From: Yury Norov > Sent: 20 April 2022 23:25 > > Manipulating 64-bit arrays with bitmap functions is potentially dangerous > because on 32-bit BE machines the order of halfwords doesn't match. Another > issue is that compiler may throw a warning about out-of-boundary access. > > This patch adds bitmap_{from,to}_arr64 functions in addition to existing > bitmap_{from,to}_arr32. > > Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx> > --- > include/linux/bitmap.h | 23 +++++++++++++++++---- > lib/bitmap.c | 47 ++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 66 insertions(+), 4 deletions(-) > > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h > index 10d805c2893c..f78c534fb814 100644 > --- a/include/linux/bitmap.h > +++ b/include/linux/bitmap.h > @@ -292,6 +292,24 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, > (const unsigned long *) (bitmap), (nbits)) > #endif > > +/* > + * On 64-bit systems bitmaps are represented as u64 arrays internally. On LE32 > + * machines the order of hi and lo parts of nubmers match the bitmap structure. > + * In both cases conversion is not needed when copying data from/to arrays of > + * u64. > + */ > +#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN) I think I'd change the condition to (inverting it): #if (BITS_PER_LONG == 64) || defined(__LITTLE_ENDIAN) since that is the condition when the layout matches. > +void bitmap_from_arr64(unsigned long *bitmap, const u64 *buf, unsigned int nbits); > +void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits); > +#else > +#define bitmap_from_arr64(bitmap, buf, nbits) \ > + bitmap_copy_clear_tail((unsigned long *) (bitmap), \ > + (const unsigned long *) (buf), (nbits)) > +#define bitmap_to_arr64(buf, bitmap, nbits) \ > + bitmap_copy_clear_tail((unsigned long *) (buf), \ > + (const unsigned long *) (bitmap), (nbits)) > +#endif > + > static inline int bitmap_and(unsigned long *dst, const unsigned long *src1, > const unsigned long *src2, unsigned int nbits) > { > @@ -596,10 +614,7 @@ static inline void bitmap_next_set_region(unsigned long *bitmap, > */ > static inline void bitmap_from_u64(unsigned long *dst, u64 mask) > { > - dst[0] = mask & ULONG_MAX; > - > - if (sizeof(mask) > sizeof(unsigned long)) > - dst[1] = mask >> 32; > + bitmap_from_arr64(dst, &mask, 64); > } I'd leave this alone. > > /** > diff --git a/lib/bitmap.c b/lib/bitmap.c > index d9a4480af5b9..aea9493f4216 100644 > --- a/lib/bitmap.c > +++ b/lib/bitmap.c > @@ -1533,5 +1533,52 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits) > buf[halfwords - 1] &= (u32) (UINT_MAX >> ((-nbits) & 31)); > } > EXPORT_SYMBOL(bitmap_to_arr32); > +#endif > + > +#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN) > +/** > + * bitmap_from_arr64 - copy the contents of u64 array of bits to bitmap > + * @bitmap: array of unsigned longs, the destination bitmap > + * @buf: array of u64 (in host byte order), the source bitmap > + * @nbits: number of bits in @bitmap > + */ > +void bitmap_from_arr64(unsigned long *bitmap, const u64 *buf, unsigned int nbits) > +{ > + while (nbits > 0) { This looks like a for look to me... > + u64 val = *buf++; > + > + *bitmap++ = (unsigned long)val; > + if (nbits > 32) > + *bitmap++ = (unsigned long)(val >> 32); No need for either cast. > + nbits -= 64; > + } > > + /* Clear tail bits in last word beyond nbits. */ > + if (nbits % BITS_PER_LONG) > + bitmap[-1] &= BITMAP_LAST_WORD_MASK(nbits); > +} > +EXPORT_SYMBOL(bitmap_from_arr64); > + > +/** > + * bitmap_to_arr64 - copy the contents of bitmap to a u64 array of bits > + * @buf: array of u64 (in host byte order), the dest bitmap > + * @bitmap: array of unsigned longs, the source bitmap > + * @nbits: number of bits in @bitmap > + */ > +void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits) > +{ > + unsigned long *end = bitmap + BITS_TO_LONGS(nbits); > + > + while (bitmap < end) { Another for loop... > + *buf = *bitmap++; > + if (bitmap < end) > + *buf |= *bitmap++ << 32; That is UB. Did you even compile this?? David > + buf++; > + } > + > + /* Clear tail bits in last element of array beyond nbits. */ > + if (nbits % 64) > + buf[-1] &= GENMASK_ULL(nbits, 0); > +} > +EXPORT_SYMBOL(bitmap_to_arr64); > #endif > -- > 2.32.0 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)