[PATCH v2 2/9] tpm: Avoid code bloat when not using EFI_TCG2_PROTOCOL

[Ilias Apalodimas]

Hi Simon,

On Mon, 10 Jun 2024 at 17:59, Simon Glass <sjg at chromium.org> wrote:
>
> It does not make sense to enable all SHA algorithms unless they are
> needed. It bloats the code and in this case, causes chromebook_link to
> fail to build. That board does use the TPM, but not with measured boot,
> nor EFI.
>
> Since EFI_TCG2_PROTOCOL already selects these options, we just need to
> add them to MEASURED_BOOT as well.
>
> Note that the original commit combines refactoring and new features,
> which makes it hard to see what is going on.
>
> Fixes: 97707f12fda tpm: Support boot measurements
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
> Changes in v2:
> - Put the conditions under EFI_TCG2_PROTOCOL
> - Consider MEASURED_BOOT too
>
>  boot/Kconfig | 4 ++++
>  lib/Kconfig  | 4 ----
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/boot/Kconfig b/boot/Kconfig
> index 6f3096c15a6..b061891e109 100644
> --- a/boot/Kconfig
> +++ b/boot/Kconfig
> @@ -734,6 +734,10 @@ config LEGACY_IMAGE_FORMAT
>  config MEASURED_BOOT
>         bool "Measure boot images and configuration when booting without EFI"
>         depends on HASH && TPM_V2
> +       select SHA1
> +       select SHA256
> +       select SHA384
> +       select SHA512
>         help
>           This option enables measurement of the boot process when booting
>           without UEFI . Measurement involves creating cryptographic hashes
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 189e6eb31aa..568892fce44 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -438,10 +438,6 @@ config TPM
>         bool "Trusted Platform Module (TPM) Support"
>         depends on DM
>         imply DM_RNG
> -       select SHA1
> -       select SHA256
> -       select SHA384
> -       select SHA512

I am not sure this is the right way to deal with your problem.
The TPM main functionality is to measure and extend PCRs, so shaXXXX
is really required. To make things even worse, you don't know the PCR
banks that are enabled beforehand. This is a runtime config of the
TPM.

 So this would make the TPM pretty useless. Can't you remove something
that doesn't break functionality?

Thanks
/Ilias
>         help
>           This enables support for TPMs which can be used to provide security
>           features for your board. The TPM can be connected via LPC or I2C
> --
> 2.34.1
>