Commit 99fdafde authored by Jason Cooper's avatar Jason Cooper Committed by Linus Torvalds

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: default avatarJason Cooper <>
Acked-by: default avatarKees Cook <>
Cc: Michael Ellerman <>
Cc: "Roberts, William C" <>
Cc: Yann Droneaud <>
Cc: Russell King <>
Cc: "Theodore Ts'o" <>
Cc: Arnd Bergmann <>
Cc: Greg Kroah-Hartman <>
Cc: Catalin Marinas <>
Cc: Will Deacon <>
Cc: Ralf Baechle <>
Cc: Benjamin Herrenschmidt <>
Cc: Paul Mackerras <>
Cc: "David S. Miller" <>
Cc: Thomas Gleixner <>
Cc: Ingo Molnar <>
Cc: "H . Peter Anvin" <>
Cc: Nick Kralevich <>
Cc: Jeffrey Vander Stoep <>
Cc: Daniel Cashman <>
Cc: Chris Metcalf <>
Cc: Guan Xuetao <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 7836a2d9
......@@ -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.
......@@ -35,6 +35,7 @@ extern const struct file_operations random_fops, urandom_fops;
unsigned int get_random_int(void);
unsigned long get_random_long(void);
unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);
unsigned long randomize_page(unsigned long start, unsigned long range);
u32 prandom_u32(void);
void prandom_bytes(void *buf, size_t nbytes);
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