From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [kernel-hardening] [PATCH v5 03/32] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated Date: Fri, 22 Jul 2016 12:21:05 +0200 Message-ID: <20160722102105.GA20771@gmail.com> References: <5741.1469162592@turing-police.cc.vt.edu> <4b028b92-81f3-362f-c5be-b7a35cedf5ee@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-wm0-f67.google.com ([74.125.82.67]:34927 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753287AbcGVKVN (ORCPT ); Fri, 22 Jul 2016 06:21:13 -0400 Content-Disposition: inline In-Reply-To: <4b028b92-81f3-362f-c5be-b7a35cedf5ee@kernel.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Andy Lutomirski Cc: Valdis.Kletnieks@vt.edu, kernel-hardening@lists.openwall.com, x86@kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Borislav Petkov , Nadav Amit , Kees Cook , Brian Gerst , Linus Torvalds , Josh Poimboeuf , Jann Horn , Heiko Carstens * Andy Lutomirski wrote: > On 07/21/2016 09:43 PM, Valdis.Kletnieks@vt.edu wrote: > >On Mon, 11 Jul 2016 13:53:36 -0700, Andy Lutomirski said: > >>This avoids pointless races in which another CPU or task might see = a > >>partially populated global pgd entry. These races should normally > >>be harmless, but, if another CPU propagates the entry via > >>vmalloc_fault and then populate_pgd fails (due to memory allocation > >>failure, for example), this prevents a use-after-free of the pgd > >>entry. > >> > >>Signed-off-by: Andy Lutomirski > >>--- > >> arch/x86/mm/pageattr.c | 9 ++++++--- > >> 1 file changed, 6 insertions(+), 3 deletions(-) > > > >I just bisected a failure to boot down to this patch. On my Dell La= titude > >laptop, it results in the kernel being loaded and then just basicall= y sitting > >there dead in the water - as far as I can tell, it dies before the k= ernel > >ever gets going far enough to do any console I/O (even with ignore_l= oglevel). > >Nothing in /sys/fs/pstore either. I admit not understanding the VM = code > >at all, so I don't have a clue *why* this causes indigestion... > > > >CPU is an Intel Core i5-3340M in case that matters.... > > >=20 > How much memory do you have and what's your config? My code is obvio= usly > buggy, but I'm wondering why neither I nor the 0day bot caught this. >=20 > The attached patch is compile-tested only. (Even Thunderbird doesn't= want > to send non-flowed text right now, sigh.) >=20 > --Andy > From 6589ddf69a1369e1ecb95f0af489d90b980e256e Mon Sep 17 00:00:00 200= 1 > Message-Id: <6589ddf69a1369e1ecb95f0af489d90b980e256e.1469165371.git.= luto@kernel.org> > From: Andy Lutomirski > Date: Thu, 21 Jul 2016 22:22:02 -0700 > Subject: [PATCH] x86/mm: Fix populate_pgd() >=20 > I make an obvious error in populate_pgd() -- it would fail to correct= ly > populate the page tables when it allocated a new pud page. JFYI, on allnoconfig it gives: arch/x86/mm/pageattr.c:1016:20: error: implicit declaration of functi= on =E2=80=98pud_index=E2=80=99 [-Werror=3Dimplicit-function-declaration= ] Thanks, Ingo