Messages in this thread | | | Date | Fri, 15 May 2009 09:16:17 +0800 | Subject | Re: [patch] random: make get_random_int() more random | From | Américo Wang <> |
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On Thu, May 7, 2009 at 4:09 AM, Ingo Molnar <mingo@elte.hu> wrote: > > * Linus Torvalds <torvalds@linux-foundation.org> wrote: > >> On Wed, 6 May 2009, Matt Mackall wrote: >> >> > On Wed, May 06, 2009 at 12:30:34PM +0200, Ingo Molnar wrote: >> >> > > (Also, obviously "only" covering 95% of the Linux systems has >> > > its use as well. Most other architectures have their own cycle >> > > counters as well.) >> > >> > X86 might be 95% of desktop. But it's a small fraction of Linux >> > systems once you count cell phones, video players, TVs, cameras, >> > GPS devices, cars, routers, etc. almost none of which are >> > x86-based. In fact, just Linux cell phones (with about an 8% >> > share of a 1.2billion devices per year market) dwarf Linux >> > desktops (maybe 5% of a 200m/y market). >> >> Matt, are you willing to ack my suggested patch which adds history >> to the mix? Did somebody test that? I have this memory of there >> being an "exploit" program to show the non-randomness of the >> values, but I can't recall details, and would really want to get a >> second opinion from somebody who cares about PRNG's. > > I tested it, and besides booting up fine, i also tested the > get_random_int() randomness. I did this by adding this quick > trace_printk() line: > > trace_printk("get_random_int(): %08x\n", get_random_int()); > > to sys_prctl() and triggered sys_prctl() in a loop, which gave a > list of get_random_int() numbers: > > # tracer: nop > # > # TASK-PID CPU# TIMESTAMP FUNCTION > # | | | | | > <...>-6288 [000] 618.151323: sys_prctl: get_random_int(): 2e927f66 > <...>-6290 [000] 618.152924: sys_prctl: get_random_int(): d210df1f > <...>-6293 [000] 618.155326: sys_prctl: get_random_int(): 753ad860 > <...>-6295 [000] 618.156939: sys_prctl: get_random_int(): c74d935f > <...>-6298 [000] 618.159334: sys_prctl: get_random_int(): bb4e7597 > <...>-6300 [000] 618.160936: sys_prctl: get_random_int(): b0119885 > <...>-6303 [000] 618.163331: sys_prctl: get_random_int(): 093f5c70 >
I used systemtap to test this patch too, the result is too obvious. :-) Samples of output are the following:
==before this patch== get_random_int returns: f3f71569 get_random_int returns: f3f71569 get_random_int returns: f3f71569 get_random_int returns: f3f71569 get_random_int returns: f3f71569 get_random_int returns: f3f71569 get_random_int returns: c3e650c8 get_random_int returns: c3e650c8 get_random_int returns: c3e650c8 get_random_int returns: c3e650c8 get_random_int returns: c3e650c8 get_random_int returns: c3e650c8
==after this patch== get_random_int returns: b7566a5b get_random_int returns: f4b86171 get_random_int returns: 25dd8fd8 get_random_int returns: 58ab81ce get_random_int returns: f39dbcb2 get_random_int returns: cbf308f9 get_random_int returns: 32d9c09e get_random_int returns: 4eedfcad get_random_int returns: fe87cb99 get_random_int returns: 1bd42857 get_random_int returns: 837cf921 get_random_int returns: d9a39d80
Hope this helps.
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