Re: [PATCH v3 2/5] tsm-mr: Add tsm-mr sample code

[Dan Williams]

Cedric Xing wrote:
> This sample kernel module demonstrates how to make MRs accessible to user
> mode through the tsm-mr library.
> 
> Once loaded, this module registers a `miscdevice` that host a set of
> emulated measurement registers as shown in the directory tree below.
> 
> /sys/class/misc/tsm_mr_sample
> └── emulated_mr
>     ├── config_mr
>     ├── report_digest:sha512
>     ├── rtmr0:sha256
>     ├── rtmr1:sha384
>     ├── rtmr_crypto_agile:sha256
>     ├── rtmr_crypto_agile:sha384
>     └── static_mr:sha384
> 
> Among the MRs in this example:
> 
> - `config_mr` demonstrates a hashless MR, like MRCONFIGID in Intel TDX or
>   HOSTDATA in AMD SEV.
> - `static_mr` demonstrates a static MR. The suffix `:sha384` indicates its
>   value is a sha384 digest.
> - `rtmr0` is an RTMR with `TSM_MR_F_WRITABLE` **cleared**, preventing
>   direct extensions; as a result, the attribute `rtmr0:sha256` is
>   read-only.
> - `rtmr1` is an RTMR with `TSM_MR_F_WRITABLE` **set**, permitting direct
>   extensions; thus, the attribute `rtmr1:sha384` is writable.
> - `rtmr_crypto_agile` demonstrates a "single" MR that supports multiple
>   hash algorithms. Each supported algorithm has a corresponding digest,
>   usually referred to as a "bank" in TCG terminology. In this specific
>   sample, the 2 banks are aliased to `rtmr0` and `rtmr1`, respectively.
> - `report_digest` contains the digest of the internal report structure
>   living in this sample module's memory. It is to demonstrate the use of
>   the `TSM_MR_F_LIVE` flag. Its value changes each time an RTMR is
>   extended.
> 
> Signed-off-by: Cedric Xing <cedric.xing@xxxxxxxxx>
[..]
> +static struct tsm_measurements emulated_mr = {
> +	.name = "emulated_mr",

I think the convention should be that all consumers use a common name
for this common ABI, similar to a sysfs-class. So, I would say set the
name to "measurement_registers" inside tsm_mr_create_attribute_group(),
and make the "custom name" or "no-name" case an isolated corner case.

Other than that, thanks for taking the time to build this sample it
makes the reviewing the implementation easier and allows for some ABI
testing.