From: Reinette Chatre <reinette.chatre@intel.com>
To: David Laight <David.Laight@ACULAB.COM>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"fenghua.yu@intel.com" <fenghua.yu@intel.com>,
"bp@alien8.de" <bp@alien8.de>,
"tony.luck@intel.com" <tony.luck@intel.com>
Cc: "mingo@redhat.com" <mingo@redhat.com>,
"hpa@zytor.com" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH] x86/resctrl: Prevent possible overrun during bitmap operations
Date: Mon, 24 Jun 2019 11:19:05 -0700 [thread overview]
Message-ID: <ad8c7da0-3ced-0cb7-2e74-135b30fe2b64@intel.com> (raw)
In-Reply-To: <2b15f4ce814a425c8278e910289398c1@AcuMS.aculab.com>
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
prev parent reply other threads:[~2019-06-24 18:19 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-19 20:27 [PATCH] x86/resctrl: Prevent possible overrun during bitmap operations Reinette Chatre
2019-06-20 13:44 ` Borislav Petkov
2019-06-20 23:24 ` Reinette Chatre
2019-06-20 13:49 ` [tip:x86/urgent] " tip-bot for Reinette Chatre
2019-06-24 13:55 ` [PATCH] " David Laight
2019-06-24 18:19 ` Reinette Chatre [this message]
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