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prctl.2: Some tweaks to Dave Handsen's patch 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2015-01-10 15:15:03 +01:00
parent 0397979417
commit 3cd5e9837f
1 changed files with 38 additions and 27 deletions
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65
man2/prctl.2
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@ -1,6 +1,7 @@
.\" 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
@ -817,35 +818,42 @@ This should help system administrators monitor unusual
symbolic-link transitions over all processes running on a system.
.RE
.TP
.BR PR_MPX_ENABLE_MANAGEMENT / PR_MPX_DISABLE_MANAGEMENT " (since Linux 3.19) "
.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
Control the kernel's management of Memory Protection eXtensions (MPX)
Enable or disable kernel management of Memory Protection eXtensions (MPX)
bounds tables.
MPX is a hardware-assisted mechanism for performing bounds checking on
pointers. It consists of a set of registers storing bounds information
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" in to a set of tables.
These tables are called "bounds tables" and these prctl()s control
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.
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 userspace, 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
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.
Before enabling MPX management using PR_MPX_ENABLE_MANAGEMENT,
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 bndcfgu register.
the bounds directory and placed the location of that directory in the
.I bndcfgu
register.
These calls will fail if the CPU or kernel does not support MPX.
Kernel support for MPX is enabled via the
@ -861,14 +869,17 @@ enabled.
All threads in a process are affected by these calls.
The child of a fork(2) will inherit the state of MPX management.
During an execve(2) call, MPX management will be reset to a state
as if PR_MPX_DISABLE_MANAGEMENT had been called.
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.
For further information on Intel MPX, see the kernel source file
.IR Documentation/x86/intel_mpx.txt .
.\"
.SH RETURN VALUE
On success,
@ -1157,12 +1168,12 @@ is not valid.
.TP
.B ENXIO
.I option
is PR_MPX_ENABLE_MANAGEMENT and the kernel was unable to enable
management. Ensure the kernel and processor have MPX support.
.TP
.B ENXIO
.I option
is PR_MPX_DISABLE_MANAGEMENT and the kernel or CPU does not support MPX.
was
.BR PR_MPX_ENABLE_MANAGEMENT
or
.BR PR_MPX_DISABLE_MANAGEMENT
and the kernel or the CPU does not support MPX management.
Check that the kernel and processor have MPX support.
.SH VERSIONS
The
.BR prctl ()