Enable 64 bit processes to use compat input syscalls

The compat variant of input syscalls is only enabled for 32 bit tasks, but in some cases, such as userspace emulation, it's useful to enable that variant for 64 bit processes. Here we introduce the PR_[GET|SET]_COMPAT_INPUT prctl to allow 64 bit tasks to opt-in for compat input syscalls. Signed-off-by: Sergio Lopez <[email protected]>
slp · Oct 8, 2024 · 897560f · 897560f
1 parent 95ae01a
commit 897560f
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Showing 5 changed files with 29 additions and 4 deletions.
diff --git a/drivers/input/input-compat.c b/drivers/input/input-compat.c
@@ -14,7 +14,7 @@
 int input_event_from_user(const char __user *buffer,
 			  struct input_event *event)
 {
-	if (in_compat_syscall() && !COMPAT_USE_64BIT_TIME) {
+	if (current->compat_input || (in_compat_syscall() && !COMPAT_USE_64BIT_TIME)) {
 		struct input_event_compat compat_event;
 
 		if (copy_from_user(&compat_event, buffer,
@@ -38,7 +38,7 @@ int input_event_from_user(const char __user *buffer,
 int input_event_to_user(char __user *buffer,
 			const struct input_event *event)
 {
-	if (in_compat_syscall() && !COMPAT_USE_64BIT_TIME) {
+	if (current->compat_input || (in_compat_syscall() && !COMPAT_USE_64BIT_TIME)) {
 		struct input_event_compat compat_event;
 
 		compat_event.sec = event->input_event_sec;
@@ -62,7 +62,7 @@ int input_event_to_user(char __user *buffer,
 int input_ff_effect_from_user(const char __user *buffer, size_t size,
 			      struct ff_effect *effect)
 {
-	if (in_compat_syscall()) {
+	if (current->compat_input || (in_compat_syscall() && !COMPAT_USE_64BIT_TIME)) {
 		struct ff_effect_compat *compat_effect;
 
 		if (size != sizeof(struct ff_effect_compat))

diff --git a/drivers/input/input-compat.h b/drivers/input/input-compat.h
@@ -53,7 +53,7 @@ struct ff_effect_compat {
 
 static inline size_t input_event_size(void)
 {
-	return (in_compat_syscall() && !COMPAT_USE_64BIT_TIME) ?
+	return (current->compat_input || (in_compat_syscall() && !COMPAT_USE_64BIT_TIME)) ?
 		sizeof(struct input_event_compat) : sizeof(struct input_event);
 }
 

diff --git a/include/linux/sched.h b/include/linux/sched.h
@@ -1535,6 +1535,11 @@ struct task_struct {
 #ifdef CONFIG_USER_EVENTS
 	struct user_event_mm		*user_event_mm;
 #endif
+	/*
+	 * Whether the task wants to use compat input syscalls even if it's
+	 * a 64-bit process.
+	 */
+	bool compat_input;
 
 	/*
 	 * New fields for task_struct should be added above here, so that

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
@@ -311,4 +311,9 @@ struct prctl_mm_map {
 # define PR_SET_MEM_MODEL_DEFAULT	0
 # define PR_SET_MEM_MODEL_TSO		1
 
+#define PR_GET_COMPAT_INPUT    0x63494e50
+#define PR_SET_COMPAT_INPUT    0x43494e50
+# define PR_SET_COMPAT_INPUT_DISABLE  0
+# define PR_SET_COMPAT_INPUT_ENABLE   1
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
@@ -2768,6 +2768,21 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			return -EINVAL;
 		error = arch_prctl_mem_model_set(me, arg2);
 		break;
+	case PR_GET_COMPAT_INPUT:
+		if (arg2 || arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = current->compat_input;
+		break;
+	case PR_SET_COMPAT_INPUT:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+		if (arg2 == PR_SET_COMPAT_INPUT_DISABLE)
+			current->compat_input = false;
+		else if (arg2 == PR_SET_COMPAT_INPUT_ENABLE)
+			current->compat_input = true;
+		else
+			return -EINVAL;
+		break;
 	default:
 		error = -EINVAL;
 		break;