@@ -13,6 +13,7 @@ struct task_struct;
 struct thread_shstk {
 	u64	base;
 	u64	size;
+	u64	locked:1;
 };
 
 #ifdef CONFIG_X86_SHADOW_STACK

@@ -41,6 +42,12 @@ static inline int setup_signal_shadow_stack(int ia32, void __user *restorer) { r
 static inline int restore_signal_shadow_stack(void) { return 0; }
 #endif
 
+#ifdef CONFIG_X86_SHADOW_STACK
+int prctl_cet(int option, u64 arg2);
+#else
+static inline int prctl_cet(int option, u64 arg2) { return -EINVAL; }
+#endif
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_CET_H */

@@ -14,4 +14,8 @@
 #define ARCH_MAP_VDSO_32	0x2002
 #define ARCH_MAP_VDSO_64	0x2003
 
+#define ARCH_X86_CET_STATUS		0x3001
+#define ARCH_X86_CET_DISABLE		0x3002
+#define ARCH_X86_CET_LOCK		0x3003
+
 #endif /* _ASM_X86_PRCTL_H */

@@ -151,6 +151,7 @@ obj-$(CONFIG_UNWINDER_GUESS)		+= unwind_guess.o
 
 obj-$(CONFIG_AMD_MEM_ENCRYPT)		+= sev.o
 obj-$(CONFIG_X86_SHADOW_STACK)		+= shstk.o
+obj-$(CONFIG_X86_SHADOW_STACK)		+= shstk.o cet_prctl.o
 ###
 # 64 bit specific files
 ifeq ($(CONFIG_X86_64),y)

@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/errno.h>
+#include <linux/uaccess.h>
+#include <linux/prctl.h>
+#include <linux/compat.h>
+#include <linux/mman.h>
+#include <linux/elfcore.h>
+#include <linux/processor.h>
+#include <asm/prctl.h>
+#include <asm/cet.h>
+
+/* See Documentation/x86/intel_cet.rst. */
+
+static int cet_copy_status_to_user(struct thread_shstk *shstk, u64 __user *ubuf)
+{
+	u64 buf[3] = {};
+
+	if (shstk->size) {
+		buf[0] |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
+		buf[1] = shstk->base;
+		buf[2] = shstk->size;
+	}
+
+	return copy_to_user(ubuf, buf, sizeof(buf));
+}
+
+int prctl_cet(int option, u64 arg2)
+{
+	struct thread_shstk *shstk;
+
+	if (!cpu_feature_enabled(X86_FEATURE_SHSTK))
+		return -ENOTSUPP;
+
+	shstk = &current->thread.shstk;
+
+	if (option == ARCH_X86_CET_STATUS)
+		return cet_copy_status_to_user(shstk, (u64 __user *)arg2);
+
+	switch (option) {
+	case ARCH_X86_CET_DISABLE:
+		if (shstk->locked)
+			return -EPERM;
+
+		if (arg2 & ~GNU_PROPERTY_X86_FEATURE_1_VALID)
+			return -EINVAL;
+		if (arg2 & GNU_PROPERTY_X86_FEATURE_1_SHSTK)
+			shstk_disable();
+		return 0;
+
+	case ARCH_X86_CET_LOCK:
+		if (arg2)
+			return -EINVAL;
+		shstk->locked = 1;
+		return 0;
+
+	default:
+		return -ENOSYS;
+	}
+}

@@ -1006,14 +1006,14 @@ unsigned long get_wchan(struct task_struct *p)
 }
 
 long do_arch_prctl_common(struct task_struct *task, int option,
-			  unsigned long cpuid_enabled)
+			  unsigned long arg2)
 {
 	switch (option) {
 	case ARCH_GET_CPUID:
 		return get_cpuid_mode();
 	case ARCH_SET_CPUID:
-		return set_cpuid_mode(task, cpuid_enabled);
+		return set_cpuid_mode(task, arg2);
 	}
 
-	return -EINVAL;
+	return prctl_cet(option, arg2);
 }