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Comment by agumonkey | Hacker News Reader

is linux randomizing is per exec ?

ps: BSD have started to randomize at boot time, fun times

> is linux randomizing is per exec ?

Not entirely sure what you're meaning to ask, but yes, Linux does KASLR and tries very hard not to leak pointer addresses from the running kernel to unprivileged userspace:

https://lwn.net/Articles/569635/

It's been enabled by default since the upstream 4.12 kernel, and usually well before that in distros.

KALSR's not the same as ASLR (although ideologically related). ALSR has been around for a good number of years in userspace via randomize_va_space sysctl

(edit I presume that's what the poster above mentioned re: per exec)

yes ALSR, sorry, acronym fail on my part. So ALSR does randomize bindings on each execution ?

Yes. If I run e.g. `ldd /bin/bash` multiple times, it shows different memory addresses each time. That's ASLR.

I never bothered to check, what a m... I am. Thanks a lot :)

Also worth mentioning that `ldd` only demonstrates how shared libraries are mmap'ed at randomized locations. Stack and heap allocations are also randomized at execution time.

cat /proc/self/maps is a better way to see that. If it's built with PIE, the executable base is randomized. Some distributions use full ASLR across the board (Alpine, Android, ChromeOS, Hardened Gentoo) while others don't yet enable PIE globally or have only recently started and it isn't all pushed out yet (OpenSUSE, Fedora, Debian).

Linux randomises userspace executables on per-exec (check out /proc/self/maps).

BSD also does the same for userspace, but their new feature is that they randomise the kernel per-boot (by re-linking the objects). This is a far stronger form of kASLR (though I think they're calling it something else because it requires relinking the kernel binary).

Even Windows does this well.

Bragging about boot-time ASLR seems quite odd for an article like this, given that traditional operating systems have had similar (and in many ways superior) features like this for more than a decade (PaX introduced ASLR in Linux in 2001, OpenBSD had it by-default in 2003, and Linux shipped it by-default in 2005).

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