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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <ad8c7da0-3ced-0cb7-2e74-135b30fe2b64@intel.com>
Date:   Mon, 24 Jun 2019 11:19:05 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     David Laight <David.Laight@...LAB.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

Hi David,

On 6/24/2019 6:55 AM, David Laight wrote:
> 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.
> 

Thank you very much for taking a look. I believe that the lib/bitmap.c
documentation is correct, it is me that misinterpreted it and to make
matters worse I only provided the portion I misinterpreted in my commit
message. Before the portion that I quote above it is stated clearly that
it is implemented using an array of unsigned longs.

Reinette