On Mon, Aug 24, 2015 at 05:15:22PM +0300, Andrey Ryabinin wrote:

Yes, ~130Mb (3G/1G split) should work. 512Mb shadow is optional.
The only advantage of 512Mb shadow is better handling of user memory
accesses bugs
(access to user memory without copy_from_user/copy_to_user/strlen_user etc API).

No need for that to be handed by KASan.  I have patches in linux-next,
now acked by Will, which prevent the kernel accessing userspace with
zero memory footprint.  No need for remapping, we have a way to quickly
turn off access to userspace mapped pages on non-LPAE 32-bit CPUs.
(LPAE is not supported yet - Catalin will be working on that using the
hooks I'm providing once he returns.)

This isn't a debugging thing, it's a security hardening thing.  Some
use-after-free bugs are potentially exploitable from userspace.  See
the recent blackhat conference paper.

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.