random: simplify API for random address requests
To date, all callers of randomize_range() have set the length to 0, and
check for a zero return value. For the current callers, the only way to
get zero returned is if end <= start. Since they are all adding a
constant to the start address, this is unnecessary.
We can remove a bunch of needless checks by simplifying the API to do just
what everyone wants, return an address between [start, start + range).
While we're here, s/get_random_int/get_random_long/. No current call site
is adversely affected by get_random_int(), since all current range
requests are < UINT_MAX. However, we should match caller expectations to
avoid coming up short (ha!) in the future.
All current callers to randomize_range() chose to use the start address if
randomize_range() failed. Therefore, we simplify things by just returning
the start address on error.
randomize_range() will be removed once all callers have been converted
over to randomize_addr().
Link: http://lkml.kernel.org/r/20160803233913.32511-2-jason@lakedaemon.net
Signed-off-by: Jason Cooper <jason@lakedaemon.net>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Roberts, William C" <william.c.roberts@intel.com>
Cc: Yann Droneaud <ydroneaud@opteya.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Nick Kralevich <nnk@google.com>
Cc: Jeffrey Vander Stoep <jeffv@google.com>
Cc: Daniel Cashman <dcashman@android.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 3efb3bf..40eb07e 100644
--- 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.