Re: [PATCH 2/4] efi/libstub: Add Confidential Computing (CC) measurement typedefs

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 3/5/24 10:00 AM, Ilias Apalodimas wrote:
> Hi Ard,
>
> On Mon, 4 Mar 2024 at 12:44, Ard Biesheuvel <ardb+git@google.com> wrote:
>> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>>
>> If the virtual firmware implements TPM support, TCG2 protocol will be
>> used for kernel measurements and event logging support. But in CC
>> environment, not all platforms support or enable the TPM feature. UEFI
>> specification [1] exposes protocol and interfaces used for kernel
>> measurements in CC platforms without TPM support.
>>
>> More details about the EFI CC measurements and logging can be found
>> in [1].
>>
>> Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#efi-cc-measurement-protocol [1]
>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>> [ardb: Drop code changes, keep typedefs and #define's only]
>> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>> ---
>>  drivers/firmware/efi/libstub/efistub.h | 79 ++++++++++++++++++++
>>  include/linux/efi.h                    |  1 +
>>  2 files changed, 80 insertions(+)
>>
> [...]
>
>> +
>> +struct efi_cc_event {
>> +       u32 event_size;
>> +       struct {
>> +               u32 header_size;
>> +               u16 header_version;
>> +               u32 mr_index;
>> +               u32 event_type;
>> +       } __packed event_header;
>> +       u8 event_data[0];
> We should define this as a flexible array member instead of a zero-length array?
> The spec is funny and defines this as event_data[1]. I think we aren't
> using the sizeof(struct efi_cc_event) anywhere, so if this struct is
> not used as a member of another struct or an array we can omit it
> entirely.

Flexible array is also fine or we can just add a comment like "u8[] event follows here"
like in struct efi_tcg2_event .

>
> [...]
>
> Cheers
> /Ilias

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer