[PATCH RFC 2/4] x86/arch_prctl: add ARCH_GET_NOPTI and ARCH_SET_NOPTI to enable/disable PTI

[Willy Tarreau]

This allows to report the current state of the PTI protection and to
enable or disable it for the current task.

Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 arch/x86/include/uapi/asm/prctl.h |  3 +++
 arch/x86/kernel/process_64.c      | 24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index 5a6aac9..1f1b5bc 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -10,6 +10,9 @@
 #define ARCH_GET_CPUID		0x1011
 #define ARCH_SET_CPUID		0x1012
 
+#define ARCH_GET_NOPTI		0x1021
+#define ARCH_SET_NOPTI		0x1022
+
 #define ARCH_MAP_VDSO_X32	0x2001
 #define ARCH_MAP_VDSO_32	0x2002
 #define ARCH_MAP_VDSO_64	0x2003
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index c754662..1686d3d 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -654,6 +654,30 @@ long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
 		ret = put_user(base, (unsigned long __user *)arg2);
 		break;
 	}
+	case ARCH_GET_NOPTI: {
+		unsigned long flag;
+
+		printk(KERN_DEBUG "get1: task=%p ti=%p fl=%16lx\n", task, task_thread_info(task), task_thread_info(task)->flags);
+		flag = !!(task_thread_info(task)->flags & _TIF_NOPTI);
+		ret = put_user(flag, (unsigned long __user *)arg2);
+		break;
+	}
+
+	case ARCH_SET_NOPTI:
+		if (!capable(CAP_SYS_RAWIO))
+			return -EPERM;
+
+		printk(KERN_DEBUG "set1: task=%p ti=%p fl=%16lx doit=%d arg2=%ld\n", task, task_thread_info(task), task_thread_info(task)->flags, doit, arg2);
+
+		if (doit) {
+			if (arg2)
+				task_thread_info(task)->flags |= _TIF_NOPTI;
+			else
+				task_thread_info(task)->flags &= ~_TIF_NOPTI;
+
+			printk(KERN_DEBUG "set2: task=%p ti=%p fl=%16lx\n", task, task_thread_info(task), task_thread_info(task)->flags);
+		}
+		break;
 
 #ifdef CONFIG_CHECKPOINT_RESTORE
 # ifdef CONFIG_X86_X32_ABI
-- 
1.7.12.1