x86/jump_label: expect default_nop if static_key gets enabled on boot-up

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 18 insertions, 7 deletions

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index ee11b7dfbfbb..26d5a55a2736 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 {