x86/kprobes: Convert to insn_decode()

Simplify code, improve decoding error checking.
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lkml.kernel.org/r/20210304174237.31945-12-bp@alien8.de

arch/x86/kernel/kprobes/core.c

@@ -265,6 +265,8 @@ static int can_probe(unsigned long paddr)
 	/* Decode instructions */
 	addr = paddr - offset;
 	while (addr < paddr) {
+		int ret;
+
 		/*
 		 * Check if the instruction has been modified by another
 		 * kprobe, in which case we replace the breakpoint by the
@@ -276,8 +278,10 @@ static int can_probe(unsigned long paddr)
 		__addr = recover_probed_instruction(buf, addr);
 		if (!__addr)
 			return 0;
-		kernel_insn_init(&insn, (void *)__addr, MAX_INSN_SIZE);
-		insn_get_length(&insn);
+
+		ret = insn_decode(&insn, (void *)__addr, MAX_INSN_SIZE, INSN_MODE_KERN);
+		if (ret < 0)
+			return 0;
 
 		/*
 		 * Another debugging subsystem might insert this breakpoint.
@@ -301,8 +305,8 @@ static int can_probe(unsigned long paddr)
 int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn)
 {
 	kprobe_opcode_t buf[MAX_INSN_SIZE];
-	unsigned long recovered_insn =
-		recover_probed_instruction(buf, (unsigned long)src);
+	unsigned long recovered_insn = recover_probed_instruction(buf, (unsigned long)src);
+	int ret;
 
 	if (!recovered_insn || !insn)
 		return 0;
@@ -312,8 +316,9 @@ int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn)
 			MAX_INSN_SIZE))
 		return 0;
 
-	kernel_insn_init(insn, dest, MAX_INSN_SIZE);
-	insn_get_length(insn);
+	ret = insn_decode(insn, dest, MAX_INSN_SIZE, INSN_MODE_KERN);
+	if (ret < 0)
+		return 0;
 
 	/* We can not probe force emulate prefixed instruction */
 	if (insn_has_emulate_prefix(insn))

arch/x86/kernel/kprobes/opt.c

@@ -312,6 +312,8 @@ static int can_optimize(unsigned long paddr)
 	addr = paddr - offset;
 	while (addr < paddr - offset + size) { /* Decode until function end */
 		unsigned long recovered_insn;
+		int ret;
+
 		if (search_exception_tables(addr))
 			/*
 			 * Since some fixup code will jumps into this function,
@@ -321,8 +323,11 @@ static int can_optimize(unsigned long paddr)
 		recovered_insn = recover_probed_instruction(buf, addr);
 		if (!recovered_insn)
 			return 0;
-		kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
-		insn_get_length(&insn);
+
+		ret = insn_decode(&insn, (void *)recovered_insn, MAX_INSN_SIZE, INSN_MODE_KERN);
+		if (ret < 0)
+			return 0;
+
 		/*
 		 * In the case of detecting unknown breakpoint, this could be
 		 * a padding INT3 between functions. Let's check that all the