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

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Message-ID: <86o752v8xs.wl-maz@kernel.org>
Date: Thu, 05 Sep 2024 08:47:11 +0100
From: Marc Zyngier <maz@...nel.org>
To: Sergey Shtylyov <s.shtylyov@....ru>, 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 Thu, 05 Sep 2024 08:29:32 +0100,
Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> On Wed, Sep 04 2024 at 23:23, 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.

That.

The irq_set_affinity() check exists because the affinity can be
provided by userspace, and used to be be *anything*. Since
33de0aa4bae98, the affinity that the driver gets is narrowed to what
is actually *online*.

So we could actually relax the check in the driver (not that it really
matters).

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.