linux-kernel - RE: [PATCH] x86/resctrl: Prevent possible overrun during bitmap operations

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Date:   Mon, 24 Jun 2019 13:55:07 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Reinette Chatre' <reinette.chatre@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "fenghua.yu@...el.com" <fenghua.yu@...el.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>
CC:     "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH] x86/resctrl: Prevent possible overrun during bitmap
 operations

From: Reinette Chatre
> Sent: 19 June 2019 21:27
> 
> While the DOC at the beginning of lib/bitmap.c explicitly states that
> "The number of valid bits in a given bitmap does _not_ need to be an
> exact multiple of BITS_PER_LONG.", some of the bitmap operations do
> indeed access BITS_PER_LONG portions of the provided bitmap no matter
> the size of the provided bitmap. For example, if find_first_bit()
> is provided with an 8 bit bitmap the operation will access
> BITS_PER_LONG bits from the provided bitmap. While the operation
> ensures that these extra bits do not affect the result, the memory
> is still accessed.

I suspect that comment also needs correcting.
On BE systems you really do need to have a array of longs.

	David

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