Hi Kees, On Mon, Aug 01, 2016 at 12:47:59PM -0700, Kees Cook wrote: > On Sun, Jul 31, 2016 at 1:56 PM, Jason Cooper <jason@xxxxxxxxxxxxxx> wrote: > > On Sun, Jul 31, 2016 at 09:46:53AM -0700, Kees Cook wrote: > >> On Sat, Jul 30, 2016 at 8:42 AM, Jason Cooper <jason@xxxxxxxxxxxxxx> wrote: > >> > 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(). > >> > > >> > Signed-off-by: Jason Cooper <jason@xxxxxxxxxxxxxx> > >> > --- > >> > Changes from v1: > >> > - Explicitly mention page_aligned start assumption (Yann Droneaud) > >> > - pick random pages vice random addresses (Yann Droneaud) > >> > - catch range=0 last > >> > > >> > drivers/char/random.c | 28 ++++++++++++++++++++++++++++ > >> > include/linux/random.h | 1 + > >> > 2 files changed, 29 insertions(+) > >> > > >> > diff --git a/drivers/char/random.c b/drivers/char/random.c > >> > index 0158d3bff7e5..3bedf69546d6 100644 > >> > --- a/drivers/char/random.c > >> > +++ b/drivers/char/random.c > >> > @@ -1840,6 +1840,34 @@ randomize_range(unsigned long start, unsigned long end, unsigned long len) > >> > return PAGE_ALIGN(get_random_int() % range + start); > >> > } > >> > > >> > +/** > >> > + * randomize_addr - 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. This assumption still holds. > >> > + * > >> > + * Return: A page aligned address within [start, start + range). On error, > >> > + * @start is returned. > >> > + */ > >> > +unsigned long > >> > +randomize_addr(unsigned long start, unsigned long range) > >> > >> Since we're changing other things about this, let's try to document > >> its behavior in its name too and call this "randomize_page" instead. > > > > Ack. Definitely more accurate. > > > >> If it requires a page-aligned value, we should probably also BUG_ON > >> it, or adjust the start too. > > > > merf. So, this whole series started from a suggested cleanup by William > > to s/get_random_int/get_random_long/. > > > > The current users have all been stable the way they are for a long time. > > Like pre-git long. So, if this is just a cleanup for those callers, I > > don't think we need to do more than we already are. > > > > However, if the intent is for this function to see wider use, then by > > all means, we need to handle start != PAGE_ALIGN(start). > > > > Do you have any new call sites in mind? > > I have no new call sites in mind, but it seems safe to add a BUG_ON to > verify we don't gain callers that don't follow the correct > expectations. (Or maybe WARN and return start.) No, I think BUG_ON is appropriate. afaict, the only time this will be encountered is during the development process. thx, Jason. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>