ASLR implementation

Question

I just read about how ASLR helps in preventing buffer overflow attacks and would like to have a look at its implementation.

Could someone offer a few pointers on where I could start looking? I would also love it if you could point me towards more reading material related to the same.

Answer 1

The implementation can naturally be found in the Linux kernel source tree. Even just grepping for.. randomize_va_space will turn up enough results to start on.

In the elf loader #ifdef arch_randomize_brk -> arch_randomize_brk -> randomize_range

Answer 2

How to use?

https://lkml.org/lkml/2010/11/30/110

What is that?

http://en.wikipedia.org/wiki/Address_space_layout_randomization

Why?

To prevent 2 types of attack:

http://en.wikipedia.org/wiki/Return-to-libc_attack

http://en.wikipedia.org/wiki/Return-oriented_programming

because both attack assumed your code area if fixed in memory.