Re: [RFC PATCH v4 06/27] x86/cet: Control protection exception handler

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index e6db475164ed..873765adc244 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c

@@ -578,6 +578,64 @@ do_general_protection(struct pt_regs *regs, long error_code)
 }
 NOKPROBE_SYMBOL(do_general_protection);
 
+static const char *control_protection_err[] =
+{
+	"unknown",
+	"near-ret",
+	"far-ret/iret",
+	"endbranch",
+	"rstorssp",
+	"setssbsy",
+};
+
+/*
+ * When a control protection exception occurs, send a signal
+ * to the responsible application.  Currently, control
+ * protection is only enabled for the user mode.  This
+ * exception should not come from the kernel mode.
+ */
+dotraplinkage void
+do_control_protection(struct pt_regs *regs, long error_code)
+{
+	struct task_struct *tsk;
+
+	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
+	if (notify_die(DIE_TRAP, "control protection fault", regs,
+		       error_code, X86_TRAP_CP, SIGSEGV) == NOTIFY_STOP)
+		return;
+	cond_local_irq_enable(regs);
+
+	if (!user_mode(regs))
+		die("kernel control protection fault", regs, error_code);
+
+	if (!static_cpu_has(X86_FEATURE_SHSTK) &&
+	    !static_cpu_has(X86_FEATURE_IBT))
+		WARN_ONCE(1, "CET is disabled but got control "
+			  "protection fault\n");
+
+	tsk = current;
+	tsk->thread.error_code = error_code;
+	tsk->thread.trap_nr = X86_TRAP_CP;
+
+	if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
+	    printk_ratelimit()) {
+		unsigned int max_err;
+
+		max_err = ARRAY_SIZE(control_protection_err) - 1;
+		if ((error_code < 0) || (error_code > max_err))
+			error_code = 0;
+		pr_info("%s[%d] control protection ip:%lx sp:%lx error:%lx(%s)",
+			tsk->comm, task_pid_nr(tsk),
+			regs->ip, regs->sp, error_code,
+			control_protection_err[error_code]);
+		print_vma_addr(KERN_CONT " in ", regs->ip);
+		pr_cont("\n");
+	}
+
+	force_sig_info(SIGSEGV, SEND_SIG_PRIV, tsk);