-.\" -*- nroff -*-
-.\" Copyright (C) 2007 Michael Kerrisk <mtk-manpages@gmx.net>
+.\" Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com>
.\" and Copyright (C) 1995 Michael Shields <shields@tembel.org>.
.\"
+.\" %%%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.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and author of this work.
+.\" %%%LICENSE_END
.\"
.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1997-05-31 by Andries Brouwer <aeb@cwi.nl>
.\" 2007-06-02, mtk: Fairly substantial rewrites and additions, and
.\" a much improved example program.
.\"
-.TH MPROTECT 2 2007-06-02 "Linux" "Linux Programmer's Manual"
+.TH MPROTECT 2 2019-08-02 "Linux" "Linux Programmer's Manual"
.SH NAME
-mprotect \- set protection on a region of memory
+mprotect, pkey_mprotect \- set protection on a region of memory
.SH SYNOPSIS
.nf
.B #include <sys/mman.h>
-.sp
-\fBint mprotect(const void *\fIaddr\fB, size_t \fIlen\fB, int \fIprot\fB);
+.PP
+.BI "int mprotect(void *" addr ", size_t " len ", int " prot );
+
+.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
+.B #include <sys/mman.h>
+.PP
+.BI "int pkey_mprotect(void *" addr ", size_t " len ", int " prot ", int " pkey ");
.fi
.SH DESCRIPTION
.BR mprotect ()
-changes protection for the calling process's memory page(s)
+changes the access protections for the calling process's memory pages
containing any part of the address range in the
interval [\fIaddr\fP,\ \fIaddr\fP+\fIlen\fP\-1].
.I addr
must be aligned to a page boundary.
-
+.PP
If the calling process tries to access memory in a manner
-that violates the protection, then the kernel generates a
+that violates the protections, then the kernel generates a
.B SIGSEGV
signal for the process.
.PP
.I prot
-is either
+is a combination of the following access flags:
.B PROT_NONE
or a bitwise-or of the other values in the following list:
.TP 1.1i
.TP
.B PROT_EXEC
The memory can be executed.
-.\" FIXME
-.\" Document PROT_GROWSUP and PROT_GROWSDOWN
-.SH "RETURN VALUE"
+.TP
+.BR PROT_SEM " (since Linux 2.5.7)"
+The memory can be used for atomic operations.
+This flag was introduced as part of the
+.BR futex (2)
+implementation (in order to guarantee the ability to perform atomic
+operations required by commands such as
+.BR FUTEX_WAIT ),
+but is not currently used in on any architecture.
+.TP
+.BR PROT_SAO " (since Linux 2.6.26)"
+.\" commit aba46c5027cb59d98052231b36efcbbde9c77a1d
+.\" commit ef3d3246a0d06be622867d21af25f997aeeb105f
+The memory should have strong access ordering.
+This feature is specific to
+the PowerPC architecture
+(version 2.06 of the architecture specification adds the SAO CPU feature,
+and it is available on POWER 7 or PowerPC A2, for example).
+.PP
+Additionally (since Linux 2.6.0),
+.I prot
+can have one of the following flags set:
+.TP 1.1i
+.\" mm/mmap.c:
+.\" vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
+.\" mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
+.\" And calc_vm_flag_bits converts only GROWSDOWN/DENYWRITE/LOCKED.
+.B PROT_GROWSUP
+Apply the protection mode up to the end of a mapping
+that grows upwards.
+(Such mappings are created for the stack area on
+architectures\(emfor example, HP-PARISC\(emthat
+have an upwardly growing stack.)
+.\" The VMA is one that was marked with VM_GROWSUP by the kernel
+.\" when the stack was created. Note that (unlike VM_GROWSDOWN),
+.\" there is no mmap() flag (analogous to MAP_GROWSDOWN) for
+.\" creating a VMA that is marked VM_GROWSUP.
+.TP
+.B PROT_GROWSDOWN
+Apply the protection mode down to the beginning of a mapping
+that grows downward
+(which should be a stack segment or a segment mapped with the
+.B MAP_GROWSDOWN
+flag set).
+.PP
+Like
+.BR mprotect (),
+.BR pkey_mprotect ()
+changes the protection on the pages specified by
+.IR addr
+and
+.IR len .
+The
+.I pkey
+argument specifies the protection key (see
+.BR pkeys (7))
+to assign to the memory.
+The protection key must be allocated with
+.BR pkey_alloc (2)
+before it is passed to
+.BR pkey_mprotect ().
+For an example of the use of this system call, see
+.BR pkeys (7).
+.SH RETURN VALUE
On success,
.BR mprotect ()
-returns zero.
-On error, \-1 is returned, and
+and
+.BR pkey_mprotect ()
+return zero.
+On error, these system calls return \-1, and
.I errno
is set appropriately.
.SH ERRORS
to mark it
.BR PROT_WRITE .
.TP
-.B EFAULT
-The memory cannot be accessed.
-.TP
.B EINVAL
\fIaddr\fP is not a valid pointer,
or not a multiple of the system page size.
-.\" Or: both PROT_GROWSUP and PROT_GROWSDOWN were specified in 'prot'.
+.TP
+.BR EINVAL
+.RB ( pkey_mprotect ())
+\fIpkey\fP has not been allocated with
+.BR pkey_alloc (2)
+.TP
+.BR EINVAL
+Both
+.BR PROT_GROWSUP
+and
+.BR PROT_GROWSDOWN
+were specified in
+.IR prot .
+.TP
+.BR EINVAL
+Invalid flags specified in
+.IR prot .
+.TP
+.BR EINVAL
+(PowerPC architecture)
+.B PROT_SAO
+was specified in
+.IR prot ,
+but SAO hardware feature is not available.
.TP
.B ENOMEM
Internal kernel structures could not be allocated.
-Or: addresses in the range
+.TP
+.B ENOMEM
+Addresses in the range
.RI [ addr ,
-.IR addr + len ]
+.IR addr + len \-1]
are invalid for the address space of the process,
or specify one or more pages that are not mapped.
-.SH "CONFORMING TO"
-SVr4, POSIX.1-2001.
+(Before kernel 2.4.19, the error
+.BR EFAULT
+was incorrectly produced for these cases.)
+.TP
+.B ENOMEM
+Changing the protection of a memory region would result in the total number of
+mappings with distinct attributes (e.g., read versus read/write protection)
+exceeding the allowed maximum.
+.\" I.e., the number of VMAs would exceed the 64 kB maximum
+(For example, making the protection of a range
+.BR PROT_READ
+in the middle of a region currently protected as
+.BR PROT_READ|PROT_WRITE
+would result in three mappings:
+two read/write mappings at each end and a read-only mapping in the middle.)
+.SH VERSIONS
+.BR pkey_mprotect ()
+first appeared in Linux 4.9;
+library support was added in glibc 2.27.
+.SH CONFORMING TO
+.BR mprotect ():
+POSIX.1-2001, POSIX.1-2008, SVr4.
.\" SVr4 defines an additional error
.\" code EAGAIN. The SVr4 error conditions don't map neatly onto Linux's.
POSIX says that the behavior of
is unspecified if it is applied to a region of memory that
was not obtained via
.BR mmap (2).
+.PP
+.BR pkey_mprotect ()
+is a nonportable Linux extension.
.SH NOTES
-On Linux it is always legal to call
+On Linux, it is always permissible to call
.BR mprotect ()
on any address in a process's address space (except for the
kernel vsyscall area).
-In particular it can be used
+In particular, it can be used
to change existing code mappings to be writable.
-
+.PP
Whether
.B PROT_EXEC
has any effect different from
.B PROT_READ
-is architecture and kernel version dependent.
-On some hardware architectures (e.g., x86),
-.BR PROT_WRITE
+depends on processor architecture, kernel version, and process state.
+If
+.B READ_IMPLIES_EXEC
+is set in the process's personality flags (see
+.BR personality (2)),
+specifying
+.B PROT_READ
+will implicitly add
+.BR PROT_EXEC .
+.PP
+On some hardware architectures (e.g., i386),
+.B PROT_WRITE
implies
.BR PROT_READ .
-
-POSIX.1-2001 says that an implementation may permit access
+.PP
+POSIX.1 says that an implementation may permit access
other than that specified in
.IR prot ,
-but at a minimum can only allow write access if
+but at a minimum can allow write access only if
.B PROT_WRITE
has been set, and must not allow any access if
.B PROT_NONE
has been set.
+.PP
+Applications should be careful when mixing use of
+.BR mprotect ()
+and
+.BR pkey_mprotect ().
+On x86, when
+.BR mprotect ()
+is used with
+.IR prot
+set to
+.B PROT_EXEC
+a pkey is may be allocated and set on the memory implicitly
+by the kernel, but only when the pkey was 0 previously.
+.PP
+On systems that do not support protection keys in hardware,
+.BR pkey_mprotect ()
+may still be used, but
+.IR pkey
+must be set to -1.
+When called this way, the operation of
+.BR pkey_mprotect ()
+is equivalent to
+.BR mprotect ().
.SH EXAMPLE
.\" sigaction.2 refers to this example
.PP
-The program below allocates four pages of memory, makes the third
-of these pages read-only, and then executes a loop that walks upwards
+The program below demonstrates the use of
+.BR mprotect ().
+The program allocates four pages of memory, makes the third
+of these pages read-only, and then executes a loop that walks upward
through the allocated region modifying bytes.
-
+.PP
An example of what we might see when running the program is the
following:
-
-.in +0.5i
-.nf
-$ ./a.out
+.PP
+.in +4n
+.EX
+.RB "$" " ./a.out"
Start of region: 0x804c000
Got SIGSEGV at address: 0x804e000
-.fi
+.EE
.in
-.nf
-
+.SS Program source
+\&
+.EX
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <errno.h>
#include <sys/mman.h>
-#define die(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0)
+#define handle_error(msg) \e
+ do { perror(msg); exit(EXIT_FAILURE); } while (0)
-char *buffer;
+static char *buffer;
static void
handler(int sig, siginfo_t *si, void *unused)
{
- printf("Got SIGSEGV at address: 0x%lx\\n",
+ /* Note: calling printf() from a signal handler is not safe
+ (and should not be done in production programs), since
+ printf() is not async\-signal\-safe; see signal-safety(7).
+ Nevertheless, we use printf() here as a simple way of
+ showing that the handler was called. */
+
+ printf("Got SIGSEGV at address: 0x%lx\en",
(long) si\->si_addr);
exit(EXIT_FAILURE);
}
sigemptyset(&sa.sa_mask);
sa.sa_sigaction = handler;
if (sigaction(SIGSEGV, &sa, NULL) == \-1)
- die("sigaction");
+ handle_error("sigaction");
pagesize = sysconf(_SC_PAGE_SIZE);
if (pagesize == \-1)
- die("sysconf");
+ handle_error("sysconf");
/* Allocate a buffer aligned on a page boundary;
initial protection is PROT_READ | PROT_WRITE */
buffer = memalign(pagesize, 4 * pagesize);
if (buffer == NULL)
- die("memalign");
+ handle_error("memalign");
- printf("Start of region: 0x%lx\\n", (long) buffer);
+ printf("Start of region: 0x%lx\en", (long) buffer);
if (mprotect(buffer + pagesize * 2, pagesize,
- PROT_NONE) == \-1)
- die("mprotect");
+ PROT_READ) == \-1)
+ handle_error("mprotect");
for (p = buffer ; ; )
- *(p++) = 'a';
+ *(p++) = \(aqa\(aq;
- printf("Loop completed\\n"); /* Should never happen */
+ printf("Loop completed\en"); /* Should never happen */
exit(EXIT_SUCCESS);
}
-.fi
-.SH "SEE ALSO"
+.EE
+.SH SEE ALSO
.BR mmap (2),
-.BR sysconf (3)
+.BR sysconf (3),
+.BR pkeys (7)
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