arm64: factor insn read out of call_undef_hook()

Subsequent patches will rework EL0 UNDEF handling, removing the need for
struct undef_hook and call_undef_hook. In preparation for those changes,
this patch factors the logic for reading user instructions out of
call_undef_hook() and into a new user_insn_read() helper, matching the
style of the existing aarch64_insn_read() helper used for reading kernel
instructions.

There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20221019144123.612388-5-mark.rutland@arm.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/traps.c

@@ -394,25 +394,22 @@ void unregister_undef_hook(struct undef_hook *hook)
 	raw_spin_unlock_irqrestore(&undef_lock, flags);
 }
 
-static int call_undef_hook(struct pt_regs *regs)
+static int user_insn_read(struct pt_regs *regs, u32 *insnp)
 {
-	struct undef_hook *hook;
-	unsigned long flags;
 	u32 instr;
-	int (*fn)(struct pt_regs *regs, u32 instr) = NULL;
 	unsigned long pc = instruction_pointer(regs);
 
 	if (compat_thumb_mode(regs)) {
 		/* 16-bit Thumb instruction */
 		__le16 instr_le;
 		if (get_user(instr_le, (__le16 __user *)pc))
-			goto exit;
+			return -EFAULT;
 		instr = le16_to_cpu(instr_le);
 		if (aarch32_insn_is_wide(instr)) {
 			u32 instr2;
 
 			if (get_user(instr_le, (__le16 __user *)(pc + 2)))
-				goto exit;
+				return -EFAULT;
 			instr2 = le16_to_cpu(instr_le);
 			instr = (instr << 16) | instr2;
 		}
@@ -420,10 +417,20 @@ static int call_undef_hook(struct pt_regs *regs)
 		/* 32-bit ARM instruction */
 		__le32 instr_le;
 		if (get_user(instr_le, (__le32 __user *)pc))
-			goto exit;
+			return -EFAULT;
 		instr = le32_to_cpu(instr_le);
 	}
 
+	*insnp = instr;
+	return 0;
+}
+
+static int call_undef_hook(struct pt_regs *regs, u32 instr)
+{
+	struct undef_hook *hook;
+	unsigned long flags;
+	int (*fn)(struct pt_regs *regs, u32 instr) = NULL;
+
 	raw_spin_lock_irqsave(&undef_lock, flags);
 	list_for_each_entry(hook, &undef_hook, node)
 		if ((instr & hook->instr_mask) == hook->instr_val &&
@@ -431,7 +438,7 @@ static int call_undef_hook(struct pt_regs *regs)
 			fn = hook->fn;
 
 	raw_spin_unlock_irqrestore(&undef_lock, flags);
-exit:
+
 	return fn ? fn(regs, instr) : 1;
 }
 
@@ -483,13 +490,19 @@ void arm64_notify_segfault(unsigned long addr)
 
 void do_el0_undef(struct pt_regs *regs, unsigned long esr)
 {
+	u32 insn;
+
 	/* check for AArch32 breakpoint instructions */
 	if (!aarch32_break_handler(regs))
 		return;
 
-	if (call_undef_hook(regs) == 0)
+	if (user_insn_read(regs, &insn))
+		goto out_err;
+
+	if (call_undef_hook(regs, insn) == 0)
 		return;
 
+out_err:
 	force_signal_inject(SIGILL, ILL_ILLOPC, regs->pc, 0);
 }