Messages in this thread | | | Date | Sat, 5 Oct 2013 20:05:58 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH net-next v2 3/8] x86/jump_label: expect default_nop if static_key gets enabled on boot-up |
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On Sun, 6 Oct 2013 01:20:53 +0200 Hannes Frederic Sowa <hannes@stressinduktion.org> wrote:
> net_get_random_once(intrduced in the next patch) uses static_keys in > a way that they get enabled on boot-up instead of replaced with an > ideal_nop. So check for default_nop on initial enabling. > > Other architectures don't check for this.
But they should.
> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: "H. Peter Anvin" <hpa@zytor.com> > Cc: Steven Rostedt <rostedt@goodmis.org> > Cc: Jason Baron <jbaron@redhat.com> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> > Cc: Eric Dumazet <edumazet@google.com> > Cc: "David S. Miller" <davem@davemloft.net> > Cc: x86@kernel.org > Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> > --- > arch/x86/kernel/jump_label.c | 25 ++++++++++++++++++------- > 1 file changed, 18 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c > index ee11b7d..26d5a55 100644 > --- a/arch/x86/kernel/jump_label.c > +++ b/arch/x86/kernel/jump_label.c > @@ -42,15 +42,27 @@ static void __jump_label_transform(struct jump_entry *entry, > int init) > { > union jump_code_union code; > + const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; > const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; > > if (type == JUMP_LABEL_ENABLE) { > - /* > - * We are enabling this jump label. If it is not a nop > - * then something must have gone wrong. > - */ > - if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0)) > - bug_at((void *)entry->code, __LINE__); > + if (init) { > + /* > + * Jump label is enabled for the first time. > + * So we expect a default_nop... > + */ > + if (unlikely(memcmp((void *)entry->code, default_nop, 5) > + != 0)) > + bug_at((void *)entry->code, __LINE__); > + } else { > + /* > + * ...otherwise expect an ideal_nop. Otherwise > + * something went horribly wrong. > + */ > + if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) > + != 0)) > + bug_at((void *)entry->code, __LINE__); > + }
I don't know if I like this change. This is similar to a bug we had with the Xen folks, where they didn't realize that jump labels are not suppose to be used (or set) before jump_label_init() is called.
I'll have to take a deeper look at this on Monday.
-- Steve
> > code.jump = 0xe9; > code.offset = entry->target - > @@ -63,7 +75,6 @@ static void __jump_label_transform(struct jump_entry *entry, > * are converting the default nop to the ideal nop. > */ > if (init) { > - const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; > if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0)) > bug_at((void *)entry->code, __LINE__); > } else {
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