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lib/bitmap: extend comment for bitmap_(from,to)_arr32()

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On LE systems bitmaps are naturally ordered, therefore we can potentially
use bitmap_copy routines when converting from 32-bit arrays, even if host
system is 64-bit. But it may lead to out-of-bond access due to unsafe
typecast, and the bitmap_(from,to)_arr32 comment doesn't explain that
clearly

CC: Alexander Gordeev <agordeev@linux.ibm.com>
CC: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
CC: Christian Borntraeger <borntraeger@linux.ibm.com>
CC: Claudio Imbrenda <imbrenda@linux.ibm.com>
CC: David Hildenbrand <david@redhat.com>
CC: Heiko Carstens <hca@linux.ibm.com>
CC: Janosch Frank <frankja@linux.ibm.com>
CC: Rasmus Villemoes <linux@rasmusvillemoes.dk>
CC: Sven Schnelle <svens@linux.ibm.com>
CC: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
This commit is contained in:
Yury Norov 2022-04-28 13:51:12 -07:00
parent 6d7131bd52
commit e041e0ac53
1 changed files with 6 additions and 2 deletions
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8
include/linux/bitmap.h
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@ -264,8 +264,12 @@ static inline void bitmap_copy_clear_tail(unsigned long *dst,
}
/*
* On 32-bit systems bitmaps are represented as u32 arrays internally, and
* therefore conversion is not needed when copying data from/to arrays of u32.
* On 32-bit systems bitmaps are represented as u32 arrays internally. On LE64
* machines the order of hi and lo parts of numbers match the bitmap structure.
* In both cases conversion is not needed when copying data from/to arrays of
* u32. But in LE64 case, typecast in bitmap_copy_clear_tail() may lead
* to out-of-bound access. To avoid that, both LE and BE variants of 64-bit
* architectures are not using bitmap_copy_clear_tail().
*/
#if BITS_PER_LONG == 64
void bitmap_from_arr32(unsigned long *bitmap, const u32 *buf,