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Date: Fri, 2 Sep 2016 18:15:30 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Jiri Olsa <jolsa@kernel.org>, lkml <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>, Ingo Molnar <mingo@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened
 usercopy feature
Message-ID: <20160902161530.GB31273@krava>
References: <1472819145-27260-1-git-send-email-jolsa@kernel.org>
 <20160902151713.GM5871@two.firstfloor.org>
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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