Re: [PATCH v20 3/5] fpga: m10bmc-sec: expose max10 flash update count

[Xu Yilun <yilun.xu@intel.com>]

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@intel.com>
> >> Reviewed-by: Tom Rix <trix@redhat.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@intel.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.

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