|author||Horst Schirmeier <email@example.com>||2009-07-03 14:20:17 +0200|
|committer||Jiri Kosina <firstname.lastname@example.org>||2009-09-21 15:14:53 +0200|
trivial: doc: document missing value 2 for randomize-va-space
The documentation for /proc/sys/kernel/* does not mention the possible value 2 for randomize-va-space yet. While being there, doing some reformatting, fixing grammar problems and clarifying the correlations between randomize-va-space, kernel parameter "norandmaps" and the CONFIG_COMPAT_BRK option. Signed-off-by: Horst Schirmeier <email@example.com> Signed-off-by: Jiri Kosina <firstname.lastname@example.org>
Diffstat (limited to 'Documentation/sysctl')
1 files changed, 17 insertions, 13 deletions
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 2dbff53369d..3e5b63ebb82 100644
@@ -319,25 +319,29 @@ This option can be used to select the type of process address
space randomization that is used in the system, for architectures
that support this feature.
-0 - Turn the process address space randomization off by default.
+0 - Turn the process address space randomization off. This is the
+ default for architectures that do not support this feature anyways,
+ and kernels that are booted with the "norandmaps" parameter.
1 - Make the addresses of mmap base, stack and VDSO page randomized.
This, among other things, implies that shared libraries will be
- loaded to random addresses. Also for PIE-linked binaries, the location
- of code start is randomized.
+ loaded to random addresses. Also for PIE-linked binaries, the
+ location of code start is randomized. This is the default if the
+ CONFIG_COMPAT_BRK option is enabled.
- With heap randomization, the situation is a little bit more
- There a few legacy applications out there (such as some ancient
+2 - Additionally enable heap randomization. This is the default if
+ CONFIG_COMPAT_BRK is disabled.
+ There are a few legacy applications out there (such as some ancient
versions of libc.so.5 from 1996) that assume that brk area starts
- just after the end of the code+bss. These applications break when
- start of the brk area is randomized. There are however no known
+ just after the end of the code+bss. These applications break when
+ start of the brk area is randomized. There are however no known
non-legacy applications that would be broken this way, so for most
- systems it is safe to choose full randomization. However there is
- a CONFIG_COMPAT_BRK option for systems with ancient and/or broken
- binaries, that makes heap non-randomized, but keeps all other
- parts of process address space randomized if randomize_va_space
- sysctl is turned on.
+ systems it is safe to choose full randomization.
+ Systems with ancient and/or broken binaries should be configured
+ with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
+ address space randomization.