Re: Hashed pointer issues

From: Steven Rostedt
Date: Mon Apr 30 2018 - 12:41:43 EST

On Mon, 30 Apr 2018 16:31:52 +0000
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Mon, Apr 30, 2018 at 9:11 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > I (or other folks?) had proposed this before, but, AIUI, Linus remains
> > opposed.
> Yeah, I hate this, because it will make people paper over their problems by
> just booting with that option.
> I think it should just be fixed.
> Is there really any reason why trace buffers have to be dumped so early
> that the entropy hasn't even taken yet?

In this case, an RCU stall was triggering and a "dump on oops" would
dump the trace buffers, (before entropy was established).

> And if we really want a command line option, can we make that still hash
> the pointer, just force the entropy early. That way kernel developers that
> test that command line option are still testing the *hashing*, they just
> are missing the good entropy.

That may work too. Even with bad entropy, pointers at start up are hard
to come by, and I can't see a hacker being able to use them as it only
happens once during boot.

-- Steve