Date:   Fri, 20 May 2022 17:37:32 -0700
From:   Russ Weight <russell.h.weight@...el.com>
To:     Xu Yilun <yilun.xu@...el.com>
CC:     <mdf@...nel.org>, <hao.wu@...el.com>, <lee.jones@...aro.org>,
        <linux-fpga@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <trix@...hat.com>, <marpagan@...hat.com>, <lgoncalv@...hat.com>,
        <matthew.gerlach@...ux.intel.com>,
        <basheer.ahmed.muddebihal@...el.com>, <tianfei.zhang@...el.com>
Subject: Re: [PATCH v20 3/5] fpga: m10bmc-sec: expose max10 flash update count



On 5/18/22 00:10, Xu Yilun wrote:
> On Tue, May 17, 2022 at 09:16:50AM -0700, Russ Weight wrote:
>>
>> On 5/16/22 21:13, Xu Yilun wrote:
>>> On Mon, May 16, 2022 at 04:49:39PM -0700, Russ Weight wrote:
>>>> Extend the MAX10 BMC Secure Update driver to provide a sysfs file to
>>>> expose the flash update count.
>>>>
>>>> Signed-off-by: Russ Weight <russell.h.weight@...el.com>
>>>> Reviewed-by: Tom Rix <trix@...hat.com>
>>>> ---
>>>> v20:
>>>>   - No change
>>>> v19:
>>>>   - Change "card bmc" naming back to "m10 bmc" naming to be consistent
>>>>     with the parent driver.
>>>> v18:
>>>>   - No change
>>>> v17:
>>>>   - Update the Date and KernelVersion for the ABI documentation to Jul 2022
>>>>     and 5.19 respectively.
>>>>   - Change "m10bmc" in symbol names to "cardbmc" to reflect the fact that the
>>>>     future devices will not necessarily use the MAX10.
>>>> v16:
>>>>   - No Change
>>>> v15:
>>>>   - Updated the Dates and KernelVersions in the ABI documentation
>>>> v14:
>>>>   - No change
>>>> v13:
>>>>   - Updated ABI documentation date and kernel version
>>>> v12:
>>>>   - Updated Date and KernelVersion fields in ABI documentation
>>>> v11:
>>>>   - No change
>>>> v10:
>>>>   - Changed the path expression in the sysfs documentation to
>>>>     replace the n3000 reference with something more generic to
>>>>     accomodate other devices that use the same driver.
>>>> v9:
>>>>   - Rebased to 5.12-rc2 next
>>>>   - Updated Date and KernelVersion in ABI documentation
>>>> v8:
>>>>   - Previously patch 3/6, otherwise no change
>>>> v7:
>>>>   - Updated Date and KernelVersion in ABI documentation
>>>> v6:
>>>>   - Changed flash_count_show() parameter list to achieve
>>>>     reverse-christmas tree format.
>>>>   - Added WARN_ON() call for (FLASH_COUNT_SIZE / stride) to ensure
>>>>     that the proper count is passed to regmap_bulk_read().
>>>> v5:
>>>>   - Renamed sysfs node user_flash_count to flash_count and updated the
>>>>     sysfs documentation accordingly.
>>>> v4:
>>>>   - Moved the sysfs file for displaying the flash count from the
>>>>     FPGA Security Manager class driver to here. The
>>>>     m10bmc_user_flash_count() function is removed and the
>>>>     functionality is moved into a user_flash_count_show()
>>>>     function.
>>>>   - Added ABI documentation for the new sysfs entry
>>>> v3:
>>>>   - Changed: iops -> sops, imgr -> smgr, IFPGA_ -> FPGA_, ifpga_ to fpga_
>>>>   - Changed "MAX10 BMC Secure Engine driver" to "MAX10 BMC Secure Update
>>>>     driver"
>>>>   - Removed wrapper functions (m10bmc_raw_*, m10bmc_sys_*). The
>>>>     underlying functions are now called directly.
>>>> v2:
>>>>   - Renamed get_qspi_flash_count() to m10bmc_user_flash_count()
>>>>   - Minor code cleanup per review comments
>>>>   - Added m10bmc_ prefix to functions in m10bmc_iops structure
>>>> ---
>>>>  .../sysfs-driver-intel-m10-bmc-sec-update     |  8 +++++
>>>>  drivers/fpga/intel-m10-bmc-sec-update.c       | 36 +++++++++++++++++++
>>>>  2 files changed, 44 insertions(+)
>>>>
>>>> diff --git a/Documentation/ABI/testing/sysfs-driver-intel-m10-bmc-sec-update b/Documentation/ABI/testing/sysfs-driver-intel-m10-bmc-sec-update
>>>> index 2bb271695e14..1132e39b2125 100644
>>>> --- a/Documentation/ABI/testing/sysfs-driver-intel-m10-bmc-sec-update
>>>> +++ b/Documentation/ABI/testing/sysfs-driver-intel-m10-bmc-sec-update
>>>> @@ -27,3 +27,11 @@ Description:	Read only. Returns the root entry hash for the BMC image
>>>>  		"hash not programmed".  This file is only visible if the
>>>>  		underlying device supports it.
>>>>  		Format: string.
>>>> +
>>>> +What:		/sys/bus/platform/drivers/intel-m10bmc-sec-update/.../security/flash_count
>>>> +Date:		Jul 2022
>>>> +KernelVersion:	5.19
>>>> +Contact:	Russ Weight <russell.h.weight@...el.com>
>>>> +Description:	Read only. Returns number of times the secure update
>>>> +		staging area has been flashed.
>>>> +		Format: "%u".
>>>> diff --git a/drivers/fpga/intel-m10-bmc-sec-update.c b/drivers/fpga/intel-m10-bmc-sec-update.c
>>>> index f9f39d2cfe5b..3f183202de3b 100644
>>>> --- a/drivers/fpga/intel-m10-bmc-sec-update.c
>>>> +++ b/drivers/fpga/intel-m10-bmc-sec-update.c
>>>> @@ -78,7 +78,43 @@ DEVICE_ATTR_SEC_REH_RO(bmc, BMC_PROG_MAGIC, BMC_PROG_ADDR, BMC_REH_ADDR);
>>>>  DEVICE_ATTR_SEC_REH_RO(sr, SR_PROG_MAGIC, SR_PROG_ADDR, SR_REH_ADDR);
>>>>  DEVICE_ATTR_SEC_REH_RO(pr, PR_PROG_MAGIC, PR_PROG_ADDR, PR_REH_ADDR);
>>>>  
>>>> +#define FLASH_COUNT_SIZE 4096	/* count stored as inverted bit vector */
>>>> +
>>>> +static ssize_t flash_count_show(struct device *dev,
>>>> +				struct device_attribute *attr, char *buf)
>>>> +{
>>>> +	struct m10bmc_sec *sec = dev_get_drvdata(dev);
>>>> +	unsigned int stride, num_bits;
>>>> +	u8 *flash_buf;
>>>> +	int cnt, ret;
>>>> +
>>>> +	stride = regmap_get_reg_stride(sec->m10bmc->regmap);
>>>> +	num_bits = FLASH_COUNT_SIZE * 8;
>>>> +
>>>> +	flash_buf = kmalloc(FLASH_COUNT_SIZE, GFP_KERNEL);
>>>> +	if (!flash_buf)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	WARN_ON(FLASH_COUNT_SIZE % stride);
>>> The same concern here. Stop users from getting the broken value.
>> Sure - I will change this.
>>
>> I was using WARN_ON() because it indicates a problem in the device or
>> the driver itself. It is not really validating information from userspace.
> Understood. So it is OK we keep the WARN_ON, or WARN_ON_ONCE？But we
> should still have some code to handle the issue gracefully rather
> than just passing the broken value to user.
Yes, I have gone through each of these cases and made sure that they
return an error rather than garbage. I have also added kernel logging
in some cases.

Thanks,
- Russ
>
> Thanks
> Yilun
>
>> As I understand it, WARN_ON() is used to log such events to the kernel
>> log. If this isn't an appropriate use of WARN_ON(), then when should I
>> consider using it?
>>
>> Thanks,
>> - Russ
>>>> +	ret = regmap_bulk_read(sec->m10bmc->regmap, STAGING_FLASH_COUNT,
>>>> +			       flash_buf, FLASH_COUNT_SIZE / stride);
>>>> +	if (ret) {
>>>> +		dev_err(sec->dev,
>>>> +			"failed to read flash count: %x cnt %x: %d\n",
>>>> +			STAGING_FLASH_COUNT, FLASH_COUNT_SIZE / stride, ret);
>>>> +		goto exit_free;
>>>> +	}
>>>> +	cnt = num_bits - bitmap_weight((unsigned long *)flash_buf, num_bits);
>>>> +
>>>> +exit_free:
>>>> +	kfree(flash_buf);
>>>> +
>>>> +	return ret ? : sysfs_emit(buf, "%u\n", cnt);
>>>> +}
>>>> +static DEVICE_ATTR_RO(flash_count);
>>>> +
>>>>  static struct attribute *m10bmc_security_attrs[] = {
>>>> +	&dev_attr_flash_count.attr,
>>>>  	&dev_attr_bmc_root_entry_hash.attr,
>>>>  	&dev_attr_sr_root_entry_hash.attr,
>>>>  	&dev_attr_pr_root_entry_hash.attr,
>>>> -- 
>>>> 2.25.1

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