4 files changed, 89 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
index 56a9e63b6c33..1bb043018315 100644
--- a/arch/arm64/include/asm/insn.h
+++ b/arch/arm64/include/asm/insn.h
@@ -354,6 +354,8 @@ bool aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn);
 int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
 int aarch64_insn_patch_text_sync(void *addrs[], u32 insns[], int cnt);
 int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
+
+bool aarch32_insn_is_wide(u32 insn);
 #endif /* __ASSEMBLY__ */
 
 #endif	/* __ASM_INSN_H */
diff --git a/arch/arm64/include/asm/traps.h b/arch/arm64/include/asm/traps.h
index 10ca8ff93cc2..232e4ba5d314 100644
--- a/arch/arm64/include/asm/traps.h
+++ b/arch/arm64/include/asm/traps.h
@@ -18,6 +18,22 @@
 #ifndef __ASM_TRAP_H
 #define __ASM_TRAP_H
 
+#include <linux/list.h>
+
+struct pt_regs;
+
+struct undef_hook {
+	struct list_head node;
+	u32 instr_mask;
+	u32 instr_val;
+	u64 pstate_mask;
+	u64 pstate_val;
+	int (*fn)(struct pt_regs *regs, u32 instr);
+};
+
+void register_undef_hook(struct undef_hook *hook);
+void unregister_undef_hook(struct undef_hook *hook);
+
 static inline int in_exception_text(unsigned long ptr)
 {
 	extern char __exception_text_start[];
diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
index e007714ded04..ab00eb58d385 100644
--- a/arch/arm64/kernel/insn.c
+++ b/arch/arm64/kernel/insn.c
@@ -959,3 +959,8 @@ u32 aarch64_insn_gen_logical_shifted_reg(enum aarch64_insn_register dst,
 
 	return aarch64_insn_encode_immediate(AARCH64_INSN_IMM_6, insn, shift);
 }
+
+bool aarch32_insn_is_wide(u32 insn)
+{
+	return insn >= 0xe800;
+}
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index de1b085e7963..0a801e3743d5 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -259,6 +259,69 @@ void arm64_notify_die(const char *str, struct pt_regs *regs,
 	}
 }
 
+static LIST_HEAD(undef_hook);
+static DEFINE_RAW_SPINLOCK(undef_lock);
+
+void register_undef_hook(struct undef_hook *hook)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&undef_lock, flags);
+	list_add(&hook->node, &undef_hook);
+	raw_spin_unlock_irqrestore(&undef_lock, flags);
+}
+
+void unregister_undef_hook(struct undef_hook *hook)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&undef_lock, flags);
+	list_del(&hook->node);
+	raw_spin_unlock_irqrestore(&undef_lock, flags);
+}
+
+static int call_undef_hook(struct pt_regs *regs)
+{
+	struct undef_hook *hook;
+	unsigned long flags;
+	u32 instr;
+	int (*fn)(struct pt_regs *regs, u32 instr) = NULL;
+	void __user *pc = (void __user *)instruction_pointer(regs);
+
+	if (!user_mode(regs))
+		return 1;
+
+	if (compat_thumb_mode(regs)) {
+		/* 16-bit Thumb instruction */
+		if (get_user(instr, (u16 __user *)pc))
+			goto exit;
+		instr = le16_to_cpu(instr);
+		if (aarch32_insn_is_wide(instr)) {
+			u32 instr2;
+
+			if (get_user(instr2, (u16 __user *)(pc + 2)))
+				goto exit;
+			instr2 = le16_to_cpu(instr2);
+			instr = (instr << 16) | instr2;
+		}
+	} else {
+		/* 32-bit ARM instruction */
+		if (get_user(instr, (u32 __user *)pc))
+			goto exit;
+		instr = le32_to_cpu(instr);
+	}
+
+	raw_spin_lock_irqsave(&undef_lock, flags);
+	list_for_each_entry(hook, &undef_hook, node)
+		if ((instr & hook->instr_mask) == hook->instr_val &&
+			(regs->pstate & hook->pstate_mask) == hook->pstate_val)
+			fn = hook->fn;
+
+	raw_spin_unlock_irqrestore(&undef_lock, flags);
+exit:
+	return fn ? fn(regs, instr) : 1;
+}
+
 asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
 {
 	siginfo_t info;
@@ -268,6 +331,9 @@ asmlinkage void __exception do_undefinstr(struct pt_regs *regs)
 	if (!aarch32_break_handler(regs))
 		return;
 
+	if (call_undef_hook(regs) == 0)
+		return;
+
 	if (show_unhandled_signals && unhandled_signal(current, SIGILL) &&
 	    printk_ratelimit()) {
 		pr_info("%s[%d]: undefined instruction: pc=%p\n",