linux-kernel - Re: [PATCHv2 1/4] x86/mm/ident_map: Fix virtual address wrap to zero

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Message-ID: <87wmkim4sy.ffs@tglx>
Date: Thu, 15 Aug 2024 12:57:49 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: 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>, "Rafael J. Wysocki" <rafael@...nel.org>, Andy Lutomirski
 <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Baoquan He
 <bhe@...hat.com>, Ard Biesheuvel <ardb@...nel.org>, Tom Lendacky
 <thomas.lendacky@....com>, Andrew Morton <akpm@...ux-foundation.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, Sean Christopherson
 <seanjc@...gle.com>, linux-kernel@...r.kernel.org,
 linux-acpi@...r.kernel.org, Kai Huang <kai.huang@...el.com>
Subject: Re: [PATCHv2 1/4] x86/mm/ident_map: Fix virtual address wrap to zero

On Thu, Aug 15 2024 at 12:15, Kirill A. Shutemov wrote:
> On Wed, Aug 14, 2024 at 09:25:35PM +0200, Thomas Gleixner wrote:
>> On Wed, Aug 14 2024 at 15:46, Kirill A. Shutemov wrote:
>> > Calculation of 'next' virtual address doesn't protect against wrapping
>> > to zero. It can result in page table corruption and hang. The
>> > problematic case is possible if user sets high x86_mapping_info::offset.
>> 
>> So this should have a Fixes tag, right?
>
> Well, I guess we can add
>
> Fixes: e4630fdd4763 ("x86/power/64: Always create temporary identity mapping correctly")
>
> but the bug is not triggirable with current upstream code.
>
> It only wraps to zero if you touch top PGD entry. There's no such users in
> upstream. Only hibernate_64.c uses x86_mapping_info::offset and it works
> on direct mapping range which is not top PGD entry.

Fair enough, but please mention that in the change log.