1 files changed, 131 insertions, 0 deletions
diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
new file mode 100644
index 0000000000..d2c732a34e
--- /dev/null
+++ b/arch/x86/kernel/cet.c
@@ -0,0 +1,131 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/ptrace.h>
+#include <asm/bugs.h>
+#include <asm/traps.h>
+
+enum cp_error_code {
+	CP_EC        = (1 << 15) - 1,
+
+	CP_RET       = 1,
+	CP_IRET      = 2,
+	CP_ENDBR     = 3,
+	CP_RSTRORSSP = 4,
+	CP_SETSSBSY  = 5,
+
+	CP_ENCL	     = 1 << 15,
+};
+
+static const char cp_err[][10] = {
+	[0] = "unknown",
+	[1] = "near ret",
+	[2] = "far/iret",
+	[3] = "endbranch",
+	[4] = "rstorssp",
+	[5] = "setssbsy",
+};
+
+static const char *cp_err_string(unsigned long error_code)
+{
+	unsigned int cpec = error_code & CP_EC;
+
+	if (cpec >= ARRAY_SIZE(cp_err))
+		cpec = 0;
+	return cp_err[cpec];
+}
+
+static void do_unexpected_cp(struct pt_regs *regs, unsigned long error_code)
+{
+	WARN_ONCE(1, "Unexpected %s #CP, error_code: %s\n",
+		  user_mode(regs) ? "user mode" : "kernel mode",
+		  cp_err_string(error_code));
+}
+
+static DEFINE_RATELIMIT_STATE(cpf_rate, DEFAULT_RATELIMIT_INTERVAL,
+			      DEFAULT_RATELIMIT_BURST);
+
+static void do_user_cp_fault(struct pt_regs *regs, unsigned long error_code)
+{
+	struct task_struct *tsk;
+	unsigned long ssp;
+
+	/*
+	 * An exception was just taken from userspace. Since interrupts are disabled
+	 * here, no scheduling should have messed with the registers yet and they
+	 * will be whatever is live in userspace. So read the SSP before enabling
+	 * interrupts so locking the fpregs to do it later is not required.
+	 */
+	rdmsrl(MSR_IA32_PL3_SSP, ssp);
+
+	cond_local_irq_enable(regs);
+
+	tsk = current;
+	tsk->thread.error_code = error_code;
+	tsk->thread.trap_nr = X86_TRAP_CP;
+
+	/* Ratelimit to prevent log spamming. */
+	if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
+	    __ratelimit(&cpf_rate)) {
+		pr_emerg("%s[%d] control protection ip:%lx sp:%lx ssp:%lx error:%lx(%s)%s",
+			 tsk->comm, task_pid_nr(tsk),
+			 regs->ip, regs->sp, ssp, error_code,
+			 cp_err_string(error_code),
+			 error_code & CP_ENCL ? " in enclave" : "");
+		print_vma_addr(KERN_CONT " in ", regs->ip);
+		pr_cont("\n");
+	}
+
+	force_sig_fault(SIGSEGV, SEGV_CPERR, (void __user *)0);
+	cond_local_irq_disable(regs);
+}
+
+static __ro_after_init bool ibt_fatal = true;
+
+static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code)
+{
+	if ((error_code & CP_EC) != CP_ENDBR) {
+		do_unexpected_cp(regs, error_code);
+		return;
+	}
+
+	if (unlikely(regs->ip == (unsigned long)&ibt_selftest_noendbr)) {
+		regs->ax = 0;
+		return;
+	}
+
+	pr_err("Missing ENDBR: %pS\n", (void *)instruction_pointer(regs));
+	if (!ibt_fatal) {
+		printk(KERN_DEFAULT CUT_HERE);
+		__warn(__FILE__, __LINE__, (void *)regs->ip, TAINT_WARN, regs, NULL);
+		return;
+	}
+	BUG();
+}
+
+static int __init ibt_setup(char *str)
+{
+	if (!strcmp(str, "off"))
+		setup_clear_cpu_cap(X86_FEATURE_IBT);
+
+	if (!strcmp(str, "warn"))
+		ibt_fatal = false;
+
+	return 1;
+}
+
+__setup("ibt=", ibt_setup);
+
+DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
+{
+	if (user_mode(regs)) {
+		if (cpu_feature_enabled(X86_FEATURE_USER_SHSTK))
+			do_user_cp_fault(regs, error_code);
+		else
+			do_unexpected_cp(regs, error_code);
+	} else {
+		if (cpu_feature_enabled(X86_FEATURE_IBT))
+			do_kernel_cp_fault(regs, error_code);
+		else
+			do_unexpected_cp(regs, error_code);
+	}
+}