Date: Fri, 22 Jul 2016 12:21:05 +0200 From: Ingo Molnar <mingo@...nel.org> To: Andy Lutomirski <luto@...nel.org> Cc: Valdis.Kletnieks@...edu, kernel-hardening@...ts.openwall.com, x86@...nel.org, linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, Borislav Petkov <bp@...en8.de>, Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jann@...jh.net>, Heiko Carstens <heiko.carstens@...ibm.com> Subject: Re: [PATCH v5 03/32] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated * Andy Lutomirski <luto@...nel.org> wrote: > On 07/21/2016 09:43 PM, Valdis.Kletnieks@...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 <luto@...nel.org> > >>--- > >> 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 Latitude > >laptop, it results in the kernel being loaded and then just basically sitting > >there dead in the water - as far as I can tell, it dies before the kernel > >ever gets going far enough to do any console I/O (even with ignore_loglevel). > >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.... > > > > How much memory do you have and what's your config? My code is obviously > buggy, but I'm wondering why neither I nor the 0day bot caught this. > > The attached patch is compile-tested only. (Even Thunderbird doesn't want > to send non-flowed text right now, sigh.) > > --Andy > From 6589ddf69a1369e1ecb95f0af489d90b980e256e Mon Sep 17 00:00:00 2001 > Message-Id: <6589ddf69a1369e1ecb95f0af489d90b980e256e.1469165371.git.luto@...nel.org> > From: Andy Lutomirski <luto@...nel.org> > Date: Thu, 21 Jul 2016 22:22:02 -0700 > Subject: [PATCH] x86/mm: Fix populate_pgd() > > I make an obvious error in populate_pgd() -- it would fail to correctly > 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 function ‘pud_index’ [-Werror=implicit-function-declaration] Thanks, Ingo
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