Date: Fri, 22 Jul 2016 11:31:15 -0700 From: Andy Lutomirski <luto@...capital.net> To: Ingo Molnar <mingo@...nel.org> Cc: Andy Lutomirski <luto@...nel.org>, Valdis Kletnieks <Valdis.Kletnieks@...edu>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, X86 ML <x86@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-arch <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 On Fri, Jul 22, 2016 at 11:21 AM, Andy Lutomirski <luto@...capital.net> wrote: > On Fri, Jul 22, 2016 at 3:21 AM, Ingo Molnar <mingo@...nel.org> wrote: >> >> * 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] > > As it happens, my fix interacts badly with the steaming pile of crap > that is Linux's support for <4 page table levels. Can you just revert > the offending patch and I'll redo it differently? No, don't revert it. The result doesn't work. I'll send something.
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