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Message-ID: <4b028b92-81f3-362f-c5be-b7a35cedf5ee@kernel.org>
Date: Thu, 21 Jul 2016 22:34:33 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Valdis.Kletnieks@...edu, kernel-hardening@...ts.openwall.com
Cc: 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
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
View attachment "0001-x86-mm-Fix-populate_pgd.patch" of type "text/x-patch" (3464 bytes)
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