From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754398AbcIBPRR (ORCPT ); Fri, 2 Sep 2016 11:17:17 -0400 Received: from one.firstfloor.org ([193.170.194.197]:41940 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753904AbcIBPRQ (ORCPT ); Fri, 2 Sep 2016 11:17:16 -0400 Date: Fri, 2 Sep 2016 08:17:13 -0700 From: Andi Kleen To: Jiri Olsa Cc: lkml , Kees Cook , Ingo Molnar , Adrian Hunter , Andi Kleen , KAMEZAWA Hiroyuki , Linus Torvalds Subject: Re: [PATCH] fs/proc/kcore.c: Omit kernel text area for hardened usercopy feature Message-ID: <20160902151713.GM5871@two.firstfloor.org> References: <1472819145-27260-1-git-send-email-jolsa@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1472819145-27260-1-git-send-email-jolsa@kernel.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 () (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. -Andi