Messages in this thread | | | Subject | Re: When was ASLR introduced in the Linux kernel? | From | Eric Dumazet <> | Date | Tue, 30 Nov 2010 13:15:24 +0100 |
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Le mardi 30 novembre 2010 à 12:47 +0100, Victor van der Veen a écrit : > Hi, > > - When was ASLR introduced in the Linux kernel (not PaX/ExecShield)? > - When was ASLR enabled by default? > - What's the current state of ASLR in the Linux kernel? Is it still > under development? Or should we rely on the PaX/ExecShield patches? > > Wikipedia states that "a weak form of ASLR exists in the linux kernel > since version 2.6.12 (June 2005)", but I could not find any proof that > backs this up. I grepped changelogs of the entire 2.6 kernel, but I was > unable to find any relevant information. Grepping the source code did > not help either. Any more Google results all quote the same wikipedia > line. >
randomize-va-space:
echo val >/proc/sys/kernel/randomize_va_space
vi +391 Documentation/sysctl/kernel.txt
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. 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. This is the default if the CONFIG_COMPAT_BRK option is enabled.
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 non-legacy applications that would be broken this way, so for most 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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