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    Subject[PATCH net-next v4 4/9] x86/jump_label: expect default_nop if static_key gets enabled on boot-up
    Date
    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.

    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__);
    + }

    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 {
    --
    1.8.3.1


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