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

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Message-ID: <ZvxaCamN7FP-TX2s@agluck-desk3.sc.intel.com>
Date: Tue, 1 Oct 2024 13:22:33 -0700
From: Tony Luck <tony.luck@...el.com>
To: Martin Kletzander <nert.pinx@...il.com>
Cc: 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>,
	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()

On Tue, Oct 01, 2024 at 01:43:56PM +0200, 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>

Reviewed-by: Tony Luck <tony.luck@...el.com>

-Tony