1 files changed, 249 insertions, 0 deletions
diff --git a/drivers/misc/ntsync.c b/drivers/misc/ntsync.c
new file mode 100644
index 000000000000..3c2f743c58b0
--- /dev/null
+++ b/drivers/misc/ntsync.c
@@ -0,0 +1,249 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ntsync.c - Kernel driver for NT synchronization primitives
+ *
+ * Copyright (C) 2024 Elizabeth Figura <zfigura@codeweavers.com>
+ */
+
+#include <linux/anon_inodes.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/overflow.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <uapi/linux/ntsync.h>
+
+#define NTSYNC_NAME	"ntsync"
+
+enum ntsync_type {
+	NTSYNC_TYPE_SEM,
+};
+
+/*
+ * Individual synchronization primitives are represented by
+ * struct ntsync_obj, and each primitive is backed by a file.
+ *
+ * The whole namespace is represented by a struct ntsync_device also
+ * backed by a file.
+ *
+ * Both rely on struct file for reference counting. Individual
+ * ntsync_obj objects take a reference to the device when created.
+ */
+
+struct ntsync_obj {
+	spinlock_t lock;
+
+	enum ntsync_type type;
+
+	struct file *file;
+	struct ntsync_device *dev;
+
+	/* The following fields are protected by the object lock. */
+	union {
+		struct {
+			__u32 count;
+			__u32 max;
+		} sem;
+	} u;
+};
+
+struct ntsync_device {
+	struct file *file;
+};
+
+/*
+ * Actually change the semaphore state, returning -EOVERFLOW if it is made
+ * invalid.
+ */
+static int post_sem_state(struct ntsync_obj *sem, __u32 count)
+{
+	__u32 sum;
+
+	lockdep_assert_held(&sem->lock);
+
+	if (check_add_overflow(sem->u.sem.count, count, &sum) ||
+	    sum > sem->u.sem.max)
+		return -EOVERFLOW;
+
+	sem->u.sem.count = sum;
+	return 0;
+}
+
+static int ntsync_sem_post(struct ntsync_obj *sem, void __user *argp)
+{
+	__u32 __user *user_args = argp;
+	__u32 prev_count;
+	__u32 args;
+	int ret;
+
+	if (copy_from_user(&args, argp, sizeof(args)))
+		return -EFAULT;
+
+	if (sem->type != NTSYNC_TYPE_SEM)
+		return -EINVAL;
+
+	spin_lock(&sem->lock);
+
+	prev_count = sem->u.sem.count;
+	ret = post_sem_state(sem, args);
+
+	spin_unlock(&sem->lock);
+
+	if (!ret && put_user(prev_count, user_args))
+		ret = -EFAULT;
+
+	return ret;
+}
+
+static int ntsync_obj_release(struct inode *inode, struct file *file)
+{
+	struct ntsync_obj *obj = file->private_data;
+
+	fput(obj->dev->file);
+	kfree(obj);
+
+	return 0;
+}
+
+static long ntsync_obj_ioctl(struct file *file, unsigned int cmd,
+			     unsigned long parm)
+{
+	struct ntsync_obj *obj = file->private_data;
+	void __user *argp = (void __user *)parm;
+
+	switch (cmd) {
+	case NTSYNC_IOC_SEM_POST:
+		return ntsync_sem_post(obj, argp);
+	default:
+		return -ENOIOCTLCMD;
+	}
+}
+
+static const struct file_operations ntsync_obj_fops = {
+	.owner		= THIS_MODULE,
+	.release	= ntsync_obj_release,
+	.unlocked_ioctl	= ntsync_obj_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+	.llseek		= no_llseek,
+};
+
+static struct ntsync_obj *ntsync_alloc_obj(struct ntsync_device *dev,
+					   enum ntsync_type type)
+{
+	struct ntsync_obj *obj;
+
+	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
+	if (!obj)
+		return NULL;
+	obj->type = type;
+	obj->dev = dev;
+	get_file(dev->file);
+	spin_lock_init(&obj->lock);
+
+	return obj;
+}
+
+static int ntsync_obj_get_fd(struct ntsync_obj *obj)
+{
+	struct file *file;
+	int fd;
+
+	fd = get_unused_fd_flags(O_CLOEXEC);
+	if (fd < 0)
+		return fd;
+	file = anon_inode_getfile("ntsync", &ntsync_obj_fops, obj, O_RDWR);
+	if (IS_ERR(file)) {
+		put_unused_fd(fd);
+		return PTR_ERR(file);
+	}
+	obj->file = file;
+	fd_install(fd, file);
+
+	return fd;
+}
+
+static int ntsync_create_sem(struct ntsync_device *dev, void __user *argp)
+{
+	struct ntsync_sem_args __user *user_args = argp;
+	struct ntsync_sem_args args;
+	struct ntsync_obj *sem;
+	int fd;
+
+	if (copy_from_user(&args, argp, sizeof(args)))
+		return -EFAULT;
+
+	if (args.count > args.max)
+		return -EINVAL;
+
+	sem = ntsync_alloc_obj(dev, NTSYNC_TYPE_SEM);
+	if (!sem)
+		return -ENOMEM;
+	sem->u.sem.count = args.count;
+	sem->u.sem.max = args.max;
+	fd = ntsync_obj_get_fd(sem);
+	if (fd < 0) {
+		kfree(sem);
+		return fd;
+	}
+
+	return put_user(fd, &user_args->sem);
+}
+
+static int ntsync_char_open(struct inode *inode, struct file *file)
+{
+	struct ntsync_device *dev;
+
+	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev)
+		return -ENOMEM;
+
+	file->private_data = dev;
+	dev->file = file;
+	return nonseekable_open(inode, file);
+}
+
+static int ntsync_char_release(struct inode *inode, struct file *file)
+{
+	struct ntsync_device *dev = file->private_data;
+
+	kfree(dev);
+
+	return 0;
+}
+
+static long ntsync_char_ioctl(struct file *file, unsigned int cmd,
+			      unsigned long parm)
+{
+	struct ntsync_device *dev = file->private_data;
+	void __user *argp = (void __user *)parm;
+
+	switch (cmd) {
+	case NTSYNC_IOC_CREATE_SEM:
+		return ntsync_create_sem(dev, argp);
+	default:
+		return -ENOIOCTLCMD;
+	}
+}
+
+static const struct file_operations ntsync_fops = {
+	.owner		= THIS_MODULE,
+	.open		= ntsync_char_open,
+	.release	= ntsync_char_release,
+	.unlocked_ioctl	= ntsync_char_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+	.llseek		= no_llseek,
+};
+
+static struct miscdevice ntsync_misc = {
+	.minor		= MISC_DYNAMIC_MINOR,
+	.name		= NTSYNC_NAME,
+	.fops		= &ntsync_fops,
+};
+
+module_misc_device(ntsync_misc);
+
+MODULE_AUTHOR("Elizabeth Figura <zfigura@codeweavers.com>");
+MODULE_DESCRIPTION("Kernel driver for NT synchronization primitives");
+MODULE_LICENSE("GPL");