From: Jason Cooper <jason@xxxxxxxxxxxxxx> Subject: 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@xxxxxxxxxxxxxx Signed-off-by: Jason Cooper <jason@xxxxxxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: "Roberts, William C" <william.c.roberts@xxxxxxxxx> Cc: Yann Droneaud <ydroneaud@xxxxxxxxxx> Cc: Russell King <linux@xxxxxxxxxxxxxxxx> Cc: "Theodore Ts'o" <tytso@xxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Paul Mackerras <paulus@xxxxxxxxx> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: "H . Peter Anvin" <hpa@xxxxxxxxx> Cc: Nick Kralevich <nnk@xxxxxxxxxx> Cc: Jeffrey Vander Stoep <jeffv@xxxxxxxxxx> Cc: Daniel Cashman <dcashman@xxxxxxxxxxx> Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx> Cc: Guan Xuetao <gxt@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/char/random.c | 33 +++++++++++++++++++++++++++++++++ include/linux/random.h | 1 + 2 files changed, 34 insertions(+) diff -puN drivers/char/random.c~random-simplify-api-for-random-address-requests drivers/char/random.c --- a/drivers/char/random.c~random-simplify-api-for-random-address-requests +++ a/drivers/char/random.c @@ -2119,6 +2119,39 @@ randomize_range(unsigned long start, uns 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. diff -puN include/linux/random.h~random-simplify-api-for-random-address-requests include/linux/random.h --- a/include/linux/random.h~random-simplify-api-for-random-address-requests +++ a/include/linux/random.h @@ -35,6 +35,7 @@ extern const struct file_operations rand 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); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
