random: simplify API for random address requests

[cascardo/linux.git] / drivers / char / random.c

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 3efb3bf..40eb07e 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2119,6 +2119,39 @@ 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)
+{
+       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.