linux-kernel - Re: [PATCH v5 02/40] x86/resctrl: Add a helper to avoid reaching into the arch code resource list

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Message-ID: <Zw7za0Cp0oH6v5w6@agluck-desk3.sc.intel.com>
Date: Tue, 15 Oct 2024 15:57:47 -0700
From: Tony Luck <tony.luck@...el.com>
To: James Morse <james.morse@....com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Fenghua Yu <fenghua.yu@...el.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	H Peter Anvin <hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	shameerali.kolothum.thodi@...wei.com,
	D Scott Phillips OS <scott@...amperecomputing.com>,
	carl@...amperecomputing.com, lcherian@...vell.com,
	bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
	baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
	Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
	dfustini@...libre.com, amitsinght@...vell.com,
	David Hildenbrand <david@...hat.com>,
	Rex Nie <rex.nie@...uarmicro.com>,
	Dave Martin <dave.martin@....com>,
	Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v5 02/40] x86/resctrl: Add a helper to avoid reaching
 into the arch code resource list

On Fri, Oct 04, 2024 at 06:03:09PM +0000, James Morse wrote:
> +struct rdt_resource *resctrl_arch_get_resource(enum resctrl_res_level l)
> +{
> +	if (l >= RDT_NUM_RESOURCES)
> +		return NULL;
> +
> +	return &rdt_resources_all[l].r_resctrl;
> +}

Is this a bit fragile if someone adds a new item in enum resctrl_res_level
but doesn't add a new entry to struct rdt_hw_resource rdt_resources_all[]
in arch/x86/kernel/cpu/resctrl/core.c

Any caller of resctrl_arch_get_resource(new item name) will get past
the check "if (l >= RDT_NUM_RESOURCES)" and then return a pointer past
the end of the rdt_resources_all[] array.

Maybe make sure the array is padded out to the right size?

struct rdt_hw_resource rdt_resources_all[RDT_NUM_RESOURCES - 1] = {
	...
};

-Tony