Re: CVS commit: src/sys

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Jun 15, 2017 at 10:51:34AM +0200, Maxime Villard wrote:
> Le 15/06/2017 à 10:28, Manuel Bouyer a écrit :
> > On Thu, Jun 15, 2017 at 10:11:21AM +0200, Maxime Villard wrote:
> > > > There were several strong objections to our change in this thread:
> > > > http://mail-index.netbsd.org/tech-kern/2017/03/28/msg021705.html
> > > 
> > > Man, that's another thread. My commit is about PMCs, not rdtsc.
> > 
> > OK I got confused.
> > then where was this change discussed ?
> 
> nowhere
> 
> > IHMO the same arguments from the thread applies here.
> 
> Which argument? fyi, pmcs are not enabled by default, and until a few months
> ago they didn't even work. I'm making them privileged with the intention of
> enabling them for real.
> 
> The reasons we need root privileges are: the msr values are given by userland
> and we don't want unprivileged users to panic the system, and more generally,
> pmcs can be used to defeat aslr (as said in the thread, btw).

So, it a user wants to use the PMCs to tune a code, I have to give him
root access. I can't see how this improves the security.

AFAIK on linux PMCs can be used without root.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--