linux-kernel - Re: [PATCH v3] x86/e820: Fix handling of subpage regions when calculating nosave ranges

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <78346ff0-d5ee-48f0-ac4d-762a5ec18eb7@qtmlabs.xyz>
Date: Mon, 7 Apr 2025 07:53:42 +0700
From: Myrrh Periwinkle <myrrhperiwinkle@...labs.xyz>
To: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org,
 Roberto Ricci <io@...icci.it>
Subject: Re: [PATCH v3] x86/e820: Fix handling of subpage regions when
 calculating nosave ranges

On 4/7/25 01:36, Ingo Molnar wrote:

> * Ingo Molnar<mingo@...nel.org> wrote:
>
>> * Myrrh Periwinkle<myrrhperiwinkle@...labs.xyz> wrote:
>>
>>> The current implementation of e820__register_nosave_regions suffers from
>>> multiple serious issues:
>>>   - The end of last region is tracked by PFN, causing it to find holes
>>>     that aren't there if two consecutive subpage regions are present
>>>   - The nosave PFN ranges derived from holes are rounded out (instead of
>>>     rounded in) which makes it inconsistent with how explicitly reserved
>>>     regions are handled
>>>
>>> Fix this by:
>>>   - Treating reserved regions as if they were holes, to ensure consistent
>>>     handling (rounding out nosave PFN ranges is more correct as the
>>>     kernel does not use partial pages)
>>>   - Tracking the end of the last RAM region by address instead of pages
>>>     to detect holes more precisely
>>>
>>> Cc:stable@...r.kernel.org
>>> Fixes: e5540f875404 ("x86/boot/e820: Consolidate 'struct e820_entry *entry' local variable names")
>> So why is this SHA1 indicated as the root cause? AFAICS that commit
>> does nothing but cleanups, so it cannot cause such regressions.
> BTW.:
>
>   A) "It was the first random commit that seemed related, sry"
>   B) "It's a 15 years old bug, but I wanted to indicate a fresh, 8-year old bug to get this into -stable. Busted!"

You got me :) How did you know that this is a 15 years old bug? 
(although I didn't think the age of the bug a patch fixes would affect 
its chances of getting to -stable)

This specific revision was picked since it's the latest one that this 
patch can be straightforwardly applied to (there is a (trivial) merge 
conflict with -stable, though).

Later, I managed to track the buggy logic back to 1c10070a55a3 ("i386: 
do not restore reserved memory after hibernation"), which I believe is 
the very first occurrence of this bug. If you prefer, I can send a v4 
with a more correct Fixes: tag (or feel free to do so yourself when 
applying this patch).

> ... are perfectly fine answers in my book. :-)
>
> I'm glad about the fixes, I'm just curious how the Fixes tag came about.
>
> Thanks,
>
> 	Ingo

Regards,

Myrrh