Re: [PATCH v3 1/7] random: Simplify API for random address requests
From: Yann Droneaud <hidden>
Date: 2016-08-04 12:47:43
Also in:
lkml
Hi, Le mercredi 03 aoA>>t 2016 A 23:39 +0000, Jason Cooper a A(C)critA :
quoted hunk ↗ jump to hunk
Adiff --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, unsignedlong end, unsigned long len) A return PAGE_ALIGN(get_random_int() % range + start); A } A +/** + * 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.A A We now align it regardless. + * + * Return: A page aligned address within [start, start + range).A A 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 ? ...) A A A A A A A A if (range < PAGE_SIZE) A A A A A A A A A A A A A A A A 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);
+}
+
A /* Interface for in-kernel drivers of true hardware RNGs.
A * Those devices may produce endless random bits and will be
throttled
A * when our pool is full.
A Regards. --A Yann Droneaud OPTEYA -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>