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| -rw-r--r-- | 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 2dbff53369d0..3e5b63ebb821 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -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 - 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. ============================================================== |