.\" Copyright (C) 1998 Andries Brouwer (aeb@cwi.nl)

.\" and Copyright (C) 2002, 2006, 2008, 2012, 2013 Michael Kerrisk <mtk.manpages@gmail.com>

.\" and Copyright Guillem Jover <guillem@hadrons.org>

.\" and Copyright (C) 2014 Dave Hansen / Intel

.\"

.\" %%%LICENSE_START(VERBATIM)

.\" Permission is granted to make and distribute verbatim copies of this

.\" manual provided the copyright notice and this permission notice are

.\" preserved on all copies.

.\"

.\" Permission is granted to copy and distribute modified versions of this

.\" manual under the conditions for verbatim copying, provided that the

.\" entire resulting derived work is distributed under the terms of a

.\" permission notice identical to this one.

.\"

.\" Since the Linux kernel and libraries are constantly changing, this

.\" manual page may be incorrect or out-of-date.  The author(s) assume no

.\" responsibility for errors or omissions, or for damages resulting from

.\" the use of the information contained herein.  The author(s) may not

.\" have taken the same level of care in the production of this manual,

.\" which is licensed free of charge, as they might when working

.\" professionally.

.\"

.\" Formatted or processed versions of this manual, if unaccompanied by

.\" the source, must acknowledge the copyright and authors of this work.

.\" %%%LICENSE_END

.\"

.\" Modified Thu Nov 11 04:19:42 MET 1999, aeb: added PR_GET_PDEATHSIG

.\" Modified 27 Jun 02, Michael Kerrisk

.\" 	Added PR_SET_DUMPABLE, PR_GET_DUMPABLE,

.\"	PR_SET_KEEPCAPS, PR_GET_KEEPCAPS

.\" Modified 2006-08-30 Guillem Jover <guillem@hadrons.org>

.\"	Updated Linux versions where the options where introduced.

.\"	Added PR_SET_TIMING, PR_GET_TIMING, PR_SET_NAME, PR_GET_NAME,

.\"	PR_SET_UNALIGN, PR_GET_UNALIGN, PR_SET_FPEMU, PR_GET_FPEMU,

.\"	PR_SET_FPEXC, PR_GET_FPEXC

.\" 2008-04-29 Serge Hallyn, Document PR_CAPBSET_READ and PR_CAPBSET_DROP

.\" 2008-06-13 Erik Bosman, <ejbosman@cs.vu.nl>

.\"     Document PR_GET_TSC and PR_SET_TSC.

.\" 2008-06-15 mtk, Document PR_SET_SECCOMP, PR_GET_SECCOMP

.\" 2009-10-03 Andi Kleen, document PR_MCE_KILL

.\" 2012-04 Cyrill Gorcunov, Document PR_SET_MM

.\" 2012-04-25 Michael Kerrisk, Document PR_TASK_PERF_EVENTS_DISABLE and

.\"				PR_TASK_PERF_EVENTS_ENABLE

.\" 2012-09-20 Kees Cook, update PR_SET_SECCOMP for mode 2

.\" 2012-09-20 Kees Cook, document PR_SET_NO_NEW_PRIVS, PR_GET_NO_NEW_PRIVS

.\" 2012-10-25 Michael Kerrisk, Document PR_SET_TIMERSLACK and

.\"                             PR_GET_TIMERSLACK

.\" 2013-01-10 Kees Cook, document PR_SET_PTRACER

.\" 2012-02-04 Michael Kerrisk, document PR_{SET,GET}_CHILD_SUBREAPER

.\" 2014-11-10 Dave Hansen, document PR_MPX_{EN,DIS}ABLE_MANAGEMENT

.\"

.\"

.TH PRCTL 2 2018-02-02 "Linux" "Linux Programmer's Manual"

.SH NAME

prctl \- operations on a process

.SH SYNOPSIS

.nf

.B #include <sys/prctl.h>

.PP

.BI "int prctl(int " option ", unsigned long " arg2 ", unsigned long " arg3 ,

.BI "          unsigned long " arg4 ", unsigned long " arg5 );

.fi

.SH DESCRIPTION

.BR prctl ()

is called with a first argument describing what to do

(with values defined in \fI<linux/prctl.h>\fP), and further

arguments with a significance depending on the first one.

The first argument can be:

.\"

.TP

.BR PR_CAP_AMBIENT " (since Linux 4.3)"

.\" commit 58319057b7847667f0c9585b9de0e8932b0fdb08

Reads or changes the ambient capability set of the calling thread,

according to the value of

.IR arg2 ,

which must be one of the following:

.RS

.\"

.TP

.B PR_CAP_AMBIENT_RAISE

The capability specified in

.I arg3

is added to the ambient set.

The specified capability must already be present in

both the permitted and the inheritable sets of the process.

This operation is not permitted if the

.B SECBIT_NO_CAP_AMBIENT_RAISE

securebit is set.

.TP

.B PR_CAP_AMBIENT_LOWER

The capability specified in

.I arg3

is removed from the ambient set.

.TP

.B PR_CAP_AMBIENT_IS_SET

The

.BR prctl ()

call returns 1 if the capability in

.I arg3

is in the ambient set and 0 if it is not.

.TP

.BR PR_CAP_AMBIENT_CLEAR_ALL

All capabilities will be removed from the ambient set.

This operation requires setting

.I arg3

to zero.

.RE

.IP

In all of the above operations,

.I arg4

and

.I arg5

must be specified as 0.

.TP

.BR PR_CAPBSET_READ " (since Linux 2.6.25)"

Return (as the function result) 1 if the capability specified in

.I arg2

is in the calling thread's capability bounding set,

or 0 if it is not.

(The capability constants are defined in

.IR <linux/capability.h> .)

The capability bounding set dictates

whether the process can receive the capability through a

file's permitted capability set on a subsequent call to

.BR execve (2).

.IP

If the capability specified in

.I arg2

is not valid, then the call fails with the error

.BR EINVAL .

.TP

.BR PR_CAPBSET_DROP " (since Linux 2.6.25)"

If the calling thread has the

.B CAP_SETPCAP

capability within its user namespace, then drop the capability specified by

.I arg2

from the calling thread's capability bounding set.

Any children of the calling thread will inherit the newly

reduced bounding set.

.IP

The call fails with the error:

.B EPERM

if the calling thread does not have the

.BR CAP_SETPCAP ;

.BR EINVAL

if

.I arg2

does not represent a valid capability; or

.BR EINVAL

if file capabilities are not enabled in the kernel,

in which case bounding sets are not supported.

.TP

.BR PR_SET_CHILD_SUBREAPER " (since Linux 3.4)"

.\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b

If

.I arg2

is nonzero,

set the "child subreaper" attribute of the calling process;

if

.I arg2

is zero, unset the attribute.

.IP

A subreaper fulfills the role of

.BR init (1)

for its descendant processes.

When a process becomes orphaned

(i.e., its immediate parent terminates)

then that process will be reparented to

the nearest still living ancestor subreaper.

Subsequently, calls to

.BR getppid ()

in the orphaned process will now return the PID of the subreaper process,

and when the orphan terminates, it is the subreaper process that

will receive a

.BR SIGCHLD

signal and will be able to

.BR wait (2)

on the process to discover its termination status.

.IP

The setting of this bit is not inherited by children created by

.BR fork (2)

and

.BR clone (2).

The setting is preserved across

.BR execve (2).

.IP

Establishing a subreaper process is useful in session management frameworks

where a hierarchical group of processes is managed by a subreaper process

that needs to be informed when one of the processes\(emfor example,

a double-forked daemon\(emterminates

(perhaps so that it can restart that process).

Some

.BR init (1)

frameworks (e.g.,

.BR systemd (1))

employ a subreaper process for similar reasons.

.TP

.BR PR_GET_CHILD_SUBREAPER " (since Linux 3.4)"

Return the "child subreaper" setting of the caller,

in the location pointed to by

.IR "(int\ *) arg2" .

.TP

.BR PR_SET_DUMPABLE " (since Linux 2.3.20)"

Set the state of the "dumpable" flag,

which determines whether core dumps are produced for the calling process

upon delivery of a signal whose default behavior is to produce a core dump.

.IP

In kernels up to and including 2.6.12,

.I arg2

must be either 0

.RB ( SUID_DUMP_DISABLE ,

process is not dumpable) or 1

.RB ( SUID_DUMP_USER ,

process is dumpable).

Between kernels 2.6.13 and 2.6.17,

.\" commit abf75a5033d4da7b8a7e92321d74021d1fcfb502

the value 2 was also permitted,

which caused any binary which normally would not be dumped

to be dumped readable by root only;

for security reasons, this feature has been removed.

.\" See http://marc.theaimsgroup.com/?l=linux-kernel&m=115270289030630&w=2

.\" Subject:    Fix prctl privilege escalation (CVE-2006-2451)

.\" From:       Marcel Holtmann <marcel () holtmann ! org>

.\" Date:       2006-07-12 11:12:00

(See also the description of

.I /proc/sys/fs/\:suid_dumpable

in

.BR proc (5).)

.IP

Normally, this flag is set to 1.

However, it is reset to the current value contained in the file

.IR /proc/sys/fs/\:suid_dumpable

(which by default has the value 0),

in the following circumstances:

.\" See kernel/cred.c::commit_creds() (Linux 3.18 sources)

.RS

.IP * 3

The process's effective user or group ID is changed.

.IP *

The process's filesystem user or group ID is changed (see

.BR credentials (7)).

.IP *

The process executes

.RB ( execve (2))

a set-user-ID or set-group-ID program, resulting in a change

of either the effective user ID or the effective group ID.

.IP *

The process executes

.RB ( execve (2))

a program that has file capabilities (see

.BR capabilities (7)),

.\" See kernel/cred.c::commit_creds()

but only if the permitted capabilities

gained exceed those already permitted for the process.

.\" Also certain namespace operations;

.RE

.IP

Processes that are not dumpable can not be attached via

.BR ptrace (2)

.BR PTRACE_ATTACH ;

see

.BR ptrace (2)

for further details.

.IP

If a process is not dumpable,

the ownership of files in the process's

.IR /proc/[pid]

directory is affected as described in

.BR proc (5).

.TP

.BR PR_GET_DUMPABLE " (since Linux 2.3.20)"

Return (as the function result) the current state of the calling

process's dumpable flag.

.\" Since Linux 2.6.13, the dumpable flag can have the value 2,

.\" but in 2.6.13 PR_GET_DUMPABLE simply returns 1 if the dumpable

.\" flags has a nonzero value.  This was fixed in 2.6.14.

.TP

.BR PR_SET_ENDIAN " (since Linux 2.6.18, PowerPC only)"

Set the endian-ness of the calling process to the value given

in \fIarg2\fP, which should be one of the following:

.\" Respectively 0, 1, 2

.BR PR_ENDIAN_BIG ,

.BR PR_ENDIAN_LITTLE ,

or

.B PR_ENDIAN_PPC_LITTLE

(PowerPC pseudo little endian).

.TP

.BR PR_GET_ENDIAN " (since Linux 2.6.18, PowerPC only)"

Return the endian-ness of the calling process,

in the location pointed to by

.IR "(int\ *) arg2" .

.TP

.BR PR_SET_FP_MODE " (since Linux 4.0, only on MIPS)"

.\" commit 9791554b45a2acc28247f66a5fd5bbc212a6b8c8

On the MIPS architecture,

user-space code can be built using an ABI which permits linking

with code that has more restrictive floating-point (FP) requirements.

For example, user-space code may be built to target the O32 FPXX ABI

and linked with code built for either one of the more restrictive

FP32 or FP64 ABIs.

When more restrictive code is linked in,

the overall requirement for the process is to use the more

restrictive floating-point mode.

.IP

Because the kernel has no means of knowing in advance

which mode the process should be executed in,

and because these restrictions can

change over the lifetime of the process, the

.B PR_SET_FP_MODE

operation is provided to allow control of the floating-point mode

from user space.

.IP

.\" https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking

The

.I (unsigned int) arg2

argument is a bit mask describing the floating-point mode used:

.RS

.TP

.BR PR_FP_MODE_FR

When this bit is

.I unset

(so called

.BR FR=0 " or " FR0

mode), the 32 floating-point registers are 32 bits wide,

and 64-bit registers are represented as a pair of registers

(even- and odd- numbered,

with the even-numbered register containing the lower 32 bits,

and the odd-numbered register containing the higher 32 bits).

.IP

When this bit is

.I set

(on supported hardware),

the 32 floating-point registers are 64 bits wide (so called

.BR FR=1 " or " FR1

mode).

Note that modern MIPS implementations (MIPS R6 and newer) support

.B FR=1

mode only.

.IP

.IP

Applications that use the O32 FP32 ABI can operate only when this bit is

.I unset

.RB ( FR=0 ;

or they can be used with FRE enabled, see below).

Applications that use the O32 FP64 ABI

(and the O32 FP64A ABI, which exists to

provide the ability to operate with existing FP32 code; see below)

can operate only when this bit is

.I set

.RB ( FR=1 ).

Applications that use the O32 FPXX ABI can operate with either

.BR FR=0

or

.BR FR=1 .

.TP

.BR PR_FP_MODE_FRE

Enable emulation of 32-bit floating-point mode.

When this mode is enabled,

it emulates 32-bit floating-point operations

by raising a reserved-instruction exception

on every instruction that uses 32-bit formats and

the kernel then handles the instruction in software.

(The problem lies in the discrepancy of handling odd-numbered registers

which are the high 32 bits of 64-bit registers with even numbers in

.B FR=0

mode and the lower 32-bit parts of odd-numbered 64-bit registers in

.B FR=1

mode.)

Enabling this bit is necessary when code with the O32 FP32 ABI should operate

with code with compatible the O32 FPXX or O32 FP64A ABIs (which require

.B FR=1

FPU mode) or when it is executed on newer hardware (MIPS R6 onwards)

which lacks

.B FR=0

mode support when a binary with the FP32 ABI is used.

.IP

Note that this mode makes sense only when the FPU is in 64-bit mode

.RB ( FR=1 ).

.IP

Note that the use of emulation inherently has a significant performance hit

and should be avoided if possible.

.RE

.IP

In the N32/N64 ABI, 64-bit floating-point mode is always used,

so FPU emulation is not required and the FPU always operates in

.B FR=1

mode.

.IP

This option is mainly intended for use by the dynamic linker

.RB ( ld.so (8)).

.IP

The arguments

.IR arg3 ,

.IR arg4 ,

and

.IR arg5

are ignored.

.TP

.BR PR_GET_FP_MODE " (since Linux 4.0, only on MIPS)"

Get the current floating-point mode (see the description of

.B PR_SET_FP_MODE

for details).

.IP

On success,

the call returns a bit mask which represents the current floating-point mode.

.IP

The arguments

.IR arg2 ,

.IR arg3 ,

.IR arg4 ,

and

.IR arg5

are ignored.

.TP

.BR PR_SET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"

Set floating-point emulation control bits to \fIarg2\fP.

Pass

.B PR_FPEMU_NOPRINT

to silently emulate floating-point operation accesses, or

.B PR_FPEMU_SIGFPE

to not emulate floating-point operations and send

.B SIGFPE

instead.

.TP

.BR PR_GET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"

Return floating-point emulation control bits,

in the location pointed to by

.IR "(int\ *) arg2" .

.TP

.BR PR_SET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"

Set floating-point exception mode to \fIarg2\fP.

Pass \fBPR_FP_EXC_SW_ENABLE\fP to use FPEXC for FP exception enables,

\fBPR_FP_EXC_DIV\fP for floating-point divide by zero,

\fBPR_FP_EXC_OVF\fP for floating-point overflow,

\fBPR_FP_EXC_UND\fP for floating-point underflow,

\fBPR_FP_EXC_RES\fP for floating-point inexact result,

\fBPR_FP_EXC_INV\fP for floating-point invalid operation,

\fBPR_FP_EXC_DISABLED\fP for FP exceptions disabled,

\fBPR_FP_EXC_NONRECOV\fP for async nonrecoverable exception mode,

\fBPR_FP_EXC_ASYNC\fP for async recoverable exception mode,

\fBPR_FP_EXC_PRECISE\fP for precise exception mode.

.TP

.BR PR_GET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"

Return floating-point exception mode,

in the location pointed to by

.IR "(int\ *) arg2" .

.TP

.BR PR_SET_KEEPCAPS " (since Linux 2.2.18)"

Set the state of the calling thread's "keep capabilities" flag.

The effect if this flag is described in

.BR capabilities (7).

.I arg2

must be either 0 (clear the flag)

or 1 (set the flag).

The "keep capabilities" value will be reset to 0 on subsequent calls to

.BR execve (2).

.TP

.BR PR_GET_KEEPCAPS " (since Linux 2.2.18)"

Return (as the function result) the current state of the calling thread's

"keep capabilities" flag.

See

.BR capabilities (7)

for a description of this flag.

.TP

.BR PR_MCE_KILL " (since Linux 2.6.32)"

Set the machine check memory corruption kill policy for the calling thread.

If

.I arg2

is

.BR PR_MCE_KILL_CLEAR ,

clear the thread memory corruption kill policy and use the system-wide default.

(The system-wide default is defined by

.IR /proc/sys/vm/memory_failure_early_kill ;

see

.BR proc (5).)

If

.I arg2

is

.BR PR_MCE_KILL_SET ,

use a thread-specific memory corruption kill policy.

In this case,

.I arg3

defines whether the policy is

.I early kill

.RB ( PR_MCE_KILL_EARLY ),

.I late kill

.RB ( PR_MCE_KILL_LATE ),

or the system-wide default

.RB ( PR_MCE_KILL_DEFAULT ).

Early kill means that the thread receives a

.B SIGBUS

signal as soon as hardware memory corruption is detected inside

its address space.

In late kill mode, the process is killed only when it accesses a corrupted page.

See

.BR sigaction (2)

for more information on the

.BR SIGBUS

signal.

The policy is inherited by children.

The remaining unused

.BR prctl ()

arguments must be zero for future compatibility.

.TP

.BR PR_MCE_KILL_GET " (since Linux 2.6.32)"

Return the current per-process machine check kill policy.

All unused

.BR prctl ()

arguments must be zero.

.TP

.BR PR_SET_MM " (since Linux 3.3)"

.\" commit 028ee4be34a09a6d48bdf30ab991ae933a7bc036

Modify certain kernel memory map descriptor fields

of the calling process.

Usually these fields are set by the kernel and dynamic loader (see

.BR ld.so (8)

for more information) and a regular application should not use this feature.

However, there are cases, such as self-modifying programs,

where a program might find it useful to change its own memory map.

.IP

The calling process must have the

.BR CAP_SYS_RESOURCE

capability.

The value in

.I arg2

is one of the options below, while

.I arg3

provides a new value for the option.

The

.I arg4

and

.I arg5

arguments must be zero if unused.

.IP

.\" commit 52b3694157e3aa6df871e283115652ec6f2d31e0

Since Linux 3.10,

this feature is available all the time.

Before Linux 3.10,

this feature is available only if the kernel is built with the

.BR CONFIG_CHECKPOINT_RESTORE

option enabled.

.RS

.TP

.BR PR_SET_MM_START_CODE

Set the address above which the program text can run.

The corresponding memory area must be readable and executable,

but not writable or shareable (see

.BR mprotect (2)

and

.BR mmap (2)

for more information).

.TP

.BR PR_SET_MM_END_CODE

Set the address below which the program text can run.

The corresponding memory area must be readable and executable,

but not writable or shareable.

.TP

.BR PR_SET_MM_START_DATA

Set the address above which initialized and

uninitialized (bss) data are placed.

The corresponding memory area must be readable and writable,

but not executable or shareable.

.TP

.B PR_SET_MM_END_DATA

Set the address below which initialized and

uninitialized (bss) data are placed.

The corresponding memory area must be readable and writable,

but not executable or shareable.

.TP

.BR PR_SET_MM_START_STACK

Set the start address of the stack.

The corresponding memory area must be readable and writable.

.TP

.BR PR_SET_MM_START_BRK

Set the address above which the program heap can be expanded with

.BR brk (2)

call.

The address must be greater than the ending address of

the current program data segment.

In addition, the combined size of the resulting heap and

the size of the data segment can't exceed the

.BR RLIMIT_DATA

resource limit (see

.BR setrlimit (2)).

.TP

.BR PR_SET_MM_BRK

Set the current

.BR brk (2)

value.

The requirements for the address are the same as for the

.BR PR_SET_MM_START_BRK

option.

.PP

The following options are available since Linux 3.5.

.\" commit fe8c7f5cbf91124987106faa3bdf0c8b955c4cf7

.TP

.BR PR_SET_MM_ARG_START

Set the address above which the program command line is placed.

.TP

.BR PR_SET_MM_ARG_END

Set the address below which the program command line is placed.

.TP

.BR PR_SET_MM_ENV_START

Set the address above which the program environment is placed.

.TP

.BR PR_SET_MM_ENV_END

Set the address below which the program environment is placed.

.IP

The address passed with

.BR PR_SET_MM_ARG_START ,

.BR PR_SET_MM_ARG_END ,

.BR PR_SET_MM_ENV_START ,

and

.BR PR_SET_MM_ENV_END

should belong to a process stack area.

Thus, the corresponding memory area must be readable, writable, and

(depending on the kernel configuration) have the

.BR MAP_GROWSDOWN

attribute set (see

.BR mmap (2)).

.TP

.BR PR_SET_MM_AUXV

Set a new auxiliary vector.

The

.I arg3

argument should provide the address of the vector.

The

.I arg4

is the size of the vector.

.TP

.BR PR_SET_MM_EXE_FILE

.\" commit b32dfe377102ce668775f8b6b1461f7ad428f8b6

Supersede the

.IR /proc/pid/exe

symbolic link with a new one pointing to a new executable file

identified by the file descriptor provided in

.I arg3

argument.

The file descriptor should be obtained with a regular

.BR open (2)

call.

.IP

To change the symbolic link, one needs to unmap all existing

executable memory areas, including those created by the kernel itself

(for example the kernel usually creates at least one executable

memory area for the ELF

.IR \.text

section).

.IP

The second limitation is that such transitions can be done only once

in a process life time.

Any further attempts will be rejected.

This should help system administrators monitor unusual

symbolic-link transitions over all processes running on a system.

.PP

The following options are available since Linux 3.18.

.\" commit f606b77f1a9e362451aca8f81d8f36a3a112139e

.TP

.BR PR_SET_MM_MAP

Provides one-shot access to all the addresses by passing in a

.I struct prctl_mm_map

(as defined in \fI<linux/prctl.h>\fP).

The

.I arg4

argument should provide the size of the struct.

.IP

This feature is available only if the kernel is built with the

.BR CONFIG_CHECKPOINT_RESTORE

option enabled.

.TP

.BR PR_SET_MM_MAP_SIZE

Returns the size of the

.I struct prctl_mm_map

the kernel expects.

This allows user space to find a compatible struct.

The

.I arg4

argument should be a pointer to an unsigned int.

.IP

This feature is available only if the kernel is built with the

.BR CONFIG_CHECKPOINT_RESTORE

option enabled.

.RE

.TP

.BR PR_MPX_ENABLE_MANAGEMENT ", " PR_MPX_DISABLE_MANAGEMENT " (since Linux 3.19) "

.\" commit fe3d197f84319d3bce379a9c0dc17b1f48ad358c

.\" See also http://lwn.net/Articles/582712/

.\" See also https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler

Enable or disable kernel management of Memory Protection eXtensions (MPX)

bounds tables.

The

.IR arg2 ,

.IR arg3 ,

.IR arg4 ,

and

.IR arg5

.\" commit e9d1b4f3c60997fe197bf0243cb4a41a44387a88

arguments must be zero.

.IP

MPX is a hardware-assisted mechanism for performing bounds checking on

pointers.

It consists of a set of registers storing bounds information

and a set of special instruction prefixes that tell the CPU on which

instructions it should do bounds enforcement.

There is a limited number of these registers and

when there are more pointers than registers,

their contents must be "spilled" into a set of tables.

These tables are called "bounds tables" and the MPX

.BR prctl ()

operations control

whether the kernel manages their allocation and freeing.

.IP

When management is enabled, the kernel will take over allocation

and freeing of the bounds tables.

It does this by trapping the #BR exceptions that result

at first use of missing bounds tables and

instead of delivering the exception to user space,

it allocates the table and populates the bounds directory

with the location of the new table.

For freeing, the kernel checks to see if bounds tables are

present for memory which is not allocated, and frees them if so.

.IP

Before enabling MPX management using

.BR PR_MPX_ENABLE_MANAGEMENT ,

the application must first have allocated a user-space buffer for

the bounds directory and placed the location of that directory in the

.I bndcfgu

register.

.IP

These calls fail if the CPU or kernel does not support MPX.

Kernel support for MPX is enabled via the

.BR CONFIG_X86_INTEL_MPX

configuration option.

You can check whether the CPU supports MPX by looking for the 'mpx'

CPUID bit, like with the following command:

.IP

	cat /proc/cpuinfo | grep ' mpx '

.IP

A thread may not switch in or out of long (64-bit) mode while MPX is

enabled.

.IP

All threads in a process are affected by these calls.

.IP

The child of a

.BR fork (2)

inherits the state of MPX management.

During

.BR execve (2),

MPX management is reset to a state as if

.BR PR_MPX_DISABLE_MANAGEMENT

had been called.

.IP

For further information on Intel MPX, see the kernel source file

.IR Documentation/x86/intel_mpx.txt .

.TP

.BR PR_SET_NAME " (since Linux 2.6.9)"

Set the name of the calling thread,

using the value in the location pointed to by

.IR "(char\ *) arg2" .

The name can be up to 16 bytes long,

.\" TASK_COMM_LEN in include/linux/sched.h

including the terminating null byte.

(If the length of the string, including the terminating null byte,

exceeds 16 bytes, the string is silently truncated.)

This is the same attribute that can be set via

.BR pthread_setname_np (3)

and retrieved using

.BR pthread_getname_np (3).

The attribute is likewise accessible via

.IR /proc/self/task/[tid]/comm ,

where

.I tid

is the name of the calling thread.

.TP

.BR PR_GET_NAME " (since Linux 2.6.11)"

Return the name of the calling thread,

in the buffer pointed to by

.IR "(char\ *) arg2" .

The buffer should allow space for up to 16 bytes;

the returned string will be null-terminated.

.TP

.BR PR_SET_NO_NEW_PRIVS " (since Linux 3.5)"

Set the calling thread's

.I no_new_privs

bit to the value in

.IR arg2 .

With

.I no_new_privs

set to 1,

.BR execve (2)

promises not to grant privileges to do anything

that could not have been done without the

.BR execve (2)

call (for example,

rendering the set-user-ID and set-group-ID mode bits,

and file capabilities non-functional).

Once set, this bit cannot be unset.

The setting of this bit is inherited by children created by

.BR fork (2)

and

.BR clone (2),

and preserved across

.BR execve (2).

.IP

Since Linux 4.10,

the value of a thread's

.I no_new_privs

bit can be viewed via the

.I NoNewPrivs

field in the

.IR /proc/[pid]/status

file.

.IP

For more information, see the kernel source file

.IR Documentation/userspace\-api/no_new_privs.rst

.\" commit 40fde647ccb0ae8c11d256d271e24d385eed595b

(or

.IR Documentation/prctl/no_new_privs.txt

before Linux 4.13).

See also

.BR seccomp (2).

.TP

.BR PR_GET_NO_NEW_PRIVS " (since Linux 3.5)"

Return (as the function result) the value of the

.I no_new_privs

bit for the calling thread.

A value of 0 indicates the regular

.BR execve (2)

behavior.

A value of 1 indicates

.BR execve (2)

will operate in the privilege-restricting mode described above.

.TP

.BR PR_SET_PDEATHSIG " (since Linux 2.1.57)"

Set the parent death signal

of the calling process to \fIarg2\fP (either a signal value

in the range 1..maxsig, or 0 to clear).

This is the signal that the calling process will get when its

parent dies.

This value is cleared for the child of a

.BR fork (2)

and (since Linux 2.4.36 / 2.6.23)

when executing a set-user-ID or set-group-ID binary,

or a binary that has associated capabilities (see

.BR capabilities (7)).

This value is preserved across

.BR execve (2).

.IP

.IR Warning :

.\" https://bugzilla.kernel.org/show_bug.cgi?id=43300

the "parent" in this case is considered to be the

.I thread

that created this process.

In other words, the signal will be sent when that thread terminates

(via, for example,

.BR pthread_exit (3)),

rather than after all of the threads in the parent process terminate.

.TP

.BR PR_GET_PDEATHSIG " (since Linux 2.3.15)"

Return the current value of the parent process death signal,

in the location pointed to by

.IR "(int\ *) arg2" .

.TP

.BR PR_SET_PTRACER " (since Linux 3.4)"

.\" commit 2d514487faf188938a4ee4fb3464eeecfbdcf8eb

.\" commit bf06189e4d14641c0148bea16e9dd24943862215

This is meaningful only when the Yama LSM is enabled and in mode 1

("restricted ptrace", visible via

.IR /proc/sys/kernel/yama/ptrace_scope ).

When a "ptracer process ID" is passed in \fIarg2\fP,

the caller is declaring that the ptracer process can

.BR ptrace (2)

the calling process as if it were a direct process ancestor.

Each

.B PR_SET_PTRACER

operation replaces the previous "ptracer process ID".

Employing

.B PR_SET_PTRACER

with