linux-kernel - Re: [PATCH v4] x86/resctrl: Avoid overflow in MB settings in bw

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Message-ID: <5b49b43e-f94c-4294-84a0-ebc413223dc1@intel.com>
Date: Thu, 3 Oct 2024 08:17:45 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Martin Kletzander <nert.pinx@...il.com>, Fenghua Yu
	<fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
	<mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] x86/resctrl: Avoid overflow in MB settings in
 bw_validate()

Hi Martin,

On 10/1/24 4:43 AM, Martin Kletzander wrote:
> The resctrl schemata file supports specifying memory bandwidth
> associated with the Memory Bandwidth Allocation (MBA) feature
> via a percentage (this is the default) or bandwidth in MiBps
> (when resctrl is mounted with the "mba_MBps" option). The allowed
> range for the bandwidth percentage is from
> /sys/fs/resctrl/info/MB/min_bandwidth to 100, using a granularity
> of /sys/fs/resctrl/info/MB/bandwidth_gran. The supported range for
> the MiBps bandwidth is 0 to U32_MAX.
> 
> There are two issues with parsing of MiBps memory bandwidth:
> * The user provided MiBps is mistakenly rounded up to the granularity
>   that is unique to percentage input.
> * The user provided MiBps is parsed using unsigned long (thus accepting
>   values up to ULONG_MAX), and then assigned to u32 that could result in
>   overflow.
> 
> Do not round up the MiBps value and parse user provided bandwidth as
> the u32 it is intended to be. Use the appropriate kstrtou32() that
> can detect out of range values.
> 
> Fixes: 8205a078ba78 ("x86/intel_rdt/mba_sc: Add schemata support")
> Fixes: 6ce1560d35f6 ("x86/resctrl: Switch over to the resctrl mbps_val list")
> Co-developed-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Martin Kletzander <nert.pinx@...il.com>
> ---

Thank you very much.

Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette