linux-kernel - Re: [PATCH] ACPI/PPTT: fix off-by-one error

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Message-ID: <35895e57-bbe2-4ff9-b1d4-4b70e28ed8a1@arm.com>
Date: Tue, 6 May 2025 15:11:20 -0500
From: Jeremy Linton <jeremy.linton@....com>
To: Sudeep Holla <sudeep.holla@....com>, "Heyne, Maximilian"
 <mheyne@...zon.de>
Cc: "stable@...r.kernel.org" <stable@...r.kernel.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Ard Biesheuvel <ardb@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
 "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI/PPTT: fix off-by-one error

Hi,

On 5/6/25 8:43 AM, Sudeep Holla wrote:
> On Tue, May 06, 2025 at 01:13:02PM +0000, Heyne, Maximilian wrote:
>> Commit 7ab4f0e37a0f ("ACPI PPTT: Fix coding mistakes in a couple of
>> sizeof() calls") corrects the processer entry size but unmasked a longer
>> standing bug where the last entry in the structure can get skipped due
>> to an off-by-one mistake if the last entry ends exactly at the end of
>> the ACPI subtable.
>>
> 
> Unless the firmware has populated an incorrect value for the header length, I
> don't see how this is possible. The table_end should point to the address
> immediately following the last byte of the table. None of the headers are only
> one byte long, so what am I missing that could explain this apparent
> off-by-one issue?.

More likely its because the sizeof() fix was merged without proper 
review and is wrong because the type isn't actually known on the object 
until the header is checked.