Re: [PATCH v5 10/15] cxl: Add support for fwctl RPC command to enable CXL feature commands

[Dan Williams <dan.j.williams@intel.com>]

Saeed Mahameed wrote:
> On 11 Feb 11:28, Dave Jiang wrote:
> >fwctl provides a fwctl_ops->fw_rpc() callback in order to issue ioctls
> >to a device. The cxl fwctl driver will start by supporting the CXL
> >Feature commands: Get Supported Features, Get Feature, and Set Feature.
> >
> >The fw_rpc() callback provides 'enum fwctl_rpc_scope' parameter where
> >it indicates the security scope of the call. The Get Supported Features
> >and Get Feature calls can be executed with the scope of
> >FWCTL_RPC_CONFIGRATION. The Set Feature call is gated by the effects
> >of the Feature reported by Get Supported Features call for the specific
> >Feature.
> >
> >Only "Get Supported Features" is supported in this patch. Additional
> >commands will be added in follow on patches. "Get Supported Features"
> >will filter the Features that are exclusive to the kernel. The flag
> >field of the Feature details will be cleared of the "Changeable"
> >field and the "set feat size" will be set to 0 to indicate that
> >the feature is not changeable.
> >
> >Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> >Reviewed-by: Dan Williams <dan.j.williams@intel.com>
[..]
> >+	/*
> >+	 * If the Feature setting causes immediate configuration change
> >+	 * then we need the full write permission policy.
> >+	 */
> >+	if (effects & imm_mask && scope >= FWCTL_RPC_DEBUG_WRITE_FULL)
> >+		return true;
> 
> I am not sure the security policy here is coherent with the documentation
>   * @FWCTL_RPC_DEBUG_WRITE_FULL: Write access to all debug information
> 
>  From the documentation these features settings in CXL should only be for
> debug purposes, a bit confusing, same for below.

Have another read through the FWCTL documentation. The reason the term
"debug write" is used is due to the expectation that FWCTL manipulates
ancillary functionality of the device. It is "debug" because FWCTL
Feature support can be disabled without losing access to the primary
capabilties of the device.

For the same way debugfs enables some non-debug flows, but is
disabled in kernel lockdown scenarios, FWCTL enables some non-debug
flows and is disabled in kernel lockdown scenarios.