linux-kernel - [PATCH v2 5/8] x86: jump_label: switch to jump

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Date:   Mon,  2 Jul 2018 20:11:42 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-arch@...r.kernel.org
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Jessica Yu <jeyu@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v2 5/8] x86: jump_label: switch to jump_entry accessors

In preparation of switching x86 to use place-relative references for
the code, target and key members of struct jump_entry, replace direct
references to the struct members with invocations of the new accessors.
This will allow us to make the switch by modifying the accessors only.

This incorporates a cleanup of __jump_label_transform() proposed by
Peter.

Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 arch/x86/kernel/jump_label.c | 62 ++++++++------------
 1 file changed, 25 insertions(+), 37 deletions(-)

diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c
index e56c95be2808..023768222a94 100644
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -42,52 +42,37 @@ static void __jump_label_transform(struct jump_entry *entry,
 				   void *(*poker)(void *, const void *, size_t),
 				   int init)
 {
-	union jump_code_union code;
+	union jump_code_union jmp;
 	const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 	const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
+	const void *expect, *code;
+	int line;
+
+	jmp.jump = 0xe9;
+	jmp.offset = jump_entry_target(entry) -
+		     (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 
 	if (type == JUMP_LABEL_JMP) {
 		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__);
+			expect = default_nop; line = __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__);
+			expect = ideal_nop; line = __LINE__;
 		}
 
-		code.jump = 0xe9;
-		code.offset = entry->target -
-				(entry->code + JUMP_LABEL_NOP_SIZE);
+		code = &jmp.code;
 	} else {
-		/*
-		 * We are disabling this jump label. If it is not what
-		 * we think it is, then something must have gone wrong.
-		 * If this is the first initialization call, then we
-		 * are converting the default nop to the ideal nop.
-		 */
 		if (init) {
-			if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
-				bug_at((void *)entry->code, __LINE__);
+			expect = default_nop; line = __LINE__;
 		} else {
-			code.jump = 0xe9;
-			code.offset = entry->target -
-				(entry->code + JUMP_LABEL_NOP_SIZE);
-			if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
-				bug_at((void *)entry->code, __LINE__);
+			expect = &jmp.code; line = __LINE__;
 		}
-		memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
+
+		code = ideal_nop;
 	}
 
+	if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
+		bug_at((void *)jump_entry_code(entry), line);
+
 	/*
 	 * Make text_poke_bp() a default fallback poker.
 	 *
@@ -96,11 +81,14 @@ static void __jump_label_transform(struct jump_entry *entry,
 	 * always nop being the 'currently valid' instruction
 	 *
 	 */
-	if (poker)
-		(*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
-	else
-		text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
-			     (void *)entry->code + JUMP_LABEL_NOP_SIZE);
+	if (poker) {
+		(*poker)((void *)jump_entry_code(entry), code,
+			 JUMP_LABEL_NOP_SIZE);
+		return;
+	}
+
+	text_poke_bp((void *)jump_entry_code(entry), code, JUMP_LABEL_NOP_SIZE,
+		     (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
 }
 
 void arch_jump_label_transform(struct jump_entry *entry,
-- 
2.17.1