Message-ID: <20190610173900.GA5545@minyard.net>
Date:   Mon, 10 Jun 2019 12:39:00 -0500
From:   Corey Minyard <minyard@....org>
To:     Asmaa Mnebhi <Asmaa@...lanox.com>
Cc:     wsa@...-dreams.de, vadimp@...lanox.com, michaelsh@...lanox.com,
        rdunlap@...radead.org, linux-kernel@...r.kernel.org,
        linux-i2c@...r.kernel.org
Subject: Re: [PATCH v11 1/1] Add support for IPMB driver

On Mon, Jun 10, 2019 at 10:38:39AM -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.

I should have responded to you earlier email sooner.

On the reference_rq_sa[], thing, I just think it is a bad idea.
It means you can only ever respond to the first device that has
sent you a message.  There's nothing in the IPMI or IPMB spec
that has this requirement, and there are known systems out
there that don't work this way.

It may be that this saves things on the IPMB from arbitrarily
sending messages to other things on the IPMB, but that can still
happen in this case, it could just only send them to one place.
As long as the response bit is set, these messages really can't
be harmful, anyway.  And if you really wanted to go all the way
with the restriction, why not just not respond at all unless the
request was from 0x20?

Plus, the way it is implemented, it will still deliver the
message to userland, userland will process it, do a write, and
the write will fail.  That's really not a very good idea.

So I am against this implementation.

I would be ok with checking that the response bit is set in
writes.  That should provide plenty of protection against
arbitrary commands being issued through this interface, and
is in line with the specification.

-corey

> 
> Signed-off-by: Asmaa Mnebhi <Asmaa@...lanox.com>
> Acked-by: vadimp@...lanox.com
> ---
>  Documentation/IPMB.txt           | 103 +++++++++++
>  drivers/char/ipmi/Kconfig        |   8 +
>  drivers/char/ipmi/Makefile       |   1 +
>  drivers/char/ipmi/ipmb_dev_int.c | 383 +++++++++++++++++++++++++++++++++++++++
>  4 files changed, 495 insertions(+)
>  create mode 100644 Documentation/IPMB.txt
>  create mode 100644 drivers/char/ipmi/ipmb_dev_int.c
> 
> diff --git a/Documentation/IPMB.txt b/Documentation/IPMB.txt
> new file mode 100644
> index 0000000..7160d53
> --- /dev/null
> +++ b/Documentation/IPMB.txt
> @@ -0,0 +1,103 @@
> +==============================
> +IPMB Driver for a Satellite MC
> +==============================
> +
> +The Intelligent Platform Management Bus or IPMB, is an
> +I2C bus that provides a standardized interconnection between
> +different boards within a chassis. This interconnection is
> +between the baseboard management (BMC) and chassis electronics.
> +IPMB is also associated with the messaging protocol through the
> +IPMB bus.
> +
> +The devices using the IPMB are usually management
> +controllers that perform management functions such as servicing
> +the front panel interface, monitoring the baseboard,
> +hot-swapping disk drivers in the system chassis, etc...
> +
> +When an IPMB is implemented in the system, the BMC serves as
> +a controller to give system software access to the IPMB. The BMC
> +sends IPMI requests to a device (usually a Satellite Management
> +Controller or Satellite MC) via IPMB and the device
> +sends a response back to the BMC.
> +
> +For more information on IPMB and the format of an IPMB message,
> +refer to the IPMB and IPMI specifications.
> +
> +IPMB driver for Satellite MC
> +----------------------------
> +
> +ipmb-dev-int - This is the driver needed on a Satellite MC to
> +receive IPMB messages from a BMC and send a response back.
> +This driver works with the I2C driver and a userspace
> +program such as OpenIPMI:
> +
> +1) It is an I2C slave backend driver. So, it defines a callback
> +function to set the Satellite MC as an I2C slave.
> +This callback function handles the received IPMI requests.
> +
> +2) It defines the read and write functions to enable a user
> +space program (such as OpenIPMI) to communicate with the kernel.
> +
> +
> +Load the IPMB driver
> +--------------------
> +
> +The driver needs to be loaded at boot time or manually first.
> +First, make sure you have the following in your config file:
> +CONFIG_IPMB_DEVICE_INTERFACE=y
> +
> +1) If you want the driver to be loaded at boot time:
> +
> +a) Add this entry to your ACPI table, under the appropriate SMBus:
> +
> +Device (SMB0) // Example SMBus host controller
> +{
> +  Name (_HID, "<Vendor-Specific HID>") // Vendor-Specific HID
> +  Name (_UID, 0) // Unique ID of particular host controller
> +  :
> +  :
> +    Device (IPMB)
> +    {
> +      Name (_HID, "IPMB0001") // IPMB device interface
> +      Name (_UID, 0) // Unique device identifier
> +    }
> +}
> +
> +b) Example for device tree:
> +
> +&i2c2 {
> +         status = "okay";
> + 
> +         ipmb@10 {
> +                 compatible = "ipmb-dev";
> +                 reg = <0x10>;
> +         };
> +};
> +
> +2) Manually from Linux:
> +modprobe ipmb-dev-int
> +
> +
> +Instantiate the device
> +----------------------
> +
> +After loading the driver, you can instantiate the device as
> +described in 'Documentation/i2c/instantiating-devices'.
> +If you have multiple BMCs, each connected to your Satellite MC via
> +a different I2C bus, you can instantiate a device for each of
> +those BMCs.
> +The name of the instantiated device contains the I2C bus number
> +associated with it as follows:
> +
> +BMC1 ------ IPMB/I2C bus 1 ---------|   /dev/ipmb-1
> +				Satellite MC
> +BMC1 ------ IPMB/I2C bus 2 ---------|   /dev/ipmb-2
> +
> +For instance, you can instantiate the ipmb-dev-int device from
> +user space at the 7 bit address 0x10 on bus 2:
> +
> +  # echo ipmb-dev 0x1010 > /sys/bus/i2c/devices/i2c-2/new_device
> +
> +This will create the device file /dev/ipmb-2, which can be accessed
> +by the user space program. The device needs to be instantiated
> +before running the user space program.
> diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
> index caac5d2..811fccb 100644
> --- a/drivers/char/ipmi/Kconfig
> +++ b/drivers/char/ipmi/Kconfig
> @@ -75,6 +75,14 @@ config IPMI_SSIF
>  	 have a driver that must be accessed over an I2C bus instead of a
>  	 standard interface.  This module requires I2C support.
>  
> +config IPMB_DEVICE_INTERFACE
> +       tristate 'IPMB Interface handler'
> +       depends on I2C_SLAVE
> +       help
> +         Provides a driver for a device (Satellite MC) to
> +         receive requests and send responses back to the BMC via
> +         the IPMB interface. This module requires I2C support.
> +
>  config IPMI_POWERNV
>         depends on PPC_POWERNV
>         tristate 'POWERNV (OPAL firmware) IPMI interface'
> diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile
> index 3f06b20..0822adc 100644
> --- a/drivers/char/ipmi/Makefile
> +++ b/drivers/char/ipmi/Makefile
> @@ -26,3 +26,4 @@ obj-$(CONFIG_IPMI_KCS_BMC) += kcs_bmc.o
>  obj-$(CONFIG_ASPEED_BT_IPMI_BMC) += bt-bmc.o
>  obj-$(CONFIG_ASPEED_KCS_IPMI_BMC) += kcs_bmc_aspeed.o
>  obj-$(CONFIG_NPCM7XX_KCS_IPMI_BMC) += kcs_bmc_npcm7xx.o
> +obj-$(CONFIG_IPMB_DEVICE_INTERFACE) += ipmb_dev_int.o
> diff --git a/drivers/char/ipmi/ipmb_dev_int.c b/drivers/char/ipmi/ipmb_dev_int.c
> new file mode 100644
> index 0000000..7241206
> --- /dev/null
> +++ b/drivers/char/ipmi/ipmb_dev_int.c
> @@ -0,0 +1,383 @@
> +// 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
> +
> +#define GET_7BIT_ADDR(addr_8bit)	(addr_8bit >> 1)
> +#define GET_8BIT_ADDR(addr_7bit)	((addr_7bit << 1) & 0xff)
> +
> +#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
> +#define MAX_I2C_BUS		128
> +
> +/* Reference 7-bit rq_sa */
> +static u8 reference_rq_sa[MAX_I2C_BUS];
> +
> +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 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_request_elem *queue_elem;
> +	struct ipmb_msg msg;
> +	ssize_t ret;
> +	int bus;
> +
> +	memset(&msg, 0, sizeof(msg));
> +
> +	spin_lock_irq(&ipmb_dev->lock);
> +
> +	while (list_empty(&ipmb_dev->request_queue)) {
> +		spin_unlock_irq(&ipmb_dev->lock);
> +
> +		if (file->f_flags & O_NONBLOCK)
> +			return -EAGAIN;
> +
> +		ret = wait_event_interruptible(ipmb_dev->wait_queue,
> +				!list_empty(&ipmb_dev->request_queue));
> +		if (ret)
> +			return ret;
> +
> +		spin_lock_irq(&ipmb_dev->lock);
> +	}
> +
> +	queue_elem = list_first_entry(&ipmb_dev->request_queue,
> +					struct ipmb_request_elem, list);
> +	memcpy(&msg, &queue_elem->request, sizeof(msg));
> +	list_del(&queue_elem->list);
> +	kfree(queue_elem);
> +	atomic_dec(&ipmb_dev->request_queue_len);
> +
> +	spin_unlock_irq(&ipmb_dev->lock);
> +
> +	count = min_t(size_t, count, msg.len + 1);
> +	if (copy_to_user(buf, &msg, count))
> +		ret = -EFAULT;
> +
> +	bus = ipmb_dev->client->adapter->nr;
> +	if (bus >= MAX_I2C_BUS)
> +		ret = -EINVAL;
> +
> +	if (reference_rq_sa[bus] == UNPOPULATED_RQ_SA)
> +		reference_rq_sa[bus] = GET_7BIT_ADDR(msg.rq_sa);
> +
> +	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))
> +		return -EFAULT;
> +
> +	if (count < msg[0])
> +		return -EINVAL;
> +
> +	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;
> +
> +	ret = i2c_smbus_write_block_data(&rq_client, netf_rq_lun, msg_len,
> +					msg + SMBUS_MSG_IDX_OFFSET);
> +
> +	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;
> +
> +	queue_elem = kmalloc(sizeof(*queue_elem), GFP_ATOMIC);
> +	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;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&ipmb_dev->lock, flags);
> +	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_irqrestore(&ipmb_dev->lock, flags);
> +
> +	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
> 

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