x86/alternative: Add text_opcode_size()

Introduce a common helper to map *_INSN_OPCODE to *_INSN_SIZE.
Tested-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191111132457.875666061@infradead.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/text-patching.h

@@ -49,18 +49,6 @@ extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void
 extern void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate);
 extern void text_poke_finish(void);
 
-extern void *text_gen_insn(u8 opcode, const void *addr, const void *dest);
-
-extern int after_bootmem;
-extern __ro_after_init struct mm_struct *poking_mm;
-extern __ro_after_init unsigned long poking_addr;
-
-#ifndef CONFIG_UML_X86
-static inline void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
-{
-	regs->ip = ip;
-}
-
 #define INT3_INSN_SIZE		1
 #define INT3_INSN_OPCODE	0xCC
 
@@ -73,6 +61,37 @@ static inline void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
 #define JMP8_INSN_SIZE		2
 #define JMP8_INSN_OPCODE	0xEB
 
+static inline int text_opcode_size(u8 opcode)
+{
+	int size = 0;
+
+#define __CASE(insn)	\
+	case insn##_INSN_OPCODE: size = insn##_INSN_SIZE; break
+
+	switch(opcode) {
+	__CASE(INT3);
+	__CASE(CALL);
+	__CASE(JMP32);
+	__CASE(JMP8);
+	}
+
+#undef __CASE
+
+	return size;
+}
+
+extern void *text_gen_insn(u8 opcode, const void *addr, const void *dest);
+
+extern int after_bootmem;
+extern __ro_after_init struct mm_struct *poking_mm;
+extern __ro_after_init unsigned long poking_addr;
+
+#ifndef CONFIG_UML_X86
+static inline void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
+{
+	regs->ip = ip;
+}
+
 static inline void int3_emulate_push(struct pt_regs *regs, unsigned long val)
 {
 	/*

arch/x86/kernel/alternative.c

@@ -1259,22 +1259,12 @@ union text_poke_insn {
 void *text_gen_insn(u8 opcode, const void *addr, const void *dest)
 {
 	static union text_poke_insn insn; /* text_mutex */
-	int size = 0;
+	int size = text_opcode_size(opcode);
 
 	lockdep_assert_held(&text_mutex);
 
 	insn.opcode = opcode;
 
-#define __CASE(insn)	\
-	case insn##_INSN_OPCODE: size = insn##_INSN_SIZE; break
-
-	switch(opcode) {
-	__CASE(INT3);
-	__CASE(CALL);
-	__CASE(JMP32);
-	__CASE(JMP8);
-	}
-
 	if (size > 1) {
 		insn.disp = (long)dest - (long)(addr + size);
 		if (size == 2)