x86/static_call: Serialize __static_call_fixup() properly

__static_call_fixup() invokes __static_call_transform() without holding
text_mutex, which causes lockdep to complain in text_poke_bp().

Adding the proper locking cures that, but as this is either used during
early boot or during module finalizing, it's not required to use
text_poke_bp(). Add an argument to __static_call_transform() which tells
it to use text_poke_early() for it.

Fixes: ee88d363 ("x86,static_call: Use alternative RET encoding")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>

arch/x86/kernel/static_call.c

@@ -25,7 +25,8 @@ static const u8 xor5rax[] = { 0x2e, 0x2e, 0x2e, 0x31, 0xc0 };
 
 static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
 
-static void __ref __static_call_transform(void *insn, enum insn_type type, void *func)
+static void __ref __static_call_transform(void *insn, enum insn_type type,
+					  void *func, bool modinit)
 {
 	const void *emulate = NULL;
 	int size = CALL_INSN_SIZE;
@@ -60,7 +61,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, void
 	if (memcmp(insn, code, size) == 0)
 		return;
 
-	if (unlikely(system_state == SYSTEM_BOOTING))
+	if (system_state == SYSTEM_BOOTING || modinit)
 		return text_poke_early(insn, code, size);
 
 	text_poke_bp(insn, code, size, emulate);
@@ -114,12 +115,12 @@ void arch_static_call_transform(void *site, void *tramp, void *func, bool tail)
 
 	if (tramp) {
 		__static_call_validate(tramp, true, true);
-		__static_call_transform(tramp, __sc_insn(!func, true), func);
+		__static_call_transform(tramp, __sc_insn(!func, true), func, false);
 	}
 
 	if (IS_ENABLED(CONFIG_HAVE_STATIC_CALL_INLINE) && site) {
 		__static_call_validate(site, tail, false);
-		__static_call_transform(site, __sc_insn(!func, tail), func);
+		__static_call_transform(site, __sc_insn(!func, tail), func, false);
 	}
 
 	mutex_unlock(&text_mutex);
@@ -145,8 +146,10 @@ bool __static_call_fixup(void *tramp, u8 op, void *dest)
 		return false;
 	}
 
+	mutex_lock(&text_mutex);
 	if (op == RET_INSN_OPCODE || dest == &__x86_return_thunk)
-		__static_call_transform(tramp, RET, NULL);
+		__static_call_transform(tramp, RET, NULL, true);
+	mutex_unlock(&text_mutex);
 
 	return true;
 }