[PATCH net-next v3 4/9] x86/jump_label: expect default_nop if static_key gets enabled on boot-up

[Hannes Frederic Sowa]

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@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Signed-off-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
---
 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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