Re: [PATCH] x86/resctrl: Prevent possible overrun during bitmap operations
From: Reinette Chatre
Date: Mon Jun 24 2019 - 14:19:10 EST
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.