linux-kernel - Re: [PATCH] irqchip/gic: prevent buffer overflow in gic_ipi_send

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Message-ID: <b7d701e1-3cdd-3490-2ee1-70d96fa22703@omp.ru>
Date: Fri, 6 Sep 2024 23:36:46 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Marc Zyngier <maz@...nel.org>, Thomas Gleixner <tglx@...utronix.de>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] irqchip/gic: prevent buffer overflow in
 gic_ipi_send_mask()

On 9/6/24 11:29 PM, Sergey Shtylyov wrote:
[...]

>>>> ARM GIC arch v2 spec claims support for just 8 CPU interfaces.  However,
>>>> looking at the GIC driver's irq_set_affinity() method, it seems that the
>>>> passed CPU mask may contain the logical CPU #s beyond 8, and that method
>>>> filters them out before reading gic_cpu_map[], bailing out with
>>>> -EINVAL.
>>>
>>> The reasoning is correct in theory, but in reality it's a non problem.
>>>
>>> Simply because processors which use this GIC version cannot have more
>>> than 8 cores.
>>>
>>> That means num_possible_cpus() <= 8 so the cpumask handed in cannot have
>>> bits >= 8 set. Ergo for_each_cpu() can't return a bit which is >= 8.

[...]

>> 33de0aa4bae98, the affinity that the driver gets is narrowed to what
>> is actually *online*.
> 
>    What I haven't quite understood from my (cursory) looking at the GICv2
> spec (and the GIC driver) is why only one CPU (with a lowest #) is selected
> from *mask_val before writing to GICD_GIC_DIST_TARGET, while the spec holds

   Sorry, meant to type GIC_DIST_TARGET (or GICD_ITARGETSRn, as the spec
calls it)...

[...]

>> Thanks,
>>
>> 	M.

MBR, Sergey