.\" 2014-11-10 Dave Hansen, document PR_MPX_{EN,DIS}ABLE_MANAGEMENT
.\"
.\"
-.TH PRCTL 2 2017-09-15 "Linux" "Linux Programmer's Manual"
+.TH PRCTL 2 2019-08-02 "Linux" "Linux Programmer's Manual"
.SH NAME
prctl \- operations on a process
.SH SYNOPSIS
and
.I arg5
must be specified as 0.
+.IP
+Higher-level interfaces layered on top of the above operations are
+provided in the
+.BR libcap (3)
+library in the form of
+.BR cap_get_ambient (3),
+.BR cap_set_ambient (3),
+and
+.BR cap_reset_ambient (3).
.TP
.BR PR_CAPBSET_READ " (since Linux 2.6.25)"
Return (as the function result) 1 if the capability specified in
.I arg2
is not valid, then the call fails with the error
.BR EINVAL .
+.IP
+A higher-level interface layered on top of this operation is provided in the
+.BR libcap (3)
+library in the form of
+.BR cap_get_bound (3).
.TP
.BR PR_CAPBSET_DROP " (since Linux 2.6.25)"
If the calling thread has the
.BR EINVAL
if file capabilities are not enabled in the kernel,
in which case bounding sets are not supported.
+.IP
+A higher-level interface layered on top of this operation is provided in the
+.BR libcap (3)
+library in the form of
+.BR cap_drop_bound (3).
.TP
.BR PR_SET_CHILD_SUBREAPER " (since Linux 3.4)"
.\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b
.BR wait (2)
on the process to discover its termination status.
.IP
-The setting of this bit is not inherited by children created by
+The setting of the "child subreaper" attribute
+is not inherited by children created by
.BR fork (2)
and
.BR clone (2).
.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
+The effect of this flag is described in
.BR capabilities (7).
.I arg2
must be either 0 (clear the flag)
.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,
+.\" commit 52b3694157e3aa6df871e283115652ec6f2d31e0
this feature is available only if the kernel is built with the
.BR CONFIG_CHECKPOINT_RESTORE
option enabled.
.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.
+In Linux 4.9 and earlier, the
+.\" commit 3fb4afd9a504c2386b8435028d43283216bf588e
+.BR PR_SET_MM_EXE_FILE
+operation can be performed only once in a process's lifetime;
+attempting to perform the operation a second time results in the error
+.BR EPERM .
+This restriction was enforced for security reasons that were subsequently
+deemed specious,
+and the restriction was removed in Linux 4.10 because some
+user-space applications needed to perform this operation more than once.
.PP
The following options are available since Linux 3.18.
.\" commit f606b77f1a9e362451aca8f81d8f36a3a112139e
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 '
+.in +4n
+.EX
+cat /proc/cpuinfo | grep ' mpx '
+.EE
+.in
.IP
A thread may not switch in or out of long (64-bit) mode while MPX is
enabled.
.BR PR_SET_NO_NEW_PRIVS " (since Linux 3.5)"
Set the calling thread's
.I no_new_privs
-bit to the value in
+attribute to the value in
.IR arg2 .
With
.I no_new_privs
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
+Once set, this the
+.I no_new_privs
+attribute cannot be unset.
+The setting of this attribute is inherited by children created by
.BR fork (2)
and
.BR clone (2),
Since Linux 4.10,
the value of a thread's
.I no_new_privs
-bit can be viewed via the
+attribute can be viewed via the
.I NoNewPrivs
field in the
.IR /proc/[pid]/status
.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.
+attribute for the calling thread.
A value of 0 indicates the regular
.BR execve (2)
behavior.
will operate in the privilege-restricting mode described above.
.TP
.BR PR_SET_PDEATHSIG " (since Linux 2.1.57)"
-Set the parent death signal
+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
(via, for example,
.BR pthread_exit (3)),
rather than after all of the threads in the parent process terminate.
+.IP
+The parent-death signal is sent upon subsequent termination of the parent
+thread and also upon termination of each subreaper process
+(see the description of
+.B PR_SET_CHILD_SUBREAPER
+above) to which the caller is subsequently reparented.
+If the parent thread and all ancestor subreapers have already terminated
+by the time of the
+.BR PR_SET_PDEATHSIG
+operation, then no parent-death signal is sent to the caller.
+.IP
+The parent-death signal is process-directed (see
+.BR signal (7))
+and, if the child installs a handler using the
+.BR sigaction (2)
+.B SA_SIGINFO
+flag, the
+.I si_pid
+field of the
+.I siginfo_t
+argument of the handler contains the PID of the terminating parent process.
+.IP
+The parent-death signal setting is cleared for the child of a
+.BR fork (2).
+It is also
+(since Linux 2.4.36 / 2.6.23)
+.\" commit d2d56c5f51028cb9f3d800882eb6f4cbd3f9099f
+cleared when executing a set-user-ID or set-group-ID binary,
+or a binary that has associated capabilities (see
+.BR capabilities (7));
+otherwise, this value is preserved across
+.BR execve (2).
.TP
.BR PR_GET_PDEATHSIG " (since Linux 2.3.15)"
Return the current value of the parent process death signal,
See
.BR capabilities (7).
.TP
+.BR PR_GET_SPECULATION_CTRL " (since Linux 4.17)"
+Returns the state of the speculation misfeature specified in
+.IR arg2 .
+Currently, the only permitted value for this argument is
+.BR PR_SPEC_STORE_BYPASS
+(otherwise the call fails with the error
+.BR ENODEV ).
+.IP
+The return value uses bits 0-3 with the following meaning:
+.RS
+.TP
+.BR PR_SPEC_PRCTL
+Mitigation can be controlled per thread by
+.B PR_SET_SPECULATION_CTRL
+.TP
+.BR PR_SPEC_ENABLE
+The speculation feature is enabled, mitigation is disabled.
+.TP
+.BR PR_SPEC_DISABLE
+The speculation feature is disabled, mitigation is enabled
+.TP
+.BR PR_SPEC_FORCE_DISABLE
+Same as
+.B PR_SPEC_DISABLE
+but cannot be undone.
+.RE
+.IP
+If all bits are 0,
+then the CPU is not affected by the speculation misfeature.
+.IP
+If
+.B PR_SPEC_PRCTL
+is set, then per-thread control of the mitigation is available.
+If not set,
+.BR prctl ()
+for the speculation misfeature will fail.
+.IP
+The
+.IR arg3 ,
+.IR arg4 ,
+and
+.I arg5
+arguments must be specified as 0; otherwise the call fails with the error
+.BR EINVAL .
+.TP
+.BR PR_SET_SPECULATION_CTRL " (since Linux 4.17)"
+.\" commit b617cfc858161140d69cc0b5cc211996b557a1c7
+.\" commit 356e4bfff2c5489e016fdb925adbf12a1e3950ee
+Sets the state of the speculation misfeature specified in
+.IR arg2 .
+Currently, the only permitted value for this argument is
+.B PR_SPEC_STORE_BYPASS
+(otherwise the call fails with the error
+.BR ENODEV ).
+This setting is a per-thread attribute.
+The
+.IR arg3
+argument is used to hand in the control value,
+which is one of the following:
+.RS
+.TP
+.BR PR_SPEC_ENABLE
+The speculation feature is enabled, mitigation is disabled.
+.TP
+.BR PR_SPEC_DISABLE
+The speculation feature is disabled, mitigation is enabled
+.TP
+.BR PR_SPEC_FORCE_DISABLE
+Same as
+.B PR_SPEC_DISABLE
+but cannot be undone.
+A subsequent
+.B
+prctl(..., PR_SPEC_ENABLE)
+will fail with the error
+.BR EPERM .
+.RE
+.IP
+Any other value in
+.IR arg3
+will result in the call failing with the error
+.BR ERANGE .
+.IP
+The
+.I arg4
+and
+.I arg5
+arguments must be specified as 0; otherwise the call fails with the error
+.BR EINVAL .
+.IP
+The speculation feature can also be controlled by the
+.B spec_store_bypass_disable
+boot parameter.
+This parameter may enforce a read-only policy which will result in the
+.BR prctl (2)
+call failing with the error
+.BR ENXIO .
+For further details, see the kernel source file
+.IR Documentation/admin-guide/kernel-parameters.txt .
+.TP
.BR PR_SET_THP_DISABLE " (since Linux 3.15)"
.\" commit a0715cc22601e8830ace98366c0c2bd8da52af52
Set the state of the "THP disable" flag for the calling thread.
Each thread has two associated timer slack values:
a "default" value, and a "current" value.
This operation sets the "current" timer slack value for the calling thread.
+.I arg2
+is an unsigned long value, then maximum "current" value is ULONG_MAX and
+the minimum "current" value is 1.
If the nanosecond value supplied in
.IR arg2
is greater than zero, then the "current" value is set to this value.
If
.I arg2
-is less than or equal to zero,
-.\" It seems that it's not possible to set the timer slack to zero;
-.\" The minimum value is 1? Seems a little strange.
+is equal to zero,
the "current" timer slack is reset to the
thread's "default" timer slack value.
.IP
.IR init
(PID 1), the ancestor of all processes,
are 50,000 nanoseconds (50 microseconds).
-The timer slack values are preserved across
+The timer slack value is inherited by a child created via
+.BR fork(2),
+and is preserved across
.BR execve (2).
.IP
Since Linux 4.6, the "current" timer slack value of any process
Return (as the function result)
the "current" timer slack value of the calling thread.
.TP
-.BR PR_SET_TIMING " (since Linux 2.6.0-test4)"
+.BR PR_SET_TIMING " (since Linux 2.6.0)"
+.\" Precisely: Linux 2.6.0-test4
Set whether to use (normal, traditional) statistical process timing or
accurate timestamp-based process timing, by passing
.B PR_TIMING_STATISTICAL
.\" and looking at the patch history, it appears
.\" that it never did anything.
.TP
-.BR PR_GET_TIMING " (since Linux 2.6.0-test4)"
+.BR PR_GET_TIMING " (since Linux 2.6.0)"
+.\" Precisely: Linux 2.6.0-test4
Return (as the function result) which process timing method is currently
in use.
.TP
.IR arg3
does not specify a valid capability.
.TP
+.B ENODEV
+.I option
+was
+.BR PR_SET_SPECULATION_CTRL
+the kernel or CPU does not support the requested speculation misfeature.
+.TP
.B ENXIO
.I option
was
and the kernel or the CPU does not support MPX management.
Check that the kernel and processor have MPX support.
.TP
+.B ENXIO
+.I option
+was
+.BR PR_SET_SPECULATION_CTRL
+implies that the control of the selected speculation misfeature is not possible.
+See
+.BR PR_GET_SPECULATION_CTRL
+for the bit fields to determine which option is available.
+.TP
.B EOPNOTSUPP
.I option
is
.B EPERM
.I option
is
+.BR PR_SET_SPECULATION_CTRL
+wherein the speculation was disabled with
+.B PR_SPEC_FORCE_DISABLE
+and caller tried to enable it again.
+.TP
+.B EPERM
+.I option
+is
.BR PR_SET_KEEPCAPS ,
and the caller's
-.B SECURE_KEEP_CAPS_LOCKED
+.B SECBIT_KEEP_CAPS_LOCKED
flag is set
(see
.BR capabilities (7)).
or the
.B PR_CAP_AMBIENT_LOWER
securebit has been set.
+.TP
+.B ERANGE
+.I option
+was
+.BR PR_SET_SPECULATION_CTRL
+and
+.IR arg3
+is neither
+.BR PR_SPEC_ENABLE ,
+.BR PR_SPEC_DISABLE ,
+nor
+.BR PR_SPEC_FORCE_DISABLE .
+.TP
+.B EINVAL
+.I option
+was
+.BR PR_GET_SPECULATION_CTRL
+or
+.BR PR_SET_SPECULATION_CTRL
+and unused arguments to
+.BR prctl ()
+are not 0.
.SH VERSIONS
The
.BR prctl ()
projects / thirdparty / man-pages.git / blobdiff