> -----Original Message----- > From: Jason Cooper [mailto:[email protected]] > Sent: Monday, July 25, 2016 8:31 PM > To: Roberts, William C <[email protected]>; linux- > [email protected]; [email protected]; kernel- > [email protected] > Cc: [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected] > Subject: Re: [RFC patch 1/6] random: Simplify API for random address requests > > All, > > On Tue, Jul 26, 2016 at 03:01:55AM +0000, Jason Cooper 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 < MAX_UINT. However, we should match caller > > expectations to avoid coming up short (ha!) in the future. > > > > Signed-off-by: Jason Cooper <[email protected]> > > --- > > drivers/char/random.c | 17 ++++------------- include/linux/random.h > > | 2 +- > > 2 files changed, 5 insertions(+), 14 deletions(-) > > > > diff --git a/drivers/char/random.c b/drivers/char/random.c index > > 0158d3bff7e5..1251cb2cbab2 100644 > > --- a/drivers/char/random.c > > +++ b/drivers/char/random.c > > @@ -1822,22 +1822,13 @@ unsigned long get_random_long(void) > > EXPORT_SYMBOL(get_random_long); > > > > /* > > - * randomize_range() returns a start address such that > > - * > > - * [...... <range> .....] > > - * start end > > - * > > - * a <range> with size "len" starting at the return value is inside > > in the > > - * area defined by [start, end], but is otherwise randomized. > > + * randomize_addr() returns a page aligned address within [start, > > + start + > > + * range] > > */ > > unsigned long > > -randomize_range(unsigned long start, unsigned long end, unsigned long > > len) > > +randomize_addr(unsigned long start, unsigned long range) > > { > > - unsigned long range = end - len - start; > > - > > - if (end <= start + len) > > - return 0; > > - return PAGE_ALIGN(get_random_int() % range + start); > > + return PAGE_ALIGN(get_random_long() % range + start); > > } > > bah! old patch file. This should have been: > > if (range == 0) > return start; > else > return PAGE_ALIGN(get_random_long() % range + start); > > sorry,
Yeah that looks better. I had a similar intended set of changes locally, because of the issues Jason pointed out. I ended up in the old case where if end - start == len it returns 0 instead of start. Jason's change is better though :-P > > Jason. > > > > > /* Interface for in-kernel drivers of true hardware RNGs. > > diff --git a/include/linux/random.h b/include/linux/random.h index > > e47e533742b5..1ad877a98186 100644 > > --- a/include/linux/random.h > > +++ b/include/linux/random.h > > @@ -34,7 +34,7 @@ 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_addr(unsigned long start, unsigned long > > +range); > > > > u32 prandom_u32(void); > > void prandom_bytes(void *buf, size_t nbytes); > > -- > > 2.9.2 > >
