drm/amdkfd: Improve kfd_process lookup in kfd_ioctl

Use filep->private_data to store a pointer to the kfd_process data
structure. Take an extra reference for that, which gets released in
the kfd_release callback. Check that the process calling kfd_ioctl
is the same that opened the file descriptor. Return -EBADF if it's
not, so that this error can be distinguished in user mode.
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_chardev.c

@@ -42,6 +42,7 @@
 
 static long kfd_ioctl(struct file *, unsigned int, unsigned long);
 static int kfd_open(struct inode *, struct file *);
+static int kfd_release(struct inode *, struct file *);
 static int kfd_mmap(struct file *, struct vm_area_struct *);
 
 static const char kfd_dev_name[] = "kfd";
@@ -51,6 +52,7 @@ static const struct file_operations kfd_fops = {
 	.unlocked_ioctl = kfd_ioctl,
 	.compat_ioctl = compat_ptr_ioctl,
 	.open = kfd_open,
+	.release = kfd_release,
 	.mmap = kfd_mmap,
 };
 
@@ -124,8 +126,13 @@ static int kfd_open(struct inode *inode, struct file *filep)
 	if (IS_ERR(process))
 		return PTR_ERR(process);
 
-	if (kfd_is_locked())
+	if (kfd_is_locked()) {
+		kfd_unref_process(process);
 		return -EAGAIN;
+	}
+
+	/* filep now owns the reference returned by kfd_create_process */
+	filep->private_data = process;
 
 	dev_dbg(kfd_device, "process %d opened, compat mode (32 bit) - %d\n",
 		process->pasid, process->is_32bit_user_mode);
@@ -133,6 +140,16 @@ static int kfd_open(struct inode *inode, struct file *filep)
 	return 0;
 }
 
+static int kfd_release(struct inode *inode, struct file *filep)
+{
+	struct kfd_process *process = filep->private_data;
+
+	if (process)
+		kfd_unref_process(process);
+
+	return 0;
+}
+
 static int kfd_ioctl_get_version(struct file *filep, struct kfd_process *p,
 					void *data)
 {
@@ -1801,9 +1818,14 @@ static long kfd_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 
 	dev_dbg(kfd_device, "ioctl cmd 0x%x (#0x%x), arg 0x%lx\n", cmd, nr, arg);
 
-	process = kfd_get_process(current);
-	if (IS_ERR(process)) {
-		dev_dbg(kfd_device, "no process\n");
+	/* Get the process struct from the filep. Only the process
+	 * that opened /dev/kfd can use the file descriptor. Child
+	 * processes need to create their own KFD device context.
+	 */
+	process = filep->private_data;
+	if (process->lead_thread != current->group_leader) {
+		dev_dbg(kfd_device, "Using KFD FD in wrong process\n");
+		retcode = -EBADF;
 		goto err_i1;
 	}
 

drivers/gpu/drm/amd/amdkfd/kfd_process.c

@@ -324,6 +324,8 @@ struct kfd_process *kfd_create_process(struct file *filep)
 					(int)process->lead_thread->pid);
 	}
 out:
+	if (!IS_ERR(process))
+		kref_get(&process->ref);
 	mutex_unlock(&kfd_processes_mutex);
 
 	return process;