On Sun, 6 Oct 2013 01:20:53 +0200
Hannes Frederic Sowa <han...@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 <t...@linutronix.de>
> Cc: Ingo Molnar <mi...@redhat.com>
> Cc: "H. Peter Anvin" <h...@zytor.com>
> Cc: Steven Rostedt <rost...@goodmis.org>
> Cc: Jason Baron <jba...@redhat.com>
> Cc: Peter Zijlstra <a.p.zijls...@chello.nl>
> Cc: Eric Dumazet <eduma...@google.com>
> Cc: "David S. Miller" <da...@davemloft.net>
> Cc: x...@kernel.org
> Signed-off-by: Hannes Frederic Sowa <han...@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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