[Cerowrt-devel] KASLR: Do we have to worry about other arches than x86?

[Dave Taht <dave.taht@gmail.com>]

or is this primarily a virtualization bug?

http://hn.premii.com/#/article/16046636

"Bad news: the software mitigation is expensive

The primary reason for the old Linux behaviour of mapping kernel
memory in the same page tables as user memory is so that when the
user’s code triggers a system call, fault, or an interrupt fires, it
is not necessary to change the virtual memory layout of the running
process.

Since it is unnecessary to change the virtual memory layout, it is
further unnecessary to flush highly performance-sensitive CPU caches
that are dependant on that layout, primarily the Translation Lookaside
Buffer.

With the page table splitting patches merged, it becomes necessary for
the kernel to flush these caches every time the kernel begins
executing, and every time user code resumes executing. For some
workloads, the effective total loss of the TLB lead around every
system call leads to highly visible slowdowns: @grsecurity measured a
simple case where Linux “du -s” suffered a 50% slowdown on a recent
AMD CPU."

-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619