man2/prctl.2

   1 .\" Copyright (C) 1998 Andries Brouwer (aeb@cwi.nl)
   2 .\" and Copyright (C) 2002, 2006, 2008, 2012, 2013 Michael Kerrisk <mtk.manpages@gmail.com>
   3 .\" and Copyright Guillem Jover <guillem@hadrons.org>
   4 .\" and Copyright (C) 2014 Dave Hansen / Intel
   5 .\"
   6 .\" %%%LICENSE_START(VERBATIM)
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   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.
  15 .\"
  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  17 .\" manual page may be incorrect or out-of-date.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
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  24 .\" Formatted or processed versions of this manual, if unaccompanied by
  25 .\" the source, must acknowledge the copyright and authors of this work.
  26 .\" %%%LICENSE_END
  27 .\"
  28 .\" Modified Thu Nov 11 04:19:42 MET 1999, aeb: added PR_GET_PDEATHSIG
  29 .\" Modified 27 Jun 02, Michael Kerrisk
  30 .\"     Added PR_SET_DUMPABLE, PR_GET_DUMPABLE,
  31 .\"     PR_SET_KEEPCAPS, PR_GET_KEEPCAPS
  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
  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
  41 .\" 2009-10-03 Andi Kleen, document PR_MCE_KILL
  42 .\" 2012-04 Cyrill Gorcunov, Document PR_SET_MM
  43 .\" 2012-04-25 Michael Kerrisk, Document PR_TASK_PERF_EVENTS_DISABLE and
  44 .\"                             PR_TASK_PERF_EVENTS_ENABLE
  45 .\" 2012-09-20 Kees Cook, update PR_SET_SECCOMP for mode 2
  46 .\" 2012-09-20 Kees Cook, document PR_SET_NO_NEW_PRIVS, PR_GET_NO_NEW_PRIVS
  47 .\" 2012-10-25 Michael Kerrisk, Document PR_SET_TIMERSLACK and
  48 .\"                             PR_GET_TIMERSLACK
  49 .\" 2013-01-10 Kees Cook, document PR_SET_PTRACER
  50 .\" 2012-02-04 Michael Kerrisk, document PR_{SET,GET}_CHILD_SUBREAPER
  51 .\" 2014-11-10 Dave Hansen, document PR_MPX_{EN,DIS}ABLE_MANAGEMENT
  52 .\"
  53 .\"
  54 .TH PRCTL 2 2016-12-12 "Linux" "Linux Programmer's Manual"
  55 .SH NAME
  56 prctl \- operations on a process
  57 .SH SYNOPSIS
  58 .nf
  59 .B #include <sys/prctl.h>
  60 .sp
  61 .BI "int prctl(int " option ", unsigned long " arg2 ", unsigned long " arg3 ,
  62 .BI "          unsigned long " arg4 ", unsigned long " arg5 );
  63 .fi
  64 .SH DESCRIPTION
  65 .BR prctl ()
  66 is called with a first argument describing what to do
  67 (with values defined in \fI<linux/prctl.h>\fP), and further
  68 arguments with a significance depending on the first one.
  69 The first argument can be:
  70 .\"
  71 .TP
  72 .BR PR_CAP_AMBIENT " (since Linux 4.3)"
  73 .\" commit 58319057b7847667f0c9585b9de0e8932b0fdb08
  74 Reads or changes the ambient capability set of the calling thread,
  75 according to the value of
  76 .IR arg2 ,
  77 which must be one of the following:
  78 .RS
  79 .\"
  80 .TP
  81 .B PR_CAP_AMBIENT_RAISE
  82 The capability specified in
  83 .I arg3
  84 is added to the ambient set.
  85 The specified capability must already be present in
  86 both the permitted and the inheritable sets of the process.
  87 This operation is not permitted if the
  88 .B SECBIT_NO_CAP_AMBIENT_RAISE
  89 securebit is set.
  90 .TP
  91 .B PR_CAP_AMBIENT_LOWER
  92 The capability specified in
  93 .I arg3
  94 is removed from the ambient set.
  95 .TP
  96 .B PR_CAP_AMBIENT_IS_SET
  97 The
  98 .BR prctl ()
  99 call returns 1 if the capability in
 100 .I arg3
 101 is in the ambient set and 0 if it is not.
 102 .TP
 103 .BR PR_CAP_AMBIENT_CLEAR_ALL
 104 All capabilities will be removed from the ambient set.
 105 This operation requires setting
 106 .I arg3
 107 to zero.
 108 .RE
 109 .IP
 110 In all of the above operations,
 111 .I arg4
 112 and
 113 .I arg5
 114 must be specified as 0.
 115 .TP
 116 .BR PR_CAPBSET_READ " (since Linux 2.6.25)"
 117 Return (as the function result) 1 if the capability specified in
 118 .I arg2
 119 is in the calling thread's capability bounding set,
 120 or 0 if it is not.
 121 (The capability constants are defined in
 122 .IR <linux/capability.h> .)
 123 The capability bounding set dictates
 124 whether the process can receive the capability through a
 125 file's permitted capability set on a subsequent call to
 126 .BR execve (2).
 127
 128 If the capability specified in
 129 .I arg2
 130 is not valid, then the call fails with the error
 131 .BR EINVAL .
 132 .TP
 133 .BR PR_CAPBSET_DROP " (since Linux 2.6.25)"
 134 If the calling thread has the
 135 .B CAP_SETPCAP
 136 capability within its user namespace, then drop the capability specified by
 137 .I arg2
 138 from the calling thread's capability bounding set.
 139 Any children of the calling thread will inherit the newly
 140 reduced bounding set.
 141
 142 The call fails with the error:
 143 .B EPERM
 144 if the calling thread does not have the
 145 .BR CAP_SETPCAP ;
 146 .BR EINVAL
 147 if
 148 .I arg2
 149 does not represent a valid capability; or
 150 .BR EINVAL
 151 if file capabilities are not enabled in the kernel,
 152 in which case bounding sets are not supported.
 153 .TP
 154 .BR PR_SET_CHILD_SUBREAPER " (since Linux 3.4)"
 155 .\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b
 156 If
 157 .I arg2
 158 is nonzero,
 159 set the "child subreaper" attribute of the calling process;
 160 if
 161 .I arg2
 162 is zero, unset the attribute.
 163
 164 When a process is marked as a child subreaper,
 165 all of the children that it creates, and their descendants,
 166 will be marked as having a subreaper.
 167 In effect, a subreaper fulfills the role of
 168 .BR init (1)
 169 for its descendant processes.
 170 Upon termination of a process
 171 that is orphaned (i.e., its immediate parent has already terminated)
 172 and marked as having a subreaper,
 173 the nearest still living ancestor subreaper
 174 will receive a
 175 .BR SIGCHLD
 176 signal and will be able to
 177 .BR wait (2)
 178 on the process to discover its termination status.
 179
 180 The setting of this bit is not inherited by children created by
 181 .BR fork (2)
 182 and
 183 .BR clone (2).
 184 The setting is preserved across
 185 .BR execve (2).
 186 .TP
 187 .BR PR_GET_CHILD_SUBREAPER " (since Linux 3.4)"
 188 Return the "child subreaper" setting of the caller,
 189 in the location pointed to by
 190 .IR "(int\ *) arg2" .
 191 .TP
 192 .BR PR_SET_DUMPABLE " (since Linux 2.3.20)"
 193 Set the state of the "dumpable" flag,
 194 which determines whether core dumps are produced for the calling process
 195 upon delivery of a signal whose default behavior is to produce a core dump.
 196
 197 In kernels up to and including 2.6.12,
 198 .I arg2
 199 must be either 0
 200 .RB ( SUID_DUMP_DISABLE ,
 201 process is not dumpable) or 1
 202 .RB ( SUID_DUMP_USER ,
 203 process is dumpable).
 204 Between kernels 2.6.13 and 2.6.17,
 205 .\" commit abf75a5033d4da7b8a7e92321d74021d1fcfb502
 206 the value 2 was also permitted,
 207 which caused any binary which normally would not be dumped
 208 to be dumped readable by root only;
 209 for security reasons, this feature has been removed.
 210 .\" See http://marc.theaimsgroup.com/?l=linux-kernel&m=115270289030630&w=2
 211 .\" Subject:    Fix prctl privilege escalation (CVE-2006-2451)
 212 .\" From:       Marcel Holtmann <marcel () holtmann ! org>
 213 .\" Date:       2006-07-12 11:12:00
 214 (See also the description of
 215 .I /proc/sys/fs/\:suid_dumpable
 216 in
 217 .BR proc (5).)
 218
 219 Normally, this flag is set to 1.
 220 However, it is reset to the current value contained in the file
 221 .IR /proc/sys/fs/\:suid_dumpable
 222 (which by default has the value 0),
 223 in the following circumstances:
 224 .\" See kernel/cred.c::commit_creds() (Linux 3.18 sources)
 225 .RS
 226 .IP * 3
 227 The process's effective user or group ID is changed.
 228 .IP *
 229 The process's filesystem user or group ID is changed (see
 230 .BR credentials (7)).
 231 .IP *
 232 The process executes
 233 .RB ( execve (2))
 234 a set-user-ID or set-group-ID program, resulting in a change
 235 of either the effective user ID or the effective group ID.
 236 .IP *
 237 The process executes
 238 .RB ( execve (2))
 239 a program that has file capabilities (see
 240 .BR capabilities (7)),
 241 .\" See kernel/cred.c::commit_creds()
 242 but only if the permitted capabilities
 243 gained exceed those already permitted for the process.
 244 .\" Also certain namespace operations;
 245 .RE
 246 .IP
 247 Processes that are not dumpable can not be attached via
 248 .BR ptrace (2)
 249 .BR PTRACE_ATTACH ;
 250 see
 251 .BR ptrace (2)
 252 for further details.
 253
 254 If a process is not dumpable,
 255 the ownership of files in the process's
 256 .IR /proc/[pid]
 257 directory is affected as described in
 258 .BR proc (5).
 259 .TP
 260 .BR PR_GET_DUMPABLE " (since Linux 2.3.20)"
 261 Return (as the function result) the current state of the calling
 262 process's dumpable flag.
 263 .\" Since Linux 2.6.13, the dumpable flag can have the value 2,
 264 .\" but in 2.6.13 PR_GET_DUMPABLE simply returns 1 if the dumpable
 265 .\" flags has a nonzero value.  This was fixed in 2.6.14.
 266 .TP
 267 .BR PR_SET_ENDIAN " (since Linux 2.6.18, PowerPC only)"
 268 Set the endian-ness of the calling process to the value given
 269 in \fIarg2\fP, which should be one of the following:
 270 .\" Respectively 0, 1, 2
 271 .BR PR_ENDIAN_BIG ,
 272 .BR PR_ENDIAN_LITTLE ,
 273 or
 274 .B PR_ENDIAN_PPC_LITTLE
 275 (PowerPC pseudo little endian).
 276 .TP
 277 .BR PR_GET_ENDIAN " (since Linux 2.6.18, PowerPC only)"
 278 Return the endian-ness of the calling process,
 279 in the location pointed to by
 280 .IR "(int\ *) arg2" .
 281 .TP
 282 .BR PR_SET_FP_MODE " (since Linux 4.0, only on MIPS)"
 283 .\" commit 9791554b45a2acc28247f66a5fd5bbc212a6b8c8
 284 On the MIPS architecture,
 285 user-space code can be built using an ABI which permits linking
 286 with code that has more restrictive floating-point (FP) requirements.
 287 For example, user-space code may be built to target the O32 FPXX ABI
 288 and linked with code built for either one of the more restrictive
 289 FP32 or FP64 ABIs.
 290 When more restrictive code is linked in,
 291 the overall requirement for the process is to use the more
 292 restrictive floating-point mode.
 293
 294 Because the kernel has no means of knowing in advance
 295 which mode the process should be executed in,
 296 and because these restrictions can
 297 change over the lifetime of the process, the
 298 .B PR_SET_FP_MODE
 299 operation is provided to allow control of the floating-point mode
 300 from user space.
 301
 302 .\" https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking
 303 The
 304 .I (unsigned int) arg2
 305 argument is a bit mask describing the floating-point mode used:
 306 .RS
 307 .TP
 308 .BR PR_FP_MODE_FR
 309 When this bit is
 310 .I unset
 311 (so called
 312 .BR FR=0 " or " FR0
 313 mode), the 32 floating-point registers are 32 bits wide,
 314 and 64-bit registers are represented as a pair of registers
 315 (even- and odd- numbered,
 316 with the even-numbered register containing the lower 32 bits,
 317 and the odd-numbered register containing the higher 32 bits).
 318
 319 When this bit is
 320 .I set
 321 (on supported hardware),
 322 the 32 floating-point registers are 64 bits wide (so called
 323 .BR FR=1 " or " FR1
 324 mode).
 325 Note that modern MIPS implementations (MIPS R6 and newer) support
 326 .B FR=1
 327 mode only.
 328
 329
 330 Applications that use the O32 FP32 ABI can operate only when this bit is
 331 .I unset
 332 .RB ( FR=0 ;
 333 or they can be used with FRE enabled, see below).
 334 Applications that use the O32 FP64 ABI
 335 (and the O32 FP64A ABI, which exists to
 336 provide the ability to operate with existing FP32 code; see below)
 337 can operate only when this bit is
 338 .I set
 339 .RB ( FR=1 ).
 340 Applications that use the O32 FPXX ABI can operate with either
 341 .BR FR=0
 342 or
 343 .BR FR=1 .
 344 .TP
 345 .BR PR_FP_MODE_FRE
 346 Enable emulation of 32-bit floating-point mode.
 347 When this mode is enabled,
 348 it emulates 32-bit floating-point operations
 349 by raising a reserved-instruction exception
 350 on every instruction that uses 32-bit formats and
 351 the kernel then handles the instruction in software.
 352 (The problem lies in the discrepancy of handling odd-numbered registers
 353 which are the high 32 bits of 64-bit registers with even numbers in
 354 .B FR=0
 355 mode and the lower 32-bit parts of odd-numbered 64-bit registers in
 356 .B FR=1
 357 mode.)
 358 Enabling this bit is necessary when code with the O32 FP32 ABI should operate
 359 with code with compatible the O32 FPXX or O32 FP64A ABIs (which require
 360 .B FR=1
 361 FPU mode) or when it is executed on newer hardware (MIPS R6 onwards)
 362 which lacks
 363 .B FR=0
 364 mode support when a binary with the FP32 ABI is used.
 365 .IP
 366 Note that this mode makes sense only when the FPU is in 64-bit mode
 367 .RB ( FR=1 ).
 368 .IP
 369 Note that the use of emulation inherently has a significant performance hit
 370 and should be avoided if possible.
 371 .RE
 372 .IP
 373 In the N32/N64 ABI, 64-bit floating-point mode is always used,
 374 so FPU emulation is not required and the FPU always operates in
 375 .B FR=1
 376 mode.
 377 .IP
 378 This option is mainly intended for use by the dynamic linker
 379 .RB ( ld.so (8)).
 380 .IP
 381 The arguments
 382 .IR arg3 ,
 383 .IR arg4 ,
 384 and
 385 .IR arg5
 386 are ignored.
 387 .TP
 388 .BR PR_GET_FP_MODE " (since Linux 4.0, only on MIPS)"
 389 Get the current floating-point mode (see the description of
 390 .B PR_SET_FP_MODE
 391 for details).
 392
 393 On success,
 394 the call returns a bit mask which represents the current floating-point mode.
 395
 396 The arguments
 397 .IR arg2 ,
 398 .IR arg3 ,
 399 .IR arg4 ,
 400 and
 401 .IR arg5
 402 are ignored.
 403 .TP
 404 .BR PR_SET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"
 405 Set floating-point emulation control bits to \fIarg2\fP.
 406 Pass
 407 .B PR_FPEMU_NOPRINT
 408 to silently emulate floating-point operation accesses, or
 409 .B PR_FPEMU_SIGFPE
 410 to not emulate floating-point operations and send
 411 .B SIGFPE
 412 instead.
 413 .TP
 414 .BR PR_GET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"
 415 Return floating-point emulation control bits,
 416 in the location pointed to by
 417 .IR "(int\ *) arg2" .
 418 .TP
 419 .BR PR_SET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"
 420 Set floating-point exception mode to \fIarg2\fP.
 421 Pass \fBPR_FP_EXC_SW_ENABLE\fP to use FPEXC for FP exception enables,
 422 \fBPR_FP_EXC_DIV\fP for floating-point divide by zero,
 423 \fBPR_FP_EXC_OVF\fP for floating-point overflow,
 424 \fBPR_FP_EXC_UND\fP for floating-point underflow,
 425 \fBPR_FP_EXC_RES\fP for floating-point inexact result,
 426 \fBPR_FP_EXC_INV\fP for floating-point invalid operation,
 427 \fBPR_FP_EXC_DISABLED\fP for FP exceptions disabled,
 428 \fBPR_FP_EXC_NONRECOV\fP for async nonrecoverable exception mode,
 429 \fBPR_FP_EXC_ASYNC\fP for async recoverable exception mode,
 430 \fBPR_FP_EXC_PRECISE\fP for precise exception mode.
 431 .TP
 432 .BR PR_GET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"
 433 Return floating-point exception mode,
 434 in the location pointed to by
 435 .IR "(int\ *) arg2" .
 436 .TP
 437 .BR PR_SET_KEEPCAPS " (since Linux 2.2.18)"
 438 Set the state of the calling thread's "keep capabilities" flag,
 439 which determines whether the thread's permitted
 440 capability set is cleared when a change is made to the thread's user IDs
 441 such that the thread's real UID, effective UID, and saved set-user-ID
 442 all become nonzero when at least one of them previously had the value 0.
 443 By default, the permitted capability set is cleared when such a change is made;
 444 setting the "keep capabilities" flag prevents it from being cleared.
 445 .I arg2
 446 must be either 0 (permitted capabilities are cleared)
 447 or 1 (permitted capabilities are kept).
 448 (A thread's
 449 .I effective
 450 capability set is always cleared when such a credential change is made,
 451 regardless of the setting of the "keep capabilities" flag.)
 452 The "keep capabilities" value will be reset to 0 on subsequent calls to
 453 .BR execve (2).
 454 .TP
 455 .BR PR_GET_KEEPCAPS " (since Linux 2.2.18)"
 456 Return (as the function result) the current state of the calling thread's
 457 "keep capabilities" flag.
 458 .TP
 459 .BR PR_MCE_KILL " (since Linux 2.6.32)"
 460 Set the machine check memory corruption kill policy for the calling thread.
 461 If
 462 .I arg2
 463 is
 464 .BR PR_MCE_KILL_CLEAR ,
 465 clear the thread memory corruption kill policy and use the system-wide default.
 466 (The system-wide default is defined by
 467 .IR /proc/sys/vm/memory_failure_early_kill ;
 468 see
 469 .BR proc (5).)
 470 If
 471 .I arg2
 472 is
 473 .BR PR_MCE_KILL_SET ,
 474 use a thread-specific memory corruption kill policy.
 475 In this case,
 476 .I arg3
 477 defines whether the policy is
 478 .I early kill
 479 .RB ( PR_MCE_KILL_EARLY ),
 480 .I late kill
 481 .RB ( PR_MCE_KILL_LATE ),
 482 or the system-wide default
 483 .RB ( PR_MCE_KILL_DEFAULT ).
 484 Early kill means that the thread receives a
 485 .B SIGBUS
 486 signal as soon as hardware memory corruption is detected inside
 487 its address space.
 488 In late kill mode, the process is killed only when it accesses a corrupted page.
 489 See
 490 .BR sigaction (2)
 491 for more information on the
 492 .BR SIGBUS
 493 signal.
 494 The policy is inherited by children.
 495 The remaining unused
 496 .BR prctl ()
 497 arguments must be zero for future compatibility.
 498 .TP
 499 .BR PR_MCE_KILL_GET " (since Linux 2.6.32)"
 500 Return the current per-process machine check kill policy.
 501 All unused
 502 .BR prctl ()
 503 arguments must be zero.
 504 .TP
 505 .BR PR_SET_MM " (since Linux 3.3)"
 506 .\" commit 028ee4be34a09a6d48bdf30ab991ae933a7bc036
 507 Modify certain kernel memory map descriptor fields
 508 of the calling process.
 509 Usually these fields are set by the kernel and dynamic loader (see
 510 .BR ld.so (8)
 511 for more information) and a regular application should not use this feature.
 512 However, there are cases, such as self-modifying programs,
 513 where a program might find it useful to change its own memory map.
 514 This feature is available only if the kernel is built with the
 515 .BR CONFIG_CHECKPOINT_RESTORE
 516 option enabled.
 517 The calling process must have the
 518 .BR CAP_SYS_RESOURCE
 519 capability.
 520 The value in
 521 .I arg2
 522 is one of the options below, while
 523 .I arg3
 524 provides a new value for the option.
 525 .RS
 526 .TP
 527 .BR PR_SET_MM_START_CODE
 528 Set the address above which the program text can run.
 529 The corresponding memory area must be readable and executable,
 530 but not writable or sharable (see
 531 .BR mprotect (2)
 532 and
 533 .BR mmap (2)
 534 for more information).
 535 .TP
 536 .BR PR_SET_MM_END_CODE
 537 Set the address below which the program text can run.
 538 The corresponding memory area must be readable and executable,
 539 but not writable or sharable.
 540 .TP
 541 .BR PR_SET_MM_START_DATA
 542 Set the address above which initialized and
 543 uninitialized (bss) data are placed.
 544 The corresponding memory area must be readable and writable,
 545 but not executable or sharable.
 546 .TP
 547 .B PR_SET_MM_END_DATA
 548 Set the address below which initialized and
 549 uninitialized (bss) data are placed.
 550 The corresponding memory area must be readable and writable,
 551 but not executable or sharable.
 552 .TP
 553 .BR PR_SET_MM_START_STACK
 554 Set the start address of the stack.
 555 The corresponding memory area must be readable and writable.
 556 .TP
 557 .BR PR_SET_MM_START_BRK
 558 Set the address above which the program heap can be expanded with
 559 .BR brk (2)
 560 call.
 561 The address must be greater than the ending address of
 562 the current program data segment.
 563 In addition, the combined size of the resulting heap and
 564 the size of the data segment can't exceed the
 565 .BR RLIMIT_DATA
 566 resource limit (see
 567 .BR setrlimit (2)).
 568 .TP
 569 .BR PR_SET_MM_BRK
 570 Set the current
 571 .BR brk (2)
 572 value.
 573 The requirements for the address are the same as for the
 574 .BR PR_SET_MM_START_BRK
 575 option.
 576 .P
 577 The following options are available since Linux 3.5.
 578 .\" commit fe8c7f5cbf91124987106faa3bdf0c8b955c4cf7
 579 .TP
 580 .BR PR_SET_MM_ARG_START
 581 Set the address above which the program command line is placed.
 582 .TP
 583 .BR PR_SET_MM_ARG_END
 584 Set the address below which the program command line is placed.
 585 .TP
 586 .BR PR_SET_MM_ENV_START
 587 Set the address above which the program environment is placed.
 588 .TP
 589 .BR PR_SET_MM_ENV_END
 590 Set the address below which the program environment is placed.
 591 .IP
 592 The address passed with
 593 .BR PR_SET_MM_ARG_START ,
 594 .BR PR_SET_MM_ARG_END ,
 595 .BR PR_SET_MM_ENV_START ,
 596 and
 597 .BR PR_SET_MM_ENV_END
 598 should belong to a process stack area.
 599 Thus, the corresponding memory area must be readable, writable, and
 600 (depending on the kernel configuration) have the
 601 .BR MAP_GROWSDOWN
 602 attribute set (see
 603 .BR mmap (2)).
 604 .TP
 605 .BR PR_SET_MM_AUXV
 606 Set a new auxiliary vector.
 607 The
 608 .I arg3
 609 argument should provide the address of the vector.
 610 The
 611 .I arg4
 612 is the size of the vector.
 613 .TP
 614 .BR PR_SET_MM_EXE_FILE
 615 .\" commit b32dfe377102ce668775f8b6b1461f7ad428f8b6
 616 Supersede the
 617 .IR /proc/pid/exe
 618 symbolic link with a new one pointing to a new executable file
 619 identified by the file descriptor provided in
 620 .I arg3
 621 argument.
 622 The file descriptor should be obtained with a regular
 623 .BR open (2)
 624 call.
 625 .IP
 626 To change the symbolic link, one needs to unmap all existing
 627 executable memory areas, including those created by the kernel itself
 628 (for example the kernel usually creates at least one executable
 629 memory area for the ELF
 630 .IR \.text
 631 section).
 632 .IP
 633 The second limitation is that such transitions can be done only once
 634 in a process life time.
 635 Any further attempts will be rejected.
 636 This should help system administrators monitor unusual
 637 symbolic-link transitions over all processes running on a system.
 638 .RE
 639 .TP
 640 .BR PR_MPX_ENABLE_MANAGEMENT ", " PR_MPX_DISABLE_MANAGEMENT " (since Linux 3.19) "
 641 .\" commit fe3d197f84319d3bce379a9c0dc17b1f48ad358c
 642 .\" See also http://lwn.net/Articles/582712/
 643 .\" See also https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler
 644 Enable or disable kernel management of Memory Protection eXtensions (MPX)
 645 bounds tables.
 646 The
 647 .IR arg2 ,
 648 .IR arg3 ,
 649 .IR arg4 ,
 650 and
 651 .IR arg5
 652 .\" commit e9d1b4f3c60997fe197bf0243cb4a41a44387a88
 653 arguments must be zero.
 654
 655 MPX is a hardware-assisted mechanism for performing bounds checking on
 656 pointers.
 657 It consists of a set of registers storing bounds information
 658 and a set of special instruction prefixes that tell the CPU on which
 659 instructions it should do bounds enforcement.
 660 There is a limited number of these registers and
 661 when there are more pointers than registers,
 662 their contents must be "spilled" into a set of tables.
 663 These tables are called "bounds tables" and the MPX
 664 .BR prctl ()
 665 operations control
 666 whether the kernel manages their allocation and freeing.
 667
 668 When management is enabled, the kernel will take over allocation
 669 and freeing of the bounds tables.
 670 It does this by trapping the #BR exceptions that result
 671 at first use of missing bounds tables and
 672 instead of delivering the exception to user space,
 673 it allocates the table and populates the bounds directory
 674 with the location of the new table.
 675 For freeing, the kernel checks to see if bounds tables are
 676 present for memory which is not allocated, and frees them if so.
 677
 678 Before enabling MPX management using
 679 .BR PR_MPX_ENABLE_MANAGEMENT ,
 680 the application must first have allocated a user-space buffer for
 681 the bounds directory and placed the location of that directory in the
 682 .I bndcfgu
 683 register.
 684
 685 These calls will fail if the CPU or kernel does not support MPX.
 686 Kernel support for MPX is enabled via the
 687 .BR CONFIG_X86_INTEL_MPX
 688 configuration option.
 689 You can check whether the CPU supports MPX by looking for the 'mpx'
 690 CPUID bit, like with the following command:
 691
 692         cat /proc/cpuinfo | grep ' mpx '
 693
 694 A thread may not switch in or out of long (64-bit) mode while MPX is
 695 enabled.
 696
 697 All threads in a process are affected by these calls.
 698
 699 The child of a
 700 .BR fork (2)
 701 inherits the state of MPX management.
 702 During
 703 .BR execve (2),
 704 MPX management is reset to a state as if
 705 .BR PR_MPX_DISABLE_MANAGEMENT
 706 had been called.
 707
 708 For further information on Intel MPX, see the kernel source file
 709 .IR Documentation/x86/intel_mpx.txt .
 710 .TP
 711 .BR PR_SET_NAME " (since Linux 2.6.9)"
 712 Set the name of the calling thread,
 713 using the value in the location pointed to by
 714 .IR "(char\ *) arg2" .
 715 The name can be up to 16 bytes long,
 716 .\" TASK_COMM_LEN in include/linux/sched.h
 717 including the terminating null byte.
 718 (If the length of the string, including the terminating null byte,
 719 exceeds 16 bytes, the string is silently truncated.)
 720 This is the same attribute that can be set via
 721 .BR pthread_setname_np (3)
 722 and retrieved using
 723 .BR pthread_getname_np (3).
 724 The attribute is likewise accessible via
 725 .IR /proc/self/task/[tid]/comm ,
 726 where
 727 .I tid
 728 is the name of the calling thread.
 729 .TP
 730 .BR PR_GET_NAME " (since Linux 2.6.11)"
 731 Return the name of the calling thread,
 732 in the buffer pointed to by
 733 .IR "(char\ *) arg2" .
 734 The buffer should allow space for up to 16 bytes;
 735 the returned string will be null-terminated.
 736 .TP
 737 .BR PR_SET_NO_NEW_PRIVS " (since Linux 3.5)"
 738 Set the calling thread's
 739 .I no_new_privs
 740 bit to the value in
 741 .IR arg2 .
 742 With
 743 .I no_new_privs
 744 set to 1,
 745 .BR execve (2)
 746 promises not to grant privileges to do anything
 747 that could not have been done without the
 748 .BR execve (2)
 749 call (for example,
 750 rendering the set-user-ID and set-group-ID mode bits,
 751 and file capabilities non-functional).
 752 Once set, this bit cannot be unset.
 753 The setting of this bit is inherited by children created by
 754 .BR fork (2)
 755 and
 756 .BR clone (2),
 757 and preserved across
 758 .BR execve (2).
 759
 760 Since Linux 4.10,
 761 the value of a thread's
 762 .I no_new_privs
 763 bit can be viewed via the
 764 .I NoNewPrivs
 765 field in the
 766 .IR /proc/[pid]/status
 767 file.
 768
 769 For more information, see the kernel source file
 770 .IR Documentation/prctl/no_new_privs.txt .
 771 See also
 772 .BR seccomp (2).
 773 .TP
 774 .BR PR_GET_NO_NEW_PRIVS " (since Linux 3.5)"
 775 Return (as the function result) the value of the
 776 .I no_new_privs
 777 bit for the calling thread.
 778 A value of 0 indicates the regular
 779 .BR execve (2)
 780 behavior.
 781 A value of 1 indicates
 782 .BR execve (2)
 783 will operate in the privilege-restricting mode described above.
 784 .TP
 785 .BR PR_SET_PDEATHSIG " (since Linux 2.1.57)"
 786 Set the parent death signal
 787 of the calling process to \fIarg2\fP (either a signal value
 788 in the range 1..maxsig, or 0 to clear).
 789 This is the signal that the calling process will get when its
 790 parent dies.
 791 This value is cleared for the child of a
 792 .BR fork (2)
 793 and (since Linux 2.4.36 / 2.6.23)
 794 when executing a set-user-ID or set-group-ID binary,
 795 or a binary that has associated capabilities (see
 796 .BR capabilities (7)).
 797 This value is preserved across
 798 .BR execve (2).
 799
 800 .IR Warning :
 801 .\" https://bugzilla.kernel.org/show_bug.cgi?id=43300
 802 the "parent" in this case is considered to be the
 803 .I thread
 804 that created this process.
 805 In other words, the signal will be sent when that thread terminates
 806 (via, for example,
 807 .BR pthread_exit (3)),
 808 rather than after all of the threads in the parent process terminate.
 809 .TP
 810 .BR PR_GET_PDEATHSIG " (since Linux 2.3.15)"
 811 Return the current value of the parent process death signal,
 812 in the location pointed to by
 813 .IR "(int\ *) arg2" .
 814 .TP
 815 .BR PR_SET_PTRACER " (since Linux 3.4)"
 816 .\" commit 2d514487faf188938a4ee4fb3464eeecfbdcf8eb
 817 .\" commit bf06189e4d14641c0148bea16e9dd24943862215
 818 This is meaningful only when the Yama LSM is enabled and in mode 1
 819 ("restricted ptrace", visible via
 820 .IR /proc/sys/kernel/yama/ptrace_scope ).
 821 When a "ptracer process ID" is passed in \fIarg2\fP,
 822 the caller is declaring that the ptracer process can
 823 .BR ptrace (2)
 824 the calling process as if it were a direct process ancestor.
 825 Each
 826 .B PR_SET_PTRACER
 827 operation replaces the previous "ptracer process ID".
 828 Employing
 829 .B PR_SET_PTRACER
 830 with
 831 .I arg2
 832 set to 0 clears the caller's "ptracer process ID".
 833 If
 834 .I arg2
 835 is
 836 .BR PR_SET_PTRACER_ANY ,
 837 the ptrace restrictions introduced by Yama are effectively disabled for the
 838 calling process.
 839
 840 For further information, see the kernel source file
 841 .IR Documentation/security/Yama.txt .
 842 .TP
 843 .BR PR_SET_SECCOMP " (since Linux 2.6.23)"
 844 .\" See http://thread.gmane.org/gmane.linux.kernel/542632
 845 .\" [PATCH 0 of 2] seccomp updates
 846 .\" andrea@cpushare.com
 847 Set the secure computing (seccomp) mode for the calling thread, to limit
 848 the available system calls.
 849 The more recent
 850 .BR seccomp (2)
 851 system call provides a superset of the functionality of
 852 .BR PR_SET_SECCOMP .
 853
 854 The seccomp mode is selected via
 855 .IR arg2 .
 856 (The seccomp constants are defined in
 857 .IR <linux/seccomp.h> .)
 858
 859 With
 860 .IR arg2
 861 set to
 862 .BR SECCOMP_MODE_STRICT ,
 863 the only system calls that the thread is permitted to make are
 864 .BR read (2),
 865 .BR write (2),
 866 .BR _exit (2)
 867 (but not
 868 .BR exit_group (2)),
 869 and
 870 .BR sigreturn (2).
 871 Other system calls result in the delivery of a
 872 .BR SIGKILL
 873 signal.
 874 Strict secure computing mode is useful for number-crunching applications
 875 that may need to execute untrusted byte code,
 876 perhaps obtained by reading from a pipe or socket.
 877 This operation is available only
 878 if the kernel is configured with
 879 .B CONFIG_SECCOMP
 880 enabled.
 881
 882 With
 883 .IR arg2
 884 set to
 885 .BR SECCOMP_MODE_FILTER " (since Linux 3.5),"
 886 the system calls allowed are defined by a pointer
 887 to a Berkeley Packet Filter passed in
 888 .IR arg3 .
 889 This argument is a pointer to
 890 .IR "struct sock_fprog" ;
 891 it can be designed to filter
 892 arbitrary system calls and system call arguments.
 893 This mode is available only if the kernel is configured with
 894 .B CONFIG_SECCOMP_FILTER
 895 enabled.
 896
 897 If
 898 .BR SECCOMP_MODE_FILTER
 899 filters permit
 900 .BR fork (2),
 901 then the seccomp mode is inherited by children created by
 902 .BR fork (2);
 903 if
 904 .BR execve (2)
 905 is permitted, then the seccomp mode is preserved across
 906 .BR execve (2).
 907 If the filters permit
 908 .BR prctl ()
 909 calls, then additional filters can be added;
 910 they are run in order until the first non-allow result is seen.
 911
 912 For further information, see the kernel source file
 913 .IR Documentation/prctl/seccomp_filter.txt .
 914 .TP
 915 .BR PR_GET_SECCOMP " (since Linux 2.6.23)"
 916 Return (as the function result)
 917 the secure computing mode of the calling thread.
 918 If the caller is not in secure computing mode, this operation returns 0;
 919 if the caller is in strict secure computing mode, then the
 920 .BR prctl ()
 921 call will cause a
 922 .B SIGKILL
 923 signal to be sent to the process.
 924 If the caller is in filter mode, and this system call is allowed by the
 925 seccomp filters, it returns 2; otherwise, the process is killed with a
 926 .BR SIGKILL
 927 signal.
 928 This operation is available only
 929 if the kernel is configured with
 930 .B CONFIG_SECCOMP
 931 enabled.
 932
 933 Since Linux 3.8, the
 934 .IR Seccomp
 935 field of the
 936 .IR /proc/[pid]/status
 937 file provides a method of obtaining the same information,
 938 without the risk that the process is killed; see
 939 .BR proc (5).
 940 .TP
 941 .BR PR_SET_SECUREBITS " (since Linux 2.6.26)"
 942 Set the "securebits" flags of the calling thread to the value supplied in
 943 .IR arg2 .
 944 See
 945 .BR capabilities (7).
 946 .TP
 947 .BR PR_GET_SECUREBITS " (since Linux 2.6.26)"
 948 Return (as the function result)
 949 the "securebits" flags of the calling thread.
 950 See
 951 .BR capabilities (7).
 952 .TP
 953 .BR PR_SET_THP_DISABLE " (since Linux 3.15)"
 954 .\" commit a0715cc22601e8830ace98366c0c2bd8da52af52
 955 Set the state of the "THP disable" flag for the calling thread.
 956 If
 957 .I arg2
 958 has a nonzero value, the flag is set, otherwise it is cleared.
 959 Setting this flag provides a method
 960 for disabling transparent huge pages
 961 for jobs where the code cannot be modified, and using a malloc hook with
 962 .BR madvise (2)
 963 is not an option (i.e., statically allocated data).
 964 The setting of the "THP disable" flag is inherited by a child created via
 965 .BR fork (2)
 966 and is preserved across
 967 .BR execve (2).
 968 .\"
 969 .TP
 970 .BR PR_TASK_PERF_EVENTS_DISABLE " (since Linux 2.6.31)"
 971 Disable all performance counters attached to the calling process,
 972 regardless of whether the counters were created by
 973 this process or another process.
 974 Performance counters created by the calling process for other
 975 processes are unaffected.
 976 For more information on performance counters, see the Linux kernel source file
 977 .IR tools/perf/design.txt .
 978 .IP
 979 Originally called
 980 .BR PR_TASK_PERF_COUNTERS_DISABLE ;
 981 .\" commit 1d1c7ddbfab358445a542715551301b7fc363e28
 982 renamed (with same numerical value)
 983 in Linux 2.6.32.
 984 .\"
 985 .TP
 986 .BR PR_TASK_PERF_EVENTS_ENABLE " (since Linux 2.6.31)"
 987 The converse of
 988 .BR PR_TASK_PERF_EVENTS_DISABLE ;
 989 enable performance counters attached to the calling process.
 990 .IP
 991 Originally called
 992 .BR PR_TASK_PERF_COUNTERS_ENABLE ;
 993 .\" commit 1d1c7ddbfab358445a542715551301b7fc363e28
 994 renamed
 995 .\" commit cdd6c482c9ff9c55475ee7392ec8f672eddb7be6
 996 in Linux 2.6.32.
 997 .\"
 998 .TP
 999 .BR PR_GET_THP_DISABLE " (since Linux 3.15)"
1000 Return (via the function result) the current setting of the "THP disable"
1001 flag for the calling thread:
1002 either 1, if the flag is set, or 0, if it is not.
1003 .TP
1004 .BR PR_GET_TID_ADDRESS " (since Linux 3.5)"
1005 .\" commit 300f786b2683f8bb1ec0afb6e1851183a479c86d
1006 Retrieve the
1007 .I clear_child_tid
1008 address set by
1009 .BR set_tid_address (2)
1010 and the
1011 .BR clone (2)
1012 .B CLONE_CHILD_CLEARTID
1013 flag, in the location pointed to by
1014 .IR "(int\ **)\ arg2" .
1015 This feature is available only if the kernel is built with the
1016 .BR CONFIG_CHECKPOINT_RESTORE
1017 option enabled.
1018 Note that since the
1019 .BR prctl ()
1020 system call does not have a compat implementation for
1021 the AMD64 x32 and MIPS n32 ABIs,
1022 and the kernel writes out a pointer using the kernel's pointer size,
1023 this operation expects a user-space buffer of 8 (not 4) bytes on these ABIs.
1024 .TP
1025 .BR PR_SET_TIMERSLACK " (since Linux 2.6.28)"
1026 .\" See https://lwn.net/Articles/369549/
1027 .\" commit 6976675d94042fbd446231d1bd8b7de71a980ada
1028 Each thread has two associated timer slack values:
1029 a "default" value, and a "current" value.
1030 This operation sets the "current" timer slack value for the calling thread.
1031 If the nanosecond value supplied in
1032 .IR arg2
1033 is greater than zero, then the "current" value is set to this value.
1034 If
1035 .I arg2
1036 is less than or equal to zero,
1037 .\" It seems that it's not possible to set the timer slack to zero;
1038 .\" The minimum value is 1? Seems a little strange.
1039 the "current" timer slack is reset to the
1040 thread's "default" timer slack value.
1041
1042 The "current" timer slack is used by the kernel to group timer expirations
1043 for the calling thread that are close to one another;
1044 as a consequence, timer expirations for the thread may be
1045 up to the specified number of nanoseconds late (but will never expire early).
1046 Grouping timer expirations can help reduce system power consumption
1047 by minimizing CPU wake-ups.
1048
1049 The timer expirations affected by timer slack are those set by
1050 .BR select (2),
1051 .BR pselect (2),
1052 .BR poll (2),
1053 .BR ppoll (2),
1054 .BR epoll_wait (2),
1055 .BR epoll_pwait (2),
1056 .BR clock_nanosleep (2),
1057 .BR nanosleep (2),
1058 and
1059 .BR futex (2)
1060 (and thus the library functions implemented via futexes, including
1061 .\" List obtained by grepping for futex usage in glibc source
1062 .BR pthread_cond_timedwait (3),
1063 .BR pthread_mutex_timedlock (3),
1064 .BR pthread_rwlock_timedrdlock (3),
1065 .BR pthread_rwlock_timedwrlock (3),
1066 and
1067 .BR sem_timedwait (3)).
1068
1069 Timer slack is not applied to threads that are scheduled under
1070 a real-time scheduling policy (see
1071 .BR sched_setscheduler (2)).
1072
1073 When a new thread is created,
1074 the two timer slack values are made the same as the "current" value
1075 of the creating thread.
1076 Thereafter, a thread can adjust its "current" timer slack value via
1077 .BR PR_SET_TIMERSLACK .
1078 The "default" value can't be changed.
1079 The timer slack values of
1080 .IR init
1081 (PID 1), the ancestor of all processes,
1082 are 50,000 nanoseconds (50 microseconds).
1083 The timer slack values are preserved across
1084 .BR execve (2).
1085
1086 Since Linux 4.6, the "current" timer slack value of any process
1087 can be examined and changed via the file
1088 .IR /proc/[pid]/timerslack_ns .
1089 See
1090 .BR proc (5).
1091 .TP
1092 .BR PR_GET_TIMERSLACK " (since Linux 2.6.28)"
1093 Return (as the function result)
1094 the "current" timer slack value of the calling thread.
1095 .TP
1096 .BR PR_SET_TIMING " (since Linux 2.6.0-test4)"
1097 Set whether to use (normal, traditional) statistical process timing or
1098 accurate timestamp-based process timing, by passing
1099 .B PR_TIMING_STATISTICAL
1100 .\" 0
1101 or
1102 .B PR_TIMING_TIMESTAMP
1103 .\" 1
1104 to \fIarg2\fP.
1105 .B PR_TIMING_TIMESTAMP
1106 is not currently implemented
1107 (attempting to set this mode will yield the error
1108 .BR EINVAL ).
1109 .\" PR_TIMING_TIMESTAMP doesn't do anything in 2.6.26-rc8,
1110 .\" and looking at the patch history, it appears
1111 .\" that it never did anything.
1112 .TP
1113 .BR PR_GET_TIMING " (since Linux 2.6.0-test4)"
1114 Return (as the function result) which process timing method is currently
1115 in use.
1116 .TP
1117 .BR PR_SET_TSC " (since Linux 2.6.26, x86 only)"
1118 Set the state of the flag determining whether the timestamp counter
1119 can be read by the process.
1120 Pass
1121 .B PR_TSC_ENABLE
1122 to
1123 .I arg2
1124 to allow it to be read, or
1125 .B PR_TSC_SIGSEGV
1126 to generate a
1127 .B SIGSEGV
1128 when the process tries to read the timestamp counter.
1129 .TP
1130 .BR PR_GET_TSC " (since Linux 2.6.26, x86 only)"
1131 Return the state of the flag determining whether the timestamp counter
1132 can be read,
1133 in the location pointed to by
1134 .IR "(int\ *) arg2" .
1135 .TP
1136 .B PR_SET_UNALIGN
1137 (Only on: ia64, since Linux 2.3.48; parisc, since Linux 2.6.15;
1138 PowerPC, since Linux 2.6.18; Alpha, since Linux 2.6.22;
1139 .\" sh: 94ea5e449ae834af058ef005d16a8ad44fcf13d6
1140 .\" tile: 2f9ac29eec71a696cb0dcc5fb82c0f8d4dac28c9
1141 sh, since Linux 2.6.34; tile, since Linux 3.12)
1142 Set unaligned access control bits to \fIarg2\fP.
1143 Pass
1144 \fBPR_UNALIGN_NOPRINT\fP to silently fix up unaligned user accesses,
1145 or \fBPR_UNALIGN_SIGBUS\fP to generate
1146 .B SIGBUS
1147 on unaligned user access.
1148 Alpha also supports an additional flag with the value
1149 of 4 and no corresponding named constant,
1150 which instructs kernel to not fix up
1151 unaligned accesses (it is analogous to providing the
1152 .BR UAC_NOFIX
1153 flag in
1154 .BR SSI_NVPAIRS
1155 operation of the
1156 .BR setsysinfo ()
1157 system call on Tru64).
1158 .TP
1159 .B PR_GET_UNALIGN
1160 (see
1161 .B PR_SET_UNALIGN
1162 for information on versions and architectures)
1163 Return unaligned access control bits, in the location pointed to by
1164 .IR "(unsigned int\ *) arg2" .
1165 .SH RETURN VALUE
1166 On success,
1167 .BR PR_GET_DUMPABLE ,
1168 .BR PR_GET_KEEPCAPS ,
1169 .BR PR_GET_NO_NEW_PRIVS ,
1170 .BR PR_GET_THP_DISABLE ,
1171 .BR PR_CAPBSET_READ ,
1172 .BR PR_GET_TIMING ,
1173 .BR PR_GET_TIMERSLACK ,
1174 .BR PR_GET_SECUREBITS ,
1175 .BR PR_MCE_KILL_GET ,
1176 .BR PR_CAP_AMBIENT + PR_CAP_AMBIENT_IS_SET ,
1177 and (if it returns)
1178 .BR PR_GET_SECCOMP
1179 return the nonnegative values described above.
1180 All other
1181 .I option
1182 values return 0 on success.
1183 On error, \-1 is returned, and
1184 .I errno
1185 is set appropriately.
1186 .SH ERRORS
1187 .TP
1188 .B EACCES
1189 .I option
1190 is
1191 .BR PR_SET_SECCOMP
1192 and
1193 .I arg2
1194 is
1195 .BR SECCOMP_MODE_FILTER ,
1196 but the process does not have the
1197 .BR CAP_SYS_ADMIN
1198 capability or has not set the
1199 .IR no_new_privs
1200 attribute (see the discussion of
1201 .BR PR_SET_NO_NEW_PRIVS
1202 above).
1203 .TP
1204 .B EACCES
1205 .I option
1206 is
1207 .BR PR_SET_MM ,
1208 and
1209 .I arg3
1210 is
1211 .BR PR_SET_MM_EXE_FILE ,
1212 the file is not executable.
1213 .TP
1214 .B EBADF
1215 .I option
1216 is
1217 .BR PR_SET_MM ,
1218 .I arg3
1219 is
1220 .BR PR_SET_MM_EXE_FILE ,
1221 and the file descriptor passed in
1222 .I arg4
1223 is not valid.
1224 .TP
1225 .B EBUSY
1226 .I option
1227 is
1228 .BR PR_SET_MM ,
1229 .I arg3
1230 is
1231 .BR PR_SET_MM_EXE_FILE ,
1232 and this the second attempt to change the
1233 .I /proc/pid/exe
1234 symbolic link, which is prohibited.
1235 .TP
1236 .B EFAULT
1237 .I arg2
1238 is an invalid address.
1239 .TP
1240 .B EFAULT
1241 .I option
1242 is
1243 .BR PR_SET_SECCOMP ,
1244 .I arg2
1245 is
1246 .BR SECCOMP_MODE_FILTER ,
1247 the system was built with
1248 .BR CONFIG_SECCOMP_FILTER ,
1249 and
1250 .I arg3
1251 is an invalid address.
1252 .TP
1253 .B EINVAL
1254 The value of
1255 .I option
1256 is not recognized.
1257 .TP
1258 .B EINVAL
1259 .I option
1260 is
1261 .BR PR_MCE_KILL
1262 or
1263 .BR PR_MCE_KILL_GET
1264 or
1265 .BR PR_SET_MM ,
1266 and unused
1267 .BR prctl ()
1268 arguments were not specified as zero.
1269 .TP
1270 .B EINVAL
1271 .I arg2
1272 is not valid value for this
1273 .IR option .
1274 .TP
1275 .B EINVAL
1276 .I option
1277 is
1278 .BR PR_SET_SECCOMP
1279 or
1280 .BR PR_GET_SECCOMP ,
1281 and the kernel was not configured with
1282 .BR CONFIG_SECCOMP .
1283 .TP
1284 .B EINVAL
1285 .I option
1286 is
1287 .BR PR_SET_SECCOMP ,
1288 .I arg2
1289 is
1290 .BR SECCOMP_MODE_FILTER ,
1291 and the kernel was not configured with
1292 .BR CONFIG_SECCOMP_FILTER .
1293 .TP
1294 .B EINVAL
1295 .I option
1296 is
1297 .BR PR_SET_MM ,
1298 and one of the following is true
1299 .RS
1300 .IP * 3
1301 .I arg4
1302 or
1303 .I arg5
1304 is nonzero;
1305 .IP *
1306 .I arg3
1307 is greater than
1308 .B TASK_SIZE
1309 (the limit on the size of the user address space for this architecture);
1310 .IP *
1311 .I arg2
1312 is
1313 .BR PR_SET_MM_START_CODE ,
1314 .BR PR_SET_MM_END_CODE ,
1315 .BR PR_SET_MM_START_DATA ,
1316 .BR PR_SET_MM_END_DATA ,
1317 or
1318 .BR PR_SET_MM_START_STACK ,
1319 and the permissions of the corresponding memory area are not as required;
1320 .IP *
1321 .I arg2
1322 is
1323 .BR PR_SET_MM_START_BRK
1324 or
1325 .BR PR_SET_MM_BRK ,
1326 and
1327 .I arg3
1328 is less than or equal to the end of the data segment
1329 or specifies a value that would cause the
1330 .B RLIMIT_DATA
1331 resource limit to be exceeded.
1332 .RE
1333 .TP
1334 .B EINVAL
1335 .I option
1336 is
1337 .BR PR_SET_PTRACER
1338 and
1339 .I arg2
1340 is not 0,
1341 .BR PR_SET_PTRACER_ANY ,
1342 or the PID of an existing process.
1343 .TP
1344 .B EINVAL
1345 .I option
1346 is
1347 .B PR_SET_PDEATHSIG
1348 and
1349 .I arg2
1350 is not a valid signal number.
1351 .TP
1352 .B EINVAL
1353 .I option
1354 is
1355 .BR PR_SET_DUMPABLE
1356 and
1357 .I arg2
1358 is neither
1359 .B SUID_DUMP_DISABLE
1360 nor
1361 .BR SUID_DUMP_USER .
1362 .TP
1363 .B EINVAL
1364 .I option
1365 is
1366 .BR PR_SET_TIMING
1367 and
1368 .I arg2
1369 is not
1370 .BR PR_TIMING_STATISTICAL .
1371 .TP
1372 .B EINVAL
1373 .I option
1374 is
1375 .BR PR_SET_NO_NEW_PRIVS
1376 and
1377 .I arg2
1378 is not equal to 1
1379 or
1380 .IR arg3 ,
1381 .IR arg4 ,
1382 or
1383 .IR arg5
1384 is nonzero.
1385 .TP
1386 .B EINVAL
1387 .I option
1388 is
1389 .BR PR_GET_NO_NEW_PRIVS
1390 and
1391 .IR arg2 ,
1392 .IR arg3 ,
1393 .IR arg4 ,
1394 or
1395 .IR arg5
1396 is nonzero.
1397 .TP
1398 .B EINVAL
1399 .I option
1400 is
1401 .BR PR_SET_THP_DISABLE
1402 and
1403 .IR arg3 ,
1404 .IR arg4 ,
1405 or
1406 .IR arg5
1407 is nonzero.
1408 .TP
1409 .B EINVAL
1410 .I option
1411 is
1412 .BR PR_GET_THP_DISABLE
1413 and
1414 .IR arg2 ,
1415 .IR arg3 ,
1416 .IR arg4 ,
1417 or
1418 .IR arg5
1419 is nonzero.
1420 .TP
1421 .B EINVAL
1422 .I option
1423 is
1424 .B PR_CAP_AMBIENT
1425 and an unused argument
1426 .RI ( arg4 ,
1427 .IR arg5 ,
1428 or,
1429 in the case of
1430 .BR PR_CAP_AMBIENT_CLEAR_ALL ,
1431 .IR arg3 )
1432 is nonzero; or
1433 .IR arg2
1434 has an invalid value;
1435 or
1436 .IR arg2
1437 is
1438 .BR PR_CAP_AMBIENT_LOWER ,
1439 .BR PR_CAP_AMBIENT_RAISE ,
1440 or
1441 .BR PR_CAP_AMBIENT_IS_SET
1442 and
1443 .IR arg3
1444 does not specify a valid capability.
1445 .TP
1446 .B ENXIO
1447 .I option
1448 was
1449 .BR PR_MPX_ENABLE_MANAGEMENT
1450 or
1451 .BR PR_MPX_DISABLE_MANAGEMENT
1452 and the kernel or the CPU does not support MPX management.
1453 Check that the kernel and processor have MPX support.
1454 .TP
1455 .B EOPNOTSUPP
1456 .I option
1457 is
1458 .B PR_SET_FP_MODE
1459 and
1460 .I arg2
1461 has an invalid or unsupported value.
1462 .TP
1463 .B EPERM
1464 .I option
1465 is
1466 .BR PR_SET_SECUREBITS ,
1467 and the caller does not have the
1468 .B CAP_SETPCAP
1469 capability,
1470 or tried to unset a "locked" flag,
1471 or tried to set a flag whose corresponding locked flag was set
1472 (see
1473 .BR capabilities (7)).
1474 .TP
1475 .B EPERM
1476 .I option
1477 is
1478 .BR PR_SET_KEEPCAPS ,
1479 and the caller's
1480 .B SECURE_KEEP_CAPS_LOCKED
1481 flag is set
1482 (see
1483 .BR capabilities (7)).
1484 .TP
1485 .B EPERM
1486 .I option
1487 is
1488 .BR PR_CAPBSET_DROP ,
1489 and the caller does not have the
1490 .B CAP_SETPCAP
1491 capability.
1492 .TP
1493 .B EPERM
1494 .I option
1495 is
1496 .BR PR_SET_MM ,
1497 and the caller does not have the
1498 .B CAP_SYS_RESOURCE
1499 capability.
1500 .TP
1501 .B EPERM
1502 .IR option
1503 is
1504 .BR PR_CAP_AMBIENT
1505 and
1506 .IR arg2
1507 is
1508 .BR PR_CAP_AMBIENT_RAISE ,
1509 but either the capability specified in
1510 .IR arg3
1511 is not present in the process's permitted and inheritable capability sets,
1512 or the
1513 .B PR_CAP_AMBIENT_LOWER
1514 securebit has been set.
1515 .SH VERSIONS
1516 The
1517 .BR prctl ()
1518 system call was introduced in Linux 2.1.57.
1519 .\" The library interface was added in glibc 2.0.6
1520 .SH CONFORMING TO
1521 This call is Linux-specific.
1522 IRIX has a
1523 .BR prctl ()
1524 system call (also introduced in Linux 2.1.44
1525 as irix_prctl on the MIPS architecture),
1526 with prototype
1527 .sp
1528 .BI "ptrdiff_t prctl(int " option ", int " arg2 ", int " arg3 );
1529 .sp
1530 and options to get the maximum number of processes per user,
1531 get the maximum number of processors the calling process can use,
1532 find out whether a specified process is currently blocked,
1533 get or set the maximum stack size, and so on.
1534 .SH SEE ALSO
1535 .BR signal (2),
1536 .BR core (5)