Re: [PATCH v9 12/19] arm64: acpi: Harden get_cpu_for_acpi_id() against missing CPU entry

[Gavin Shan]

On 5/1/24 00:24, Jonathan Cameron wrote:
> In a review discussion of the changes to support vCPU hotplug where
> a check was added on the GICC being enabled if was was online, it was
                                                 ^^^^^^^

                                                 typo

> noted that there is need to map back to the cpu and use that to index
> into a cpumask. As such, a valid ID is needed.
>
> If an MPIDR check fails in acpi_map_gic_cpu_interface() it is possible
> for the entry in cpu_madt_gicc[cpu] == NULL.  This function would
> then cause a NULL pointer dereference.   Whilst a path to trigger
> this has not been established, harden this caller against the
> possibility.
>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> ---
> v9: New patch in response to a question from Marc Zyngier.
>      Taking the easy way out - harden against a possible condition rather
>      than establishing it never happens!
> ---
>   arch/arm64/include/asm/acpi.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)

With the typo corrected:

Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>

> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
> index bc9a6656fc0c..a407f9cd549e 100644
> --- a/arch/arm64/include/asm/acpi.h
> +++ b/arch/arm64/include/asm/acpi.h
> @@ -124,7 +124,8 @@ static inline int get_cpu_for_acpi_id(u32 uid)
>   	int cpu;
>   
>   	for (cpu = 0; cpu < nr_cpu_ids; cpu++)
> -		if (uid == get_acpi_id_for_cpu(cpu))
> +		if (acpi_cpu_get_madt_gicc(cpu) &&
> +		    uid == get_acpi_id_for_cpu(cpu))
>   			return cpu;
>   
>   	return -EINVAL;