linux-kernel - Re: [PATCH 4.4 00/37] 4.4.110-stable review

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Date:   Thu, 11 Jan 2018 15:18:43 -0500
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Voegtle <tv@...96.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Shuah Khan <shuahkh@....samsung.com>, patches@...nelci.org,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        lkft-triage@...ts.linaro.org, stable <stable@...r.kernel.org>,
        Steve Sistare <steven.sistare@...cle.com>
Subject: Re: [PATCH 4.4 00/37] 4.4.110-stable review



On 01/11/2018 03:10 PM, Greg Kroah-Hartman wrote:
> On Thu, Jan 11, 2018 at 01:36:50PM -0500, Pavel Tatashin wrote:
>> I have root caused the memory corruption panics/hangs that I've been
>> experiencing during boot with the latest 4.4.110 kernel. The problem
>> as was suspected by Andy Lutomirski is with interaction between PTI
>> and EFI. It may affect any system that has EFI bios.  I have not
>> verified if it can affect any other kernel beside 4.4.110
>>
>> Attached is the fix for this issue with explanations that Steve
>> Sistare and I developed.
> 
> Nice, but why does this not show up in 4.9 and 4.14 and Linus's tree as
> well on this hardware?  Nor on the SLES12 SP3 kernel?
> 
> What is different there that 4.4 requires?  That worries me more than
> your fix (which looks good to me, fwiw.)

Hi Greg,

I have not studied other versions of kernels, efi was changed 
substantially since 4.4. But, even on 4.4.110 there are several things 
have to happen for this bug to show-up:

1. During boot memmblock must allocate address that is not 2PAGE_SIZE 
aligned.
2. nmi must arrive exactly when EFI replaced page table.

While I was debugging this problem, I tried to enable, kasan, vm_debug, 
add more printfs etc, but every little change would cause this problem 
to disappear, or appear less frequently.

Thank you,
Pavel