From: Eric Wong <normalperson@...>
Date: 2012-03-24T10:46:31+09:00
Subject: Re: Write to kernel buffer?

ruby rub <lists@ruby-forum.com> wrote:
> It takes the password as input from the user, holds it in memory for
> some period of time, and then overwrites it. It also doesn't
> echo when the password is typed in. This is great but I also want to
> make sure the password is overwritten in the kernel buffer. Does anyone
> have any suggestions? Really I would just like to be pointed in the
> right direction :).

I don't think there's a good way to force this from userspace (in any
programming language).

Kernels will zero any memory it gives to userspace (via brk(2)/mmap(2)),
but kernels will internally reuse buffers any way it sees fit.  Even if
you could clear the kernel memory right away (via custom kernel
module/syscall), you can't guarantee hardware buffers
(keyboard/network/console/video card/etc...) are cleared.