Subject: Re: [PATCH V2 2/2] powerpc/powernv : Add support for OPAL-OCC command/response interface

From: Cyril Bur <[email-masked]>
Date: Wed, 14 Jun 2017 14:44:56 +1000

On Tue, 2017-06-13 at 23:26 +0530, Shilpasri G Bhat wrote:
> In P9, OCC (On-Chip-Controller) supports shared memory based
> commad-response interface. Within the shared memory there is an OPAL
> command buffer and OCC response buffer that can be used to send
> inband commands to OCC. This patch adds a platform driver to support
> the command/response interface between OCC and the host.
> 

Hi Shilpasri,

I have another question about printing of errors, see below. Otherwise
looks better.

When you're dropping the locks I wonder why you couldn't just use
atomic_set().

Finally, as you say below, if a user does a read() without having done
a write(), there isn't really any guarantee as to what they get. They
will get the previous response if there had been a write() call, what
about if there had never been a write() call? 
Could this be considered a security problem? Imagine that one program
is using the file descriptor and a malicious program keeps trying to
get the file descriptor and then the program which has the file
descriptor crashes? What information might the malicious program get?

More inline,

Cyril

> Signed-off-by: Shilpasri G Bhat <[email-masked]>
> ---
> Changes from V2:
> - Remove spinlock and use atomic_t for setting and clearing flags
> - Fix endian swapping
> - Use pa() and va() before and after opal call for accessing buffer
>   data
> - Replace (u8 *) with __be64 for buffer pointers
> - User reads the previous OCC response if the user does a read()
>   before a write(). Is this wrong?
> - Add WARN_ON check for nr_occs > 254
> 
>  arch/powerpc/include/asm/opal-api.h            |  41 +++-
>  arch/powerpc/include/asm/opal.h                |   3 +
>  arch/powerpc/platforms/powernv/Makefile        |   2 +-
>  arch/powerpc/platforms/powernv/opal-occ.c      | 314 +++++++++++++++++++++++++
>  arch/powerpc/platforms/powernv/opal-wrappers.S |   1 +
>  arch/powerpc/platforms/powernv/opal.c          |   8 +
>  6 files changed, 367 insertions(+), 2 deletions(-)
>  create mode 100644 arch/powerpc/platforms/powernv/opal-occ.c
> 
> diff --git a/arch/powerpc/include/asm/opal-api.h b/arch/powerpc/include/asm/opal-api.h
> index cb3e624..011d86c 100644
> --- a/arch/powerpc/include/asm/opal-api.h
> +++ b/arch/powerpc/include/asm/opal-api.h
> @@ -42,6 +42,10 @@
>  #define OPAL_I2C_STOP_ERR	-24
>  #define OPAL_XIVE_PROVISIONING	-31
>  #define OPAL_XIVE_FREE_ACTIVE	-32
> +#define OPAL_OCC_INVALID_STATE	-33
> +#define OPAL_OCC_BUSY		-34
> +#define OPAL_OCC_CMD_TIMEOUT	-35
> +#define OPAL_OCC_RSP_MISMATCH	-36
>  
>  /* API Tokens (in r0) */
>  #define OPAL_INVALID_CALL		       -1
> @@ -190,7 +194,8 @@
>  #define OPAL_NPU_INIT_CONTEXT			146
>  #define OPAL_NPU_DESTROY_CONTEXT		147
>  #define OPAL_NPU_MAP_LPAR			148
> -#define OPAL_LAST				148
> +#define OPAL_OCC_COMMAND			149
> +#define OPAL_LAST				149
>  
>  /* Device tree flags */
>  
> @@ -829,6 +834,40 @@ struct opal_prd_msg_header {
>  
>  struct opal_prd_msg;
>  
> +enum occ_cmd {
> +	OCC_CMD_AMESTER_PASS_THRU = 0,
> +	OCC_CMD_CLEAR_SENSOR_DATA,
> +	OCC_CMD_SET_POWER_CAP,
> +	OCC_CMD_SET_POWER_SHIFTING_RATIO,
> +	OCC_CMD_SELECT_SENSOR_GROUPS,
> +	OCC_CMD_LAST
> +};
> +
> +struct opal_occ_cmd_rsp_msg {
> +	__be64 cdata;
> +	__be64 rdata;
> +	__be16 cdata_size;
> +	__be16 rdata_size;
> +	u8 cmd;
> +	u8 request_id;
> +	u8 status;
> +};
> +
> +struct opal_occ_cmd_data {
> +	__be16 size;
> +	u8 cmd;
> +	u8 data[];
> +};
> +
> +struct opal_occ_rsp_data {
> +	__be16 size;
> +	u8 status;
> +	u8 data[];
> +};
> +
> +#define MAX_OPAL_CMD_DATA_LENGTH        4090
> +#define MAX_OCC_RSP_DATA_LENGTH         8698
> +
>  #define OCC_RESET                       0
>  #define OCC_LOAD                        1
>  #define OCC_THROTTLE                    2
> diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
> index 03ed493..e55ed79 100644
> --- a/arch/powerpc/include/asm/opal.h
> +++ b/arch/powerpc/include/asm/opal.h
> @@ -346,6 +346,9 @@ static inline int opal_get_async_rc(struct opal_msg msg)
>  
>  void opal_wake_poller(void);
>  
> +int64_t opal_occ_command(int chip_id, struct opal_occ_cmd_rsp_msg *msg,
> +			 bool retry);
> +
>  #endif /* __ASSEMBLY__ */
>  
>  #endif /* _ASM_POWERPC_OPAL_H */
> diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
> index b5d98cb..f5f0902 100644
> --- a/arch/powerpc/platforms/powernv/Makefile
> +++ b/arch/powerpc/platforms/powernv/Makefile
> @@ -2,7 +2,7 @@ obj-y			+= setup.o opal-wrappers.o opal.o opal-async.o idle.o
>  obj-y			+= opal-rtc.o opal-nvram.o opal-lpc.o opal-flash.o
>  obj-y			+= rng.o opal-elog.o opal-dump.o opal-sysparam.o opal-sensor.o
>  obj-y			+= opal-msglog.o opal-hmi.o opal-power.o opal-irqchip.o
> -obj-y			+= opal-kmsg.o
> +obj-y			+= opal-kmsg.o opal-occ.o
>  
>  obj-$(CONFIG_SMP)	+= smp.o subcore.o subcore-asm.o
>  obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o
> diff --git a/arch/powerpc/platforms/powernv/opal-occ.c b/arch/powerpc/platforms/powernv/opal-occ.c
> new file mode 100644
> index 0000000..912cdc4
> --- /dev/null
> +++ b/arch/powerpc/platforms/powernv/opal-occ.c
> @@ -0,0 +1,314 @@
> +/*
> + * Copyright IBM Corporation 2017
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#define pr_fmt(fmt) "opal-occ: " fmt
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/miscdevice.h>
> +#include <linux/highmem.h>
> +#include <linux/slab.h>
> +#include <asm/opal.h>
> +
> +struct occ {
> +	struct miscdevice dev;
> +	struct opal_occ_rsp_data *rsp;
> +	atomic_t session;
> +	atomic_t cmd_in_progress;
> +	int id;
> +	u8 last_token;
> +} *occs;
> +static int nr_occs;
> +
> +static int __send_occ_command(struct opal_occ_cmd_rsp_msg *msg,
> +			      int chip_id, bool retry)
> +{
> +	struct opal_msg async_msg;
> +	int rc;
> +
> +	if (!retry) {
> +		msg->cdata = cpu_to_be64(__pa(msg->cdata));
> +		msg->cdata_size = cpu_to_be16(msg->cdata_size);
> +		msg->rdata = cpu_to_be64(__pa(msg->rdata));
> +	}
> +
> +	rc = opal_occ_command(chip_id, msg, retry);
> +	if (rc == OPAL_ASYNC_COMPLETION) {
> +		rc = opal_async_wait_response(msg->request_id, &async_msg);
> +		if (rc) {
> +			pr_info("Failed to wait for async response %d\n", rc);
> +			return rc;
> +		}
> +	} else if (rc) {
> +		pr_info("Failed to send opal_occ_command %d\n", rc);
> +		return rc;
> +	}
> +
> +	rc = opal_get_async_rc(async_msg);
> +	if (rc) {
> +		pr_info("opal_occ_command failed with %d\n", rc);
> +		return rc;
> +	}

If you get a timeout or a response mismatch you're going to retry. Is
this because you expect this to happen generally in the course of using
this interface - if so, should you print a message or would it be best
to say nothing? Also is pr_info() a good level for these?

> +
> +	msg->rdata_size = be16_to_cpu(msg->rdata_size);
> +	msg->rdata = be64_to_cpu(__va(msg->rdata));
> +	msg->cdata_size = be16_to_cpu(msg->cdata_size);
> +	msg->cdata = be64_to_cpu(__va(msg->cdata));
> +
> +	if (msg->rdata_size > MAX_OCC_RSP_DATA_LENGTH) {
> +		pr_info("Opal sent bigger data, clipping to the max response size\n");
> +		msg->rdata_size = MAX_OCC_RSP_DATA_LENGTH;
> +	}
> +
> +	return rc;
> +}
> +
> +static int send_occ_command(struct opal_occ_cmd_rsp_msg *msg, struct occ *occ)
> +{
> +	int token, rc;
> +
> +	token = opal_async_get_unique_token_interruptible(occ->last_token);
> +	if (token < 0) {
> +		pr_info("Failed to get the request_id/token for command %d (%d)\n",
> +			msg->cmd, token);
> +		return token;
> +	}
> +
> +	msg->request_id = token;
> +	rc = __send_occ_command(msg, occ->id, false);
> +
> +	switch (rc) {
> +	case OPAL_OCC_CMD_TIMEOUT:
> +	case OPAL_OCC_RSP_MISMATCH:
> +		occ->last_token = token;
> +		opal_async_release_token(token);
> +		token = opal_async_get_unique_token_interruptible(token);
> +		if (token < 0) {
> +			pr_info("Failed to get the request_id/token for retry command %d (%d)\n",
> +				msg->cmd, token);
> +
> +			return opal_error_code(rc);
> +		}
> +
> +		msg->request_id = token;
> +		rc = __send_occ_command(msg, occ->id, true);
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	occ->last_token = token;
> +	opal_async_release_token(token);
> +	return opal_error_code(rc);
> +}
> +
> +static int opal_occ_cmd_prepare(struct opal_occ_cmd_data *cmd, struct occ *occ)
> +{
> +	struct opal_occ_cmd_rsp_msg msg;
> +	int rc;
> +
> +	msg.cmd = cmd->cmd;
> +	msg.cdata_size = cmd->size;
> +	msg.rdata = (u64)occ->rsp->data;
> +	msg.cdata = (u64)cmd->data;

I'm surprised this doesn't throw (gcc) warnings, I certainly expect it
will throw sparse warnings.

You've done the right thing and annotated your struct
opal_occ_cmd_rsp_msg with __be64 which is what skiboot expects,
however, at this point it is still in CPU endian and it can get
confusing. If a type is marked as a specific endian, it should *always*
be in that endian. In this case it may (depending on what the CPU
endian is) be in the wrong endian until we get to __send_occ_command()
where you do the conversion. Is there any reason you can't convert them
here?

> +	rc = send_occ_command(&msg, occ);
> +	if (rc)
> +		return rc;
> +
> +	occ->rsp->size = msg.rdata_size;
> +	occ->rsp->status = msg.status;
> +
> +	return rc;
> +}
> +
> +static ssize_t opal_occ_write(struct file *file, const char __user *buf,
> +			      size_t count, loff_t *ppos)
> +{
> +	struct miscdevice *dev = file->private_data;
> +	struct occ *occ = container_of(dev, struct occ, dev);
> +	struct opal_occ_cmd_data *cmd;
> +	int rc;
> +
> +	if (count < sizeof(*cmd))
> +		return -EINVAL;
> +
> +	if (atomic_xchg(&occ->cmd_in_progress, 1) == 1)
> +		return -EBUSY;
> +
> +	cmd = kmalloc(count, GFP_KERNEL);
> +	if (!cmd) {
> +		rc = -ENOMEM;
> +		goto out;
> +	}
> +
> +	rc = copy_from_user(cmd, buf, count);
> +	if (rc) {
> +		pr_err("Failed to copy OCC command request message\n");
> +		rc = -EFAULT;
> +		goto free_cmd;
> +	}
> +
> +	if (cmd->size > MAX_OPAL_CMD_DATA_LENGTH) {
> +		rc = -EINVAL;
> +		goto free_cmd;
> +	}
> +
> +	rc = opal_occ_cmd_prepare(cmd, occ);
> +	if (!rc)
> +		rc = count;
> +
> +free_cmd:
> +	kfree(cmd);
> +out:
> +	atomic_xchg(&occ->cmd_in_progress, 0);
> +	return rc;
> +}
> +
> +static ssize_t opal_occ_read(struct file *file, char __user *buf,
> +			     size_t count, loff_t *ppos)
> +{
> +	struct miscdevice *dev = file->private_data;
> +	struct occ *occ = container_of(dev, struct occ, dev);
> +	int rc;
> +
> +	if (count < sizeof(*occ->rsp) + occ->rsp->size)
> +		return -EINVAL;
> +
> +	rc = copy_to_user((void __user *)buf, occ->rsp,
> +			  sizeof(occ->rsp) + occ->rsp->size);
> +	if (rc) {
> +		pr_err("Failed to copy OCC response data to user\n");
> +		return rc;
> +	}
> +
> +	return sizeof(*occ->rsp) + occ->rsp->size;
> +}
> +
> +static int opal_occ_open(struct inode *inode, struct file *file)
> +{
> +	struct miscdevice *dev = file->private_data;
> +	struct occ *occ = container_of(dev, struct occ, dev);
> +
> +	if (atomic_xchg(&occ->session, 1) == 1)
> +		return -EBUSY;
> +
> +	return 0;
> +}
> +
> +static int opal_occ_release(struct inode *inode, struct file *file)
> +{
> +	struct miscdevice *dev = file->private_data;
> +	struct occ *occ = container_of(dev, struct occ, dev);
> +
> +	atomic_xchg(&occ->session, 0);
> +
> +	return 0;
> +}
> +
> +static const struct file_operations opal_occ_fops = {
> +	.open		= opal_occ_open,
> +	.read		= opal_occ_read,
> +	.write		= opal_occ_write,
> +	.release	= opal_occ_release,
> +	.owner		= THIS_MODULE,
> +};
> +
> +static int opal_occ_probe(struct platform_device *pdev)
> +{
> +	unsigned int chip[256];
> +	unsigned int cpu;
> +	unsigned int prev_chip_id = UINT_MAX;
> +	int i, rc;
> +
> +	for_each_possible_cpu(cpu) {
> +		unsigned int id = cpu_to_chip_id(cpu);
> +
> +		if (prev_chip_id != id) {
> +			prev_chip_id = id;
> +			chip[nr_occs++] = id;
> +			WARN_ON(nr_occs > 254);

Perhaps have some MAX_POSSIBLE_CHIPS or something? Also might I suggest
WARN_ON_ONCE just because if there's no point printing the warning more
than once but this code could print it a bunch of times...

> +		}
> +	}
> +
> +	occs = kcalloc(nr_occs, sizeof(*occs), GFP_KERNEL);
> +	if (!occs)
> +		return -ENOMEM;
> +
> +	for (i = 0; i < nr_occs; i++) {
> +		char name[10];
> +
> +		occs[i].id = chip[i];
> +		occs[i].dev.minor = MISC_DYNAMIC_MINOR;
> +		snprintf(name, 10, "occ%d", chip[i]);
> +		occs[i].dev.name = name;
> +		occs[i].dev.fops = &opal_occ_fops;
> +		occs[i].last_token = -1;
> +		occs[i].rsp = kmalloc(sizeof(occs[i].rsp) +
> +				      MAX_OCC_RSP_DATA_LENGTH,
> +				      GFP_KERNEL);
> +		if (!occs[i].rsp) {
> +			rc = -ENOMEM;
> +			goto free_occs;
> +		}
> +
> +		rc = misc_register(&occs[i].dev);
> +		if (rc)
> +			goto free_occ_rsp_data;
> +	}
> +
> +	return 0;
> +
> +free_occ_rsp_data:
> +	kfree(occs[i].rsp);
> +free_occs:
> +	while (--i >= 0) {
> +		kfree(occs[i].rsp);
> +		misc_deregister(&occs[i].dev);
> +	}
> +	kfree(occs);
> +
> +	return rc;
> +}
> +
> +static int opal_occ_remove(struct platform_device *pdev)
> +{
> +	int i;
> +
> +	for (i = 0; i < nr_occs; i++) {
> +		kfree(occs[i].rsp);
> +		misc_deregister(&occs[i].dev);
> +	}
> +
> +	kfree(occs);
> +	return 0;
> +}
> +
> +static const struct of_device_id opal_occ_match[] = {
> +	{ .compatible = "ibm,opal-occ-cmd-rsp-interface" },
> +	{ },
> +};
> +
> +static struct platform_driver opal_occ_driver = {
> +	.driver = {
> +		.name           = "opal-occ",
> +		.of_match_table = opal_occ_match,
> +	},
> +	.probe	= opal_occ_probe,
> +	.remove	= opal_occ_remove,
> +};
> +
> +module_platform_driver(opal_occ_driver);
> +
> +MODULE_DESCRIPTION("PowerNV OPAL-OCC driver");
> +MODULE_LICENSE("GPL");
> diff --git a/arch/powerpc/platforms/powernv/opal-wrappers.S b/arch/powerpc/platforms/powernv/opal-wrappers.S
> index f620572..e6bf18d 100644
> --- a/arch/powerpc/platforms/powernv/opal-wrappers.S
> +++ b/arch/powerpc/platforms/powernv/opal-wrappers.S
> @@ -310,3 +310,4 @@ OPAL_CALL(opal_xive_dump,			OPAL_XIVE_DUMP);
>  OPAL_CALL(opal_npu_init_context,		OPAL_NPU_INIT_CONTEXT);
>  OPAL_CALL(opal_npu_destroy_context,		OPAL_NPU_DESTROY_CONTEXT);
>  OPAL_CALL(opal_npu_map_lpar,			OPAL_NPU_MAP_LPAR);
> +OPAL_CALL(opal_occ_command,			OPAL_OCC_COMMAND);
> diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
> index 59684b4..d87c61b 100644
> --- a/arch/powerpc/platforms/powernv/opal.c
> +++ b/arch/powerpc/platforms/powernv/opal.c
> @@ -815,6 +815,9 @@ static int __init opal_init(void)
>  	opal_pdev_init("ibm,opal-flash");
>  	opal_pdev_init("ibm,opal-prd");
>  
> +	/* Initialize platform device: OCC_OPAL command-response interface */
> +	opal_pdev_init("ibm,opal-occ-cmd-rsp-interface");
> +
>  	/* Initialise platform device: oppanel interface */
>  	opal_pdev_init("ibm,opal-oppanel");
>  
> @@ -859,6 +862,7 @@ void opal_shutdown(void)
>  EXPORT_SYMBOL_GPL(opal_flash_write);
>  EXPORT_SYMBOL_GPL(opal_flash_erase);
>  EXPORT_SYMBOL_GPL(opal_prd_msg);
> +EXPORT_SYMBOL_GPL(opal_occ_command);
>  
>  /* Convert a region of vmalloc memory to an opal sg list */
>  struct opal_sg_list *opal_vmalloc_to_sg_list(void *vmalloc_addr,
> @@ -937,6 +941,10 @@ int opal_error_code(int rc)
>  	case OPAL_UNSUPPORTED:		return -EIO;
>  	case OPAL_HARDWARE:		return -EIO;
>  	case OPAL_INTERNAL_ERROR:	return -EIO;
> +	case OPAL_OCC_BUSY:		return -EBUSY;
> +	case OPAL_OCC_INVALID_STATE:
> +	case OPAL_OCC_CMD_TIMEOUT:
> +	case OPAL_OCC_RSP_MISMATCH:	return -EIO;
>  	default:
>  		pr_err("%s: unexpected OPAL error %d\n", __func__, rc);
>  		return -EIO;