RE: [PATCH v10 1/1] Add support for IPMB driver

[Asmaa Mnebhi]

Hi Corey,

Thank you for your comments. Please see inline response. I will be posting a new patch shortly.

-----Original Message-----
From: Corey Minyard <tcminyard@xxxxxxxxx> On Behalf Of Corey Minyard
Sent: Wednesday, June 5, 2019 7:53 PM
To: Asmaa Mnebhi <Asmaa@xxxxxxxxxxxx>
Cc: wsa@xxxxxxxxxxxxx; Vadim Pasternak <vadimp@xxxxxxxxxxxx>; Michael Shych <michaelsh@xxxxxxxxxxxx>; rdunlap@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-i2c@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v10 1/1] Add support for IPMB driver

On Wed, Jun 05, 2019 at 03:09:30PM -0400, Asmaa Mnebhi wrote:
> Support receiving IPMB requests on a Satellite MC from the BMC.
> Once a response is ready, this driver will send back a response to the 
> BMC via the IPMB channel.

A lot of comments inline.

-corey

SNIP...
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * IPMB driver to receive a request and send a response
> + *
> + * Copyright (C) 2018 Mellanox Techologies, Ltd.
> + *
> + * This was inspired by Brendan Higgins' ipmi-bmc-bt-i2c driver.
> + */
> +
> +#include <linux/acpi.h>
> +#include <linux/errno.h>
> +#include <linux/i2c.h>
> +#include <linux/miscdevice.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/poll.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/wait.h>
> +
> +#define MAX_MSG_LEN		128
> +#define IPMB_REQUEST_LEN_MIN	7
> +#define NETFN_RSP_BIT_MASK	0x4
> +#define REQUEST_QUEUE_MAX_LEN	256
> +
> +#define IPMB_MSG_LEN_IDX	0
> +#define RQ_SA_8BIT_IDX		1
> +#define NETFN_LUN_IDX		2
> +
> +/* get 7-bit address from 8-bit address */
> +#define GET_7BIT_ADDR(addr)	(addr >> 1)
> +
> +#define IPMB_MSG_PAYLOAD_LEN_MAX (MAX_MSG_LEN - IPMB_REQUEST_LEN_MIN 
> +- 1)
> +
> +#define SMBUS_MSG_HEADER_LENGTH	2
> +#define SMBUS_MSG_IDX_OFFSET	(SMBUS_MSG_HEADER_LENGTH + 1)
> +
> +#define GET_8BIT_ADDR(addr_7bit) ((addr_7bit << 1) & 0xff)
> +
> +#define UNPOPULATED_RQ_SA	0xff
> +
> +/* Reference 7-bit rq_sa */
> +static u8 reference_rq_sa[128];
> +
> +struct ipmb_msg {
> +	u8 len;
> +	u8 rs_sa;
> +	u8 netfn_rs_lun;
> +	u8 checksum1;
> +	u8 rq_sa;
> +	u8 rq_seq_rq_lun;
> +	u8 cmd;
> +	u8 payload[IPMB_MSG_PAYLOAD_LEN_MAX];
> +	/* checksum2 is included in payload */ } __packed;
> +
> +struct ipmb_request_elem {
> +	struct list_head list;
> +	struct ipmb_msg request;
> +};
> +
> +struct ipmb_dev {
> +	struct i2c_client *client;
> +	struct miscdevice miscdev;
> +	struct ipmb_msg request;
> +	struct list_head request_queue;
> +	atomic_t request_queue_len;
> +	size_t msg_idx;
> +	spinlock_t lock;
> +	wait_queue_head_t wait_queue;
> +	struct mutex file_mutex;
> +};
> +
> +static int receive_ipmb_request(struct ipmb_dev *ipmb_dev,
> +				bool non_blocking,
> +				struct ipmb_msg *ipmb_request)
> +{
> +	struct ipmb_request_elem *queue_elem;
> +	unsigned long flags;
> +	int res;
> +
> +	while (!atomic_read(&ipmb_dev->request_queue_len)) {
> +		if (non_blocking)
> +			return -EAGAIN;
> +
> +		res = wait_event_interruptible(ipmb_dev->wait_queue,
> +				atomic_read(&ipmb_dev->request_queue_len));
> +		if (res)
> +			return res;
> +
> +	}
> +

This can only be called from user context with interrupts on,
spin_lock_irq() is ok here.

Done.

> +	spin_lock_irqsave(&ipmb_dev->lock, flags);
> +
> +	if (list_empty(&ipmb_dev->request_queue)) {
> +		spin_unlock_irqrestore(&ipmb_dev->lock, flags);
> +		dev_err(&ipmb_dev->client->dev, "request_queue is empty\n");
> +		return -EIO;
> +	}
> +
> +	queue_elem = list_first_entry(&ipmb_dev->request_queue,
> +					struct ipmb_request_elem, list);
> +	memcpy(ipmb_request, &queue_elem->request, sizeof(*ipmb_request));
> +	list_del(&queue_elem->list);
> +	kfree(queue_elem);
> +	atomic_dec(&ipmb_dev->request_queue_len);
> +
> +	spin_unlock_irqrestore(&ipmb_dev->lock, flags);
> +
> +	return 0;
> +}
> +
> +static inline struct ipmb_dev *to_ipmb_dev(struct file *file) {
> +	return container_of(file->private_data, struct ipmb_dev, miscdev); }
> +
> +static ssize_t ipmb_read(struct file *file, char __user *buf, size_t count,
> +			loff_t *ppos)
> +{
> +	struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
> +	struct ipmb_msg msg;
> +	ssize_t ret;
> +	int bus;
> +
> +	memset(&msg, 0, sizeof(msg));
> +

The mutex below is not interruptable, so if the task is interrupted, it could be blocked here.

This function and receive_ipmb_request() seem more complicated than required I don't think you need file mutex or request_queue_len.

Something like:
	spin_lock_irq();
	while (list_empty(&ipmb_dev->request_queue)) {
		spin_unlock_irq();
		if (file->f_flags & O_NONBLOCK)
			return -EAGAIN;
		res = wait_event_interruptible(ipmb_dev->wait_queue,
				!list_empty(&ipmb_dev->request_queue));
		if (res)
			return res;
		spin_lock_irq();
	}
	queue_elem = list_first_entry(&ipmb_dev->request_queue,
				      struct ipmb_request_elem, list);
	spin_unlock_irq();
	...

Done.

> +	mutex_lock(&ipmb_dev->file_mutex);
> +	ret = receive_ipmb_request(ipmb_dev, file->f_flags & O_NONBLOCK,
> +				&msg);
> +	if (ret < 0)
> +		goto out;
> +
> +	bus = ipmb_dev->client->adapter->nr;

You are using bus here without checking the range.

I still don't understandy why you are checking this, anyway.  IMHO there is no value in this check, just do what userland tells you to do.  It seems restrictive, you have to receive a message from the remote end to respond to it.  How do you send an unsolicited event?  There are systems with multiple managment controllers that can send messages to other management controllers (ATCA).

I agree with you in the sense that the user program "should be" reliable since it verifies the sanity of the message via the checksum and it might be ok for the driver to rely on it. But I think Wolfram's concern was that the linux driver is "too" reliable on the sanity of the response passed by userland. It is irrelevant  to check all other IPMB message bytes passed by the user program since it is the role of the BMC (requester) to do so once it has received the response. However, it is relevant to verify that the rq_sa is correct for the one reason that we pass it to i2c_smbus_write_block_data to send the data back to the requester.
Here are 2 possible scenarios if the user program sends a corrupted rq_sa (i.e. a rq_sa that is different from the requester's) to this driver:
	a) If there is no slave device associated with that address, i2c_smbus_write_block_data function would just fail, which is the expected behavior. No issues here. It is  also fairly easy to debug.
	b) if there is a slave device associated with that address, then we might be sending unwanted data to that device. So this could be an issue.


> +	if (reference_rq_sa[bus] == UNPOPULATED_RQ_SA)
> +		reference_rq_sa[bus] = GET_7BIT_ADDR(msg.rq_sa);
> +
> +	count = min_t(size_t, count, msg.len + 1);
> +	if (copy_to_user(buf, &msg, count)) {
> +		ret = -EFAULT;
> +		goto out;
> +	}
> +
> +out:
> +	mutex_unlock(&ipmb_dev->file_mutex);
> +	return ret < 0 ? ret : count;
> +}
> +
> +static ssize_t ipmb_write(struct file *file, const char __user *buf,
> +			size_t count, loff_t *ppos)
> +{
> +	struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
> +	u8 rq_sa, netf_rq_lun, msg_len;
> +	struct i2c_client rq_client;
> +	u8 msg[MAX_MSG_LEN];
> +	ssize_t ret;
> +	int bus;
> +
> +	if (count > sizeof(msg))
> +		return -EINVAL;
> +
> +	if (copy_from_user(&msg, buf, count) || count < msg[0])
> +		return -EFAULT;

Minor nit - you are returning EFAULT if count < msg[0].

Done.

> +
> +	bus = ipmb_dev->client->adapter->nr;
> +	rq_sa = GET_7BIT_ADDR(msg[RQ_SA_8BIT_IDX]);
> +	if (rq_sa != reference_rq_sa[bus])
> +		return -EINVAL;
> +
> +	netf_rq_lun = msg[NETFN_LUN_IDX];
> +	/*
> +	 * subtract rq_sa and netf_rq_lun from the length of the msg passed to
> +	 * i2c_smbus_write_block_data_local
> +	 */
> +	msg_len = msg[IPMB_MSG_LEN_IDX] - SMBUS_MSG_HEADER_LENGTH;
> +
> +	strcpy(rq_client.name, "ipmb_requester");
> +	rq_client.adapter = ipmb_dev->client->adapter;
> +	rq_client.flags = ipmb_dev->client->flags;
> +	rq_client.addr = rq_sa;
> +

Why do you need a mutex below?

Removed.

> +	mutex_lock(&ipmb_dev->file_mutex);
> +	ret = i2c_smbus_write_block_data(&rq_client, netf_rq_lun, msg_len,
> +					msg + SMBUS_MSG_IDX_OFFSET);
> +	mutex_unlock(&ipmb_dev->file_mutex);
> +
> +	return ret ? : count;
> +}
> +
> +static unsigned int ipmb_poll(struct file *file, poll_table *wait) {
> +	struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
> +	unsigned int mask = POLLOUT;
> +
> +	mutex_lock(&ipmb_dev->file_mutex);
> +	poll_wait(file, &ipmb_dev->wait_queue, wait);
> +
> +	if (atomic_read(&ipmb_dev->request_queue_len))
> +		mask |= POLLIN;
> +	mutex_unlock(&ipmb_dev->file_mutex);
> +
> +	return mask;
> +}
> +
> +static const struct file_operations ipmb_fops = {
> +	.owner	= THIS_MODULE,
> +	.read	= ipmb_read,
> +	.write	= ipmb_write,
> +	.poll	= ipmb_poll,
> +};
> +
> +/* Called with ipmb_dev->lock held. */ static void 
> +ipmb_handle_request(struct ipmb_dev *ipmb_dev) {
> +	struct ipmb_request_elem *queue_elem;
> +
> +	if (atomic_read(&ipmb_dev->request_queue_len) >=
> +			REQUEST_QUEUE_MAX_LEN)
> +		return;
> +

If this is really called from interrupt context or with preempt disabled, you can't use GFP_KERNEL.

I am changing it to GFP_ATOMIC

> +	queue_elem = kmalloc(sizeof(*queue_elem), GFP_KERNEL);
> +	if (!queue_elem)
> +		return;
> +
> +	memcpy(&queue_elem->request, &ipmb_dev->request,
> +		sizeof(struct ipmb_msg));
> +	list_add(&queue_elem->list, &ipmb_dev->request_queue);
> +	atomic_inc(&ipmb_dev->request_queue_len);
> +	wake_up_all(&ipmb_dev->wait_queue);
> +}
> +
> +static u8 ipmb_verify_checksum1(struct ipmb_dev *ipmb_dev, u8 rs_sa) 
> +{
> +	/* The 8 lsb of the sum is 0 when the checksum is valid */
> +	return (rs_sa + ipmb_dev->request.netfn_rs_lun +
> +		ipmb_dev->request.checksum1);
> +}
> +
> +static bool is_ipmb_request(struct ipmb_dev *ipmb_dev, u8 rs_sa) {
> +	if (ipmb_dev->msg_idx >= IPMB_REQUEST_LEN_MIN) {
> +		if (ipmb_verify_checksum1(ipmb_dev, rs_sa))
> +			return false;
> +
> +		/*
> +		 * Check whether this is an IPMB request or
> +		 * response.
> +		 * The 6 MSB of netfn_rs_lun are dedicated to the netfn
> +		 * while the remaining bits are dedicated to the lun.
> +		 * If the LSB of the netfn is cleared, it is associated
> +		 * with an IPMB request.
> +		 * If the LSB of the netfn is set, it is associated with
> +		 * an IPMB response.
> +		 */
> +		if (!(ipmb_dev->request.netfn_rs_lun & NETFN_RSP_BIT_MASK))
> +			return true;
> +	}
> +	return false;
> +}
> +
> +/*
> + * The IPMB protocol only supports I2C Writes so there is no need
> + * to support I2C_SLAVE_READ* events.
> + * This i2c callback function only monitors IPMB request messages
> + * and adds them in a queue, so that they can be handled by
> + * receive_ipmb_request.
> + */
> +static int ipmb_slave_cb(struct i2c_client *client,
> +			enum i2c_slave_event event, u8 *val) {
> +	struct ipmb_dev *ipmb_dev = i2c_get_clientdata(client);
> +	u8 *buf = (u8 *)&ipmb_dev->request;
> +
> +	spin_lock(&ipmb_dev->lock);

Are you sure this is called with interrupts off?

If it's called from user context, then you can just use a mutex.  If not, I think you need spin_lock_irqsave() here.

I am changing it to spin_lock_irqsave

> +	switch (event) {
> +	case I2C_SLAVE_WRITE_REQUESTED:
> +		memset(&ipmb_dev->request, 0, sizeof(ipmb_dev->request));
> +		ipmb_dev->msg_idx = 0;
> +
> +		/*
> +		 * At index 0, ipmb_msg stores the length of msg,
> +		 * skip it for now.
> +		 * The len will be populated once the whole
> +		 * buf is populated.
> +		 *
> +		 * The I2C bus driver's responsibility is to pass the
> +		 * data bytes to the backend driver; it does not
> +		 * forward the i2c slave address.
> +		 * Since the first byte in the IPMB message is the
> +		 * address of the responder, it is the responsibility
> +		 * of the IPMB driver to format the message properly.
> +		 * So this driver prepends the address of the responder
> +		 * to the received i2c data before the request message
> +		 * is handled in userland.
> +		 */
> +		buf[++ipmb_dev->msg_idx] = GET_8BIT_ADDR(client->addr);
> +		break;
> +
> +	case I2C_SLAVE_WRITE_RECEIVED:
> +		if (ipmb_dev->msg_idx >= sizeof(struct ipmb_msg))
> +			break;
> +
> +		buf[++ipmb_dev->msg_idx] = *val;
> +		break;
> +
> +	case I2C_SLAVE_STOP:
> +		ipmb_dev->request.len = ipmb_dev->msg_idx;
> +
> +		if (is_ipmb_request(ipmb_dev, GET_8BIT_ADDR(client->addr)))
> +			ipmb_handle_request(ipmb_dev);
> +		break;
> +
> +	default:
> +		break;
> +	}
> +	spin_unlock(&ipmb_dev->lock);
> +
> +	return 0;
> +}
> +
> +static int ipmb_probe(struct i2c_client *client,
> +			const struct i2c_device_id *id)
> +{
> +	struct ipmb_dev *ipmb_dev;
> +	int ret;
> +
> +	ipmb_dev = devm_kzalloc(&client->dev, sizeof(*ipmb_dev),
> +					GFP_KERNEL);
> +	if (!ipmb_dev)
> +		return -ENOMEM;
> +
> +	spin_lock_init(&ipmb_dev->lock);
> +	init_waitqueue_head(&ipmb_dev->wait_queue);
> +	atomic_set(&ipmb_dev->request_queue_len, 0);
> +	INIT_LIST_HEAD(&ipmb_dev->request_queue);
> +
> +	mutex_init(&ipmb_dev->file_mutex);
> +
> +	ipmb_dev->miscdev.minor = MISC_DYNAMIC_MINOR;
> +
> +	ipmb_dev->miscdev.name = devm_kasprintf(&client->dev, GFP_KERNEL,
> +						"%s%d", "ipmb-",
> +						client->adapter->nr);
> +	ipmb_dev->miscdev.fops = &ipmb_fops;
> +	ipmb_dev->miscdev.parent = &client->dev;
> +	ret = misc_register(&ipmb_dev->miscdev);
> +	if (ret)
> +		return ret;
> +
> +	ipmb_dev->client = client;
> +	i2c_set_clientdata(client, ipmb_dev);
> +	ret = i2c_slave_register(client, ipmb_slave_cb);
> +	if (ret) {
> +		misc_deregister(&ipmb_dev->miscdev);
> +		return ret;
> +	}
> +
> +	reference_rq_sa[client->adapter->nr] = UNPOPULATED_RQ_SA;
> +
> +	return 0;
> +}
> +
> +static int ipmb_remove(struct i2c_client *client) {
> +	struct ipmb_dev *ipmb_dev = i2c_get_clientdata(client);
> +
> +	i2c_slave_unregister(client);
> +	misc_deregister(&ipmb_dev->miscdev);
> +
> +	return 0;
> +}
> +
> +static const struct i2c_device_id ipmb_id[] = {
> +	{ "ipmb-dev", 0 },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(i2c, ipmb_id);
> +
> +static const struct acpi_device_id acpi_ipmb_id[] = {
> +	{ "IPMB0001", 0 },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(acpi, acpi_ipmb_id);
> +
> +static struct i2c_driver ipmb_driver = {
> +	.driver = {
> +		.owner = THIS_MODULE,
> +		.name = "ipmb-dev",
> +		.acpi_match_table = ACPI_PTR(acpi_ipmb_id),
> +	},
> +	.probe = ipmb_probe,
> +	.remove = ipmb_remove,
> +	.id_table = ipmb_id,
> +};
> +module_i2c_driver(ipmb_driver);
> +
> +MODULE_AUTHOR("Mellanox Technologies"); MODULE_DESCRIPTION("IPMB 
> +driver"); MODULE_LICENSE("GPL v2");
> --
> 2.1.2
>