tpm: add support for partial reads

Currently to read a response from the TPM device an application needs
provide big enough buffer for the whole response and read it in one go.
The application doesn't know how big the response it beforehand so it
always needs to maintain a 4K buffer and read the max (4K).
In case if the user of the TSS library doesn't provide big enough
buffer the TCTI spec says that the library should set the required
size and return TSS2_TCTI_RC_INSUFFICIENT_BUFFER error code so that the
application could allocate a bigger buffer and call receive again.
To make it possible in the TSS library, this requires being able to do
partial reads from the driver.
The library would read the 10 bytes header first to get the actual size
of the response from the header, and then read the rest of the response.

This patch adds support for partial reads, i.e. the user can read the
response in one or multiple reads, until the whole response is consumed.
The user can also read only part of the response and ignore
the rest by issuing a new write to send a new command.

Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

drivers/char/tpm/tpm-dev-common.c

@@ -40,7 +40,7 @@ static void tpm_async_work(struct work_struct *work)
 
 	tpm_put_ops(priv->chip);
 	if (ret > 0) {
-		priv->data_pending = ret;
+		priv->response_length = ret;
 		mod_timer(&priv->user_read_timer, jiffies + (120 * HZ));
 	}
 	mutex_unlock(&priv->buffer_mutex);
@@ -63,7 +63,8 @@ static void tpm_timeout_work(struct work_struct *work)
 					      timeout_work);
 
 	mutex_lock(&priv->buffer_mutex);
-	priv->data_pending = 0;
+	priv->response_read = true;
+	priv->response_length = 0;
 	memset(priv->data_buffer, 0, sizeof(priv->data_buffer));
 	mutex_unlock(&priv->buffer_mutex);
 	wake_up_interruptible(&priv->async_wait);
@@ -74,6 +75,7 @@ void tpm_common_open(struct file *file, struct tpm_chip *chip,
 {
 	priv->chip = chip;
 	priv->space = space;
+	priv->response_read = true;
 
 	mutex_init(&priv->buffer_mutex);
 	timer_setup(&priv->user_read_timer, user_reader_timeout, 0);
@@ -90,22 +92,35 @@ ssize_t tpm_common_read(struct file *file, char __user *buf,
 	ssize_t ret_size = 0;
 	int rc;
 
-	del_singleshot_timer_sync(&priv->user_read_timer);
-	flush_work(&priv->timeout_work);
 	mutex_lock(&priv->buffer_mutex);
 
-	if (priv->data_pending) {
-		ret_size = min_t(ssize_t, size, priv->data_pending);
-		if (ret_size > 0) {
-			rc = copy_to_user(buf, priv->data_buffer, ret_size);
-			memset(priv->data_buffer, 0, priv->data_pending);
-			if (rc)
-				ret_size = -EFAULT;
+	if (priv->response_length) {
+		priv->response_read = true;
+
+		ret_size = min_t(ssize_t, size, priv->response_length);
+		if (!ret_size) {
+			priv->response_length = 0;
+			goto out;
 		}
 
-		priv->data_pending = 0;
+		rc = copy_to_user(buf, priv->data_buffer + *off, ret_size);
+		if (rc) {
+			memset(priv->data_buffer, 0, TPM_BUFSIZE);
+			priv->response_length = 0;
+			ret_size = -EFAULT;
+		} else {
+			memset(priv->data_buffer + *off, 0, ret_size);
+			priv->response_length -= ret_size;
+			*off += ret_size;
+		}
 	}
 
+out:
+	if (!priv->response_length) {
+		*off = 0;
+		del_singleshot_timer_sync(&priv->user_read_timer);
+		flush_work(&priv->timeout_work);
+	}
 	mutex_unlock(&priv->buffer_mutex);
 	return ret_size;
 }
@@ -125,7 +140,8 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf,
 	 * tpm_read or a user_read_timer timeout. This also prevents split
 	 * buffered writes from blocking here.
 	 */
-	if (priv->data_pending != 0 || priv->command_enqueued) {
+	if ((!priv->response_read && priv->response_length) ||
+	    priv->command_enqueued) {
 		ret = -EBUSY;
 		goto out;
 	}
@@ -150,6 +166,10 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf,
 		goto out;
 	}
 
+	priv->response_length = 0;
+	priv->response_read = false;
+	*off = 0;
+
 	/*
 	 * If in nonblocking mode schedule an async job to send
 	 * the command return the size.
@@ -168,7 +188,7 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf,
 	tpm_put_ops(priv->chip);
 
 	if (ret > 0) {
-		priv->data_pending = ret;
+		priv->response_length = ret;
 		mod_timer(&priv->user_read_timer, jiffies + (120 * HZ));
 		ret = size;
 	}
@@ -184,7 +204,7 @@ __poll_t tpm_common_poll(struct file *file, poll_table *wait)
 
 	poll_wait(file, &priv->async_wait, wait);
 
-	if (priv->data_pending)
+	if (!priv->response_read || priv->response_length)
 		mask = EPOLLIN | EPOLLRDNORM;
 	else
 		mask = EPOLLOUT | EPOLLWRNORM;
@@ -201,7 +221,7 @@ void tpm_common_release(struct file *file, struct file_priv *priv)
 	del_singleshot_timer_sync(&priv->user_read_timer);
 	flush_work(&priv->timeout_work);
 	file->private_data = NULL;
-	priv->data_pending = 0;
+	priv->response_length = 0;
 }
 
 int __init tpm_dev_common_init(void)

drivers/char/tpm/tpm-dev.h

@@ -9,14 +9,13 @@ struct file_priv {
 	struct tpm_chip *chip;
 	struct tpm_space *space;
 
-	/* Holds the amount of data passed or an error code from async op */
-	ssize_t data_pending;
 	struct mutex buffer_mutex;
-
 	struct timer_list user_read_timer;      /* user needs to claim result */
 	struct work_struct timeout_work;
 	struct work_struct async_work;
 	wait_queue_head_t async_wait;
+	size_t response_length;
+	bool response_read;
 	bool command_enqueued;
 
 	u8 data_buffer[TPM_BUFSIZE];