Messages in this thread Patch in this message | | | From | Yann Droneaud <> | Date | Thu, 04 Aug 2016 14:47:07 +0200 | Subject | Re: [PATCH v3 1/7] random: Simplify API for random address requests |
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Hi,
Le mercredi 03 août 2016 à 23:39 +0000, Jason Cooper a écrit : > > diff --git a/drivers/char/random.c b/drivers/char/random.c > index 0158d3bff7e5..61cb434e3bea 100644 > --- a/drivers/char/random.c > +++ b/drivers/char/random.c > @@ -1840,6 +1840,39 @@ randomize_range(unsigned long start, unsigned > long end, unsigned long len) > return PAGE_ALIGN(get_random_int() % range + start); > } > > +/** > + * randomize_page - Generate a random, page aligned address > + * @start: The smallest acceptable address the caller will > take. > + * @range: The size of the area, starting at @start, within > which the > + * random address must fall. > + * > + * If @start + @range would overflow, @range is capped. > + * > + * NOTE: Historical use of randomize_range, which this replaces, > presumed that > + * @start was already page aligned. We now align it regardless. > + * > + * Return: A page aligned address within [start, start + range). On > error, > + * @start is returned. > + */ > +unsigned long > +randomize_page(unsigned long start, unsigned long range) > +{
To prevent an underflow if start is not page aligned (but will one would ever use a non aligned start address *and* range ? ...)
if (range < PAGE_SIZE) return start;
> + if (!PAGE_ALIGNED(start)) { > + range -= PAGE_ALIGN(start) - start; > + start = PAGE_ALIGN(start); > + } > + > + if (start > ULONG_MAX - range) > + range = ULONG_MAX - start; > + > + range >>= PAGE_SHIFT; > + > + if (range == 0) > + return start; > + > + return start + (get_random_long() % range << PAGE_SHIFT); > +} > + > /* Interface for in-kernel drivers of true hardware RNGs. > * Those devices may produce endless random bits and will be > throttled > * when our pool is full. >
Regards.
-- Yann Droneaud OPTEYA
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