On Fri, 03 Jul 2009, Jiri Kosina wrote:
> > There a few legacy applications out there (such as some ancient
>
> ... would you please fix this typo/grammo as well? (There a few ...)
>
> > versions of libc.so.5 from 1996) that assume that brk area starts
>
> Also, the text itself doesn't seem to be super-clear ... namely, it
> describes what CONFIG_COMPAT_BRK is about, but doesn't really clarify how
> exactly does this correlate with randomize_va_space == 2. Would you mind
> also fixing this bit?
I hope I didn't misread the sources :-) Opinions?
---
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 <horst@xxxxxxxxxxxxxx>
---
Documentation/sysctl/kernel.txt | 30 +++++++++++++++++-------------
1 files changed, 17 insertions(+), 13 deletions(-)
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 322a00b..dd8322f 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -303,25 +303,29 @@ 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
- complicated.
- 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.
==============================================================
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