Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened usercopy feature

[Jiri Olsa]

On Fri, Sep 02, 2016 at 08:17:13AM -0700, Andi Kleen wrote:
> On Fri, Sep 02, 2016 at 02:25:45PM +0200, Jiri Olsa wrote:
> > One of the bullets for hardened usercopy feature is:
> >   - object must not overlap with kernel text
> > 
> > which is what we expose via /proc/kcore. We can hit
> > this check and crash the system very easily just by
> > reading the text area in kcore file:
> > 
> >   usercopy: kernel memory exposure attempt detected from ffffffff8179a01f (<kernel text>) (4065 bytes)
> >   kernel BUG at mm/usercopy.c:75!
> > 
> > Omitting kernel text area from kcore when there's
> > hardened usercopy feature is enabled.
> 
> That will completely break PT decoding, which relies on looking
> at the kernel text in /proc/kcore.
> 
> Need a different fix here, perhaps some special copy function
> that is not hardened.

ok, I'll try to come up with something

thanks,
jirka