Re: [PATCH] ACPI: PPTT: Fix processor subtable walk

[Sudeep Holla <sudeep.holla@arm.com>]

On Wed, May 07, 2025 at 09:30:25PM -0500, Jeremy Linton wrote:
> The original PPTT code had a bug where the processor subtable length
> was not correctly validated when encountering a truncated
> acpi_pptt_processor node.
> 
> Commit 7ab4f0e37a0f4 ("ACPI PPTT: Fix coding mistakes in a couple of
> sizeof() calls") attempted to fix this by validating the size is as
> large as the acpi_pptt_processor node structure. This introduced a
> regression where the last processor node in the PPTT table is ignored
> if it doesn't contain any private resources. That results errors like:
> 
>   ACPI PPTT: PPTT table found, but unable to locate core XX (XX)
>   ACPI: SPE must be homogeneous
> 
> Furthermore, it fail in a common case where the node length isn't
> equal to the acpi_pptt_processor structure size, leaving the original
> bug in a modified form.
> 
> Correct the regression by adjusting the loop termination conditions as
> suggested by the bug reporters. An additional check performed after
> the subtable node type is detected, validates the acpi_pptt_processor
> node is fully contained in the PPTT table. Repeating the check in
> acpi_pptt_leaf_node() is largely redundant as the node is already
> known to be fully contained in the table.
> 
> The case where a final truncated node's parent property is accepted,
> but the node itself is rejected should not be considered a bug.
> 

Thanks for picking this up and describing the issue properly in the commit
message.

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>

-- 
Regards,
Sudeep