248 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/*3 * ntsync.c - Kernel driver for NT synchronization primitives4 *5 * Copyright (C) 2024 Elizabeth Figura <zfigura@codeweavers.com>6 */7 8#include <linux/anon_inodes.h>9#include <linux/file.h>10#include <linux/fs.h>11#include <linux/miscdevice.h>12#include <linux/module.h>13#include <linux/overflow.h>14#include <linux/slab.h>15#include <linux/spinlock.h>16#include <uapi/linux/ntsync.h>17 18#define NTSYNC_NAME "ntsync"19 20enum ntsync_type {21 NTSYNC_TYPE_SEM,22};23 24/*25 * Individual synchronization primitives are represented by26 * struct ntsync_obj, and each primitive is backed by a file.27 *28 * The whole namespace is represented by a struct ntsync_device also29 * backed by a file.30 *31 * Both rely on struct file for reference counting. Individual32 * ntsync_obj objects take a reference to the device when created.33 */34 35struct ntsync_obj {36 spinlock_t lock;37 38 enum ntsync_type type;39 40 struct file *file;41 struct ntsync_device *dev;42 43 /* The following fields are protected by the object lock. */44 union {45 struct {46 __u32 count;47 __u32 max;48 } sem;49 } u;50};51 52struct ntsync_device {53 struct file *file;54};55 56/*57 * Actually change the semaphore state, returning -EOVERFLOW if it is made58 * invalid.59 */60static int post_sem_state(struct ntsync_obj *sem, __u32 count)61{62 __u32 sum;63 64 lockdep_assert_held(&sem->lock);65 66 if (check_add_overflow(sem->u.sem.count, count, &sum) ||67 sum > sem->u.sem.max)68 return -EOVERFLOW;69 70 sem->u.sem.count = sum;71 return 0;72}73 74static int ntsync_sem_post(struct ntsync_obj *sem, void __user *argp)75{76 __u32 __user *user_args = argp;77 __u32 prev_count;78 __u32 args;79 int ret;80 81 if (copy_from_user(&args, argp, sizeof(args)))82 return -EFAULT;83 84 if (sem->type != NTSYNC_TYPE_SEM)85 return -EINVAL;86 87 spin_lock(&sem->lock);88 89 prev_count = sem->u.sem.count;90 ret = post_sem_state(sem, args);91 92 spin_unlock(&sem->lock);93 94 if (!ret && put_user(prev_count, user_args))95 ret = -EFAULT;96 97 return ret;98}99 100static int ntsync_obj_release(struct inode *inode, struct file *file)101{102 struct ntsync_obj *obj = file->private_data;103 104 fput(obj->dev->file);105 kfree(obj);106 107 return 0;108}109 110static long ntsync_obj_ioctl(struct file *file, unsigned int cmd,111 unsigned long parm)112{113 struct ntsync_obj *obj = file->private_data;114 void __user *argp = (void __user *)parm;115 116 switch (cmd) {117 case NTSYNC_IOC_SEM_POST:118 return ntsync_sem_post(obj, argp);119 default:120 return -ENOIOCTLCMD;121 }122}123 124static const struct file_operations ntsync_obj_fops = {125 .owner = THIS_MODULE,126 .release = ntsync_obj_release,127 .unlocked_ioctl = ntsync_obj_ioctl,128 .compat_ioctl = compat_ptr_ioctl,129};130 131static struct ntsync_obj *ntsync_alloc_obj(struct ntsync_device *dev,132 enum ntsync_type type)133{134 struct ntsync_obj *obj;135 136 obj = kzalloc(sizeof(*obj), GFP_KERNEL);137 if (!obj)138 return NULL;139 obj->type = type;140 obj->dev = dev;141 get_file(dev->file);142 spin_lock_init(&obj->lock);143 144 return obj;145}146 147static int ntsync_obj_get_fd(struct ntsync_obj *obj)148{149 struct file *file;150 int fd;151 152 fd = get_unused_fd_flags(O_CLOEXEC);153 if (fd < 0)154 return fd;155 file = anon_inode_getfile("ntsync", &ntsync_obj_fops, obj, O_RDWR);156 if (IS_ERR(file)) {157 put_unused_fd(fd);158 return PTR_ERR(file);159 }160 obj->file = file;161 fd_install(fd, file);162 163 return fd;164}165 166static int ntsync_create_sem(struct ntsync_device *dev, void __user *argp)167{168 struct ntsync_sem_args __user *user_args = argp;169 struct ntsync_sem_args args;170 struct ntsync_obj *sem;171 int fd;172 173 if (copy_from_user(&args, argp, sizeof(args)))174 return -EFAULT;175 176 if (args.count > args.max)177 return -EINVAL;178 179 sem = ntsync_alloc_obj(dev, NTSYNC_TYPE_SEM);180 if (!sem)181 return -ENOMEM;182 sem->u.sem.count = args.count;183 sem->u.sem.max = args.max;184 fd = ntsync_obj_get_fd(sem);185 if (fd < 0) {186 kfree(sem);187 return fd;188 }189 190 return put_user(fd, &user_args->sem);191}192 193static int ntsync_char_open(struct inode *inode, struct file *file)194{195 struct ntsync_device *dev;196 197 dev = kzalloc(sizeof(*dev), GFP_KERNEL);198 if (!dev)199 return -ENOMEM;200 201 file->private_data = dev;202 dev->file = file;203 return nonseekable_open(inode, file);204}205 206static int ntsync_char_release(struct inode *inode, struct file *file)207{208 struct ntsync_device *dev = file->private_data;209 210 kfree(dev);211 212 return 0;213}214 215static long ntsync_char_ioctl(struct file *file, unsigned int cmd,216 unsigned long parm)217{218 struct ntsync_device *dev = file->private_data;219 void __user *argp = (void __user *)parm;220 221 switch (cmd) {222 case NTSYNC_IOC_CREATE_SEM:223 return ntsync_create_sem(dev, argp);224 default:225 return -ENOIOCTLCMD;226 }227}228 229static const struct file_operations ntsync_fops = {230 .owner = THIS_MODULE,231 .open = ntsync_char_open,232 .release = ntsync_char_release,233 .unlocked_ioctl = ntsync_char_ioctl,234 .compat_ioctl = compat_ptr_ioctl,235};236 237static struct miscdevice ntsync_misc = {238 .minor = MISC_DYNAMIC_MINOR,239 .name = NTSYNC_NAME,240 .fops = &ntsync_fops,241};242 243module_misc_device(ntsync_misc);244 245MODULE_AUTHOR("Elizabeth Figura <zfigura@codeweavers.com>");246MODULE_DESCRIPTION("Kernel driver for NT synchronization primitives");247MODULE_LICENSE("GPL");248