since Linux 3.15)" | |
928 | .\" commit a0715cc22601e8830ace98366c0c2bd8da52af52 | |
929 | Set the state of the "THP disable" flag for the calling thread. | |
930 | If | |
931 | .I arg2 | |
932 | has a nonzero value, the flag is set, otherwise it is cleared. | |
933 | Setting this flag provides a method | |
934 | for disabling transparent huge pages | |
935 | for jobs where the code cannot be modified, and using a malloc hook with | |
936 | .BR madvise (2) | |
937 | is not an option (i.e., statically allocated data). | |
938 | The setting of the "THP disable" flag is inherited by a child created via | |
939 | .BR fork (2) | |
940 | and is preserved across | |
941 | .BR execve (2). | |
942 | .\" | |
06afe673 MK |
943 | .TP |
944 | .BR PR_TASK_PERF_EVENTS_DISABLE " (since Linux 2.6.31)" | |
945 | Disable all performance counters attached to the calling process, | |
946 | regardless of whether the counters were created by | |
947 | this process or another process. | |
948 | Performance counters created by the calling process for other | |
949 | processes are unaffected. | |
66a9882e | 950 | For more information on performance counters, see the Linux kernel source file |
06afe673 MK |
951 | .IR tools/perf/design.txt . |
952 | .IP | |
03547431 MK |
953 | Originally called |
954 | .BR PR_TASK_PERF_COUNTERS_DISABLE ; | |
955 | .\" commit 1d1c7ddbfab358445a542715551301b7fc363e28 | |
956 | renamed (with same numerical value) | |
957 | in Linux 2.6.32. | |
958 | .\" | |
03979794 | 959 | .TP |
03547431 MK |
960 | .BR PR_TASK_PERF_EVENTS_ENABLE " (since Linux 2.6.31)" |
961 | The converse of | |
962 | .BR PR_TASK_PERF_EVENTS_DISABLE ; | |
963 | enable performance counters attached to the calling process. | |
964 | .IP | |
965 | Originally called | |
966 | .BR PR_TASK_PERF_COUNTERS_ENABLE ; | |
967 | .\" commit 1d1c7ddbfab358445a542715551301b7fc363e28 | |
968 | renamed | |
969 | .\" commit cdd6c482c9ff9c55475ee7392ec8f672eddb7be6 | |
970 | in Linux 2.6.32. | |
971 | .\" | |
972 | .TP | |
973 | .BR PR_GET_THP_DISABLE " (since Linux 3.15)" | |
974 | Return (via the function result) the current setting of the "THP disable" | |
975 | flag for the calling thread: | |
976 | either 1, if the flag is set, or 0, if it is not. | |
977 | .TP | |
978 | .BR PR_GET_TID_ADDRESS " (since Linux 3.5)" | |
979 | .\" commit 300f786b2683f8bb1ec0afb6e1851183a479c86d | |
980 | Retrieve the | |
981 | .I clear_child_tid | |
982 | address set by | |
983 | .BR set_tid_address (2) | |
984 | and the | |
985 | .BR clone (2) | |
986 | .B CLONE_CHILD_CLEARTID | |
987 | flag, in the location pointed to by | |
988 | .IR "(int\ **)\ arg2" . | |
989 | This feature is available only if the kernel is built with the | |
990 | .BR CONFIG_CHECKPOINT_RESTORE | |
991 | option enabled. | |
992 | .TP | |
993 | .BR PR_SET_TIMERSLACK " (since Linux 2.6.28)" | |
994 | .\" See https://lwn.net/Articles/369549/ | |
995 | .\" commit 6976675d94042fbd446231d1bd8b7de71a980ada | |
3780f8a5 MK |
996 | Each thread has two associated timer slack values: |
997 | a "default" value, and a "current" value. | |
998 | This operation sets the "current" timer slack value for the calling thread. | |
999 | If the nanosecond value supplied in | |
1000 | .IR arg2 | |
1001 | is greater than zero, then the "current" value is set to this value. | |
03547431 MK |
1002 | If |
1003 | .I arg2 | |
1004 | is less than or equal to zero, | |
1005 | .\" It seems that it's not possible to set the timer slack to zero; | |
1006 | .\" The minimum value is 1? Seems a little strange. | |
3780f8a5 MK |
1007 | the "current" timer slack is reset to the |
1008 | thread's "default" timer slack value. | |
1009 | ||
1010 | The "current" timer slack is used by the kernel to group timer expirations | |
03547431 MK |
1011 | for the calling thread that are close to one another; |
1012 | as a consequence, timer expirations for the thread may be | |
1013 | up to the specified number of nanoseconds late (but will never expire early). | |
1014 | Grouping timer expirations can help reduce system power consumption | |
1015 | by minimizing CPU wake-ups. | |
03979794 | 1016 | |
03547431 MK |
1017 | The timer expirations affected by timer slack are those set by |
1018 | .BR select (2), | |
1019 | .BR pselect (2), | |
1020 | .BR poll (2), | |
1021 | .BR ppoll (2), | |
1022 | .BR epoll_wait (2), | |
1023 | .BR epoll_pwait (2), | |
1024 | .BR clock_nanosleep (2), | |
1025 | .BR nanosleep (2), | |
1026 | and | |
1027 | .BR futex (2) | |
1028 | (and thus the library functions implemented via futexes, including | |
1029 | .\" List obtained by grepping for futex usage in glibc source | |
1030 | .BR pthread_cond_timedwait (3), | |
1031 | .BR pthread_mutex_timedlock (3), | |
1032 | .BR pthread_rwlock_timedrdlock (3), | |
1033 | .BR pthread_rwlock_timedwrlock (3), | |
1034 | and | |
1035 | .BR sem_timedwait (3)). | |
03979794 | 1036 | |
03547431 MK |
1037 | Timer slack is not applied to threads that are scheduled under |
1038 | a real-time scheduling policy (see | |
1039 | .BR sched_setscheduler (2)). | |
03979794 | 1040 | |
03547431 | 1041 | When a new thread is created, |
3780f8a5 | 1042 | the two timer slack values are made the same as the "current" value |
03547431 | 1043 | of the creating thread. |
3780f8a5 MK |
1044 | Thereafter, a thread can adjust its "current" timer slack value via |
1045 | .BR PR_SET_TIMERSLACK . | |
1046 | The "default" value can't be changed. | |
03547431 MK |
1047 | The timer slack values of |
1048 | .IR init | |
1049 | (PID 1), the ancestor of all processes, | |
1050 | are 50,000 nanoseconds (50 microseconds). | |
1051 | The timer slack values are preserved across | |
1052 | .BR execve (2). | |
c1f78aba MK |
1053 | |
1054 | Since Linux 4.6, the "current" timer slack value of any process | |
1055 | can be examined and changed via the file | |
1056 | .IR /proc/[pid]/timerslack_ns . | |
1057 | See | |
1058 | .BR proc (5). | |
e81a96ec | 1059 | .TP |
03547431 MK |
1060 | .BR PR_GET_TIMERSLACK " (since Linux 2.6.28)" |
1061 | Return (as the function result) | |
3780f8a5 | 1062 | the "current" timer slack value of the calling thread. |
4bf25b89 | 1063 | .TP |
03547431 MK |
1064 | .BR PR_SET_TIMING " (since Linux 2.6.0-test4)" |
1065 | Set whether to use (normal, traditional) statistical process timing or | |
1066 | accurate timestamp-based process timing, by passing | |
1067 | .B PR_TIMING_STATISTICAL | |
1068 | .\" 0 | |
1069 | or | |
1070 | .B PR_TIMING_TIMESTAMP | |
1071 | .\" 1 | |
1072 | to \fIarg2\fP. | |
1073 | .B PR_TIMING_TIMESTAMP | |
1074 | is not currently implemented | |
1075 | (attempting to set this mode will yield the error | |
1076 | .BR EINVAL ). | |
1077 | .\" PR_TIMING_TIMESTAMP doesn't do anything in 2.6.26-rc8, | |
1078 | .\" and looking at the patch history, it appears | |
1079 | .\" that it never did anything. | |
4bf25b89 | 1080 | .TP |
03547431 MK |
1081 | .BR PR_GET_TIMING " (since Linux 2.6.0-test4)" |
1082 | Return (as the function result) which process timing method is currently | |
1083 | in use. | |
4bf25b89 | 1084 | .TP |
03547431 MK |
1085 | .BR PR_SET_TSC " (since Linux 2.6.26, x86 only)" |
1086 | Set the state of the flag determining whether the timestamp counter | |
1087 | can be read by the process. | |
1088 | Pass | |
1089 | .B PR_TSC_ENABLE | |
1090 | to | |
1091 | .I arg2 | |
1092 | to allow it to be read, or | |
1093 | .B PR_TSC_SIGSEGV | |
1094 | to generate a | |
1095 | .B SIGSEGV | |
1096 | when the process tries to read the timestamp counter. | |
4bf25b89 | 1097 | .TP |
03547431 MK |
1098 | .BR PR_GET_TSC " (since Linux 2.6.26, x86 only)" |
1099 | Return the state of the flag determining whether the timestamp counter | |
1100 | can be read, | |
1101 | in the location pointed to by | |
1102 | .IR "(int\ *) arg2" . | |
1103 | .TP | |
1104 | .B PR_SET_UNALIGN | |
1105 | (Only on: ia64, since Linux 2.3.48; parisc, since Linux 2.6.15; | |
1106 | PowerPC, since Linux 2.6.18; Alpha, since Linux 2.6.22) | |
1107 | Set unaligned access control bits to \fIarg2\fP. | |
1108 | Pass | |
1109 | \fBPR_UNALIGN_NOPRINT\fP to silently fix up unaligned user accesses, | |
1110 | or \fBPR_UNALIGN_SIGBUS\fP to generate | |
1111 | .B SIGBUS | |
1112 | on unaligned user access. | |
1113 | .TP | |
1114 | .B PR_GET_UNALIGN | |
1115 | (see | |
1116 | .B PR_SET_UNALIGN | |
1117 | for information on versions and architectures) | |
1118 | Return unaligned access control bits, in the location pointed to by | |
1119 | .IR "(int\ *) arg2" . | |
47297adb | 1120 | .SH RETURN VALUE |
8ab8b43f MK |
1121 | On success, |
1122 | .BR PR_GET_DUMPABLE , | |
1123 | .BR PR_GET_KEEPCAPS , | |
f83fe154 | 1124 | .BR PR_GET_NO_NEW_PRIVS , |
5745985f | 1125 | .BR PR_GET_THP_DISABLE , |
8ab8b43f MK |
1126 | .BR PR_CAPBSET_READ , |
1127 | .BR PR_GET_TIMING , | |
c42db321 | 1128 | .BR PR_GET_TIMERSLACK , |
8ab8b43f | 1129 | .BR PR_GET_SECUREBITS , |
ed31c572 | 1130 | .BR PR_MCE_KILL_GET , |
0c3e75cb | 1131 | .BR PR_CAP_AMBIENT + PR_CAP_AMBIENT_IS_SET , |
8ab8b43f MK |
1132 | and (if it returns) |
1133 | .BR PR_GET_SECCOMP | |
2fda57bd | 1134 | return the nonnegative values described above. |
fea681da MK |
1135 | All other |
1136 | .I option | |
1137 | values return 0 on success. | |
1138 | On error, \-1 is returned, and | |
1139 | .I errno | |
1140 | is set appropriately. | |
1141 | .SH ERRORS | |
1142 | .TP | |
0478944d MK |
1143 | .B EACCES |
1144 | .I option | |
1145 | is | |
4ab9f1db MK |
1146 | .BR PR_SET_SECCOMP |
1147 | and | |
1148 | .I arg2 | |
1149 | is | |
1150 | .BR SECCOMP_MODE_FILTER , | |
1151 | but the process does not have the | |
1152 | .BR CAP_SYS_ADMIN | |
1153 | capability or has not set the | |
1154 | .IR no_new_privs | |
1155 | attribute (see the discussion of | |
1156 | .BR PR_SET_NO_NEW_PRIVS | |
1157 | above). | |
1158 | .TP | |
1159 | .B EACCES | |
1160 | .I option | |
1161 | is | |
0478944d MK |
1162 | .BR PR_SET_MM , |
1163 | and | |
1164 | .I arg3 | |
1165 | is | |
1166 | .BR PR_SET_MM_EXE_FILE , | |
1167 | the file is not executable. | |
1168 | .TP | |
1169 | .B EBADF | |
1170 | .I option | |
1171 | is | |
1172 | .BR PR_SET_MM , | |
1173 | .I arg3 | |
1174 | is | |
1175 | .BR PR_SET_MM_EXE_FILE , | |
1176 | and the file descriptor passed in | |
1177 | .I arg4 | |
1178 | is not valid. | |
1179 | .TP | |
1180 | .B EBUSY | |
1181 | .I option | |
1182 | is | |
1183 | .BR PR_SET_MM , | |
1184 | .I arg3 | |
1185 | is | |
1186 | .BR PR_SET_MM_EXE_FILE , | |
1187 | and this the second attempt to change the | |
1188 | .I /proc/pid/exe | |
1189 | symbolic link, which is prohibited. | |
1190 | .TP | |
8ab8b43f MK |
1191 | .B EFAULT |
1192 | .I arg2 | |
1193 | is an invalid address. | |
1194 | .TP | |
e35a0512 KC |
1195 | .B EFAULT |
1196 | .I option | |
1197 | is | |
1198 | .BR PR_SET_SECCOMP , | |
1199 | .I arg2 | |
1200 | is | |
1201 | .BR SECCOMP_MODE_FILTER , | |
1202 | the system was built with | |
64c626f7 | 1203 | .BR CONFIG_SECCOMP_FILTER , |
e35a0512 KC |
1204 | and |
1205 | .I arg3 | |
1206 | is an invalid address. | |
1207 | .TP | |
fea681da MK |
1208 | .B EINVAL |
1209 | The value of | |
1210 | .I option | |