Re: [PATCH] tpm: enable HMAC encryption for only x86-64 and aarch64

[James Bottomley]

On Tue, 2024-05-21 at 16:09 +0300, Jarkko Sakkinen wrote:
> Let's be more conservative and enable HMAC by default only for the
> platforms where it immediately makes sense, i.e. x86-64 and aarch64.
> This can be relaxed later on, and obviously the kconfig option can be
> set even if not default on a particular arch.
> 
> Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
> Fixes: d2add27cf2b8 ("tpm: Add NULL primary creation")
> Closes:
> https://lore.kernel.org/linux-integrity/D1FCAPJSYLTS.R9VC1CXDCIHH@xxxxxxxxxx/
> Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
> ---
>  drivers/char/tpm/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> index e63a6a17793c..19e61dcfcbbe 100644
> --- a/drivers/char/tpm/Kconfig
> +++ b/drivers/char/tpm/Kconfig
> @@ -29,7 +29,7 @@ if TCG_TPM
>  
>  config TCG_TPM2_HMAC
>         bool "Use HMAC and encrypted transactions on the TPM bus"
> -       default y
> +       default X86_64 || ARM64

My first instinct is to say that devices in hostile environments (like
IoT) are likely in the most need of this.  However, it is an
experimental feature, so I would like to debug it first in the
environments where it's expected to work, which is desktop and laptop,
so I'm happy with this:

Acked-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>

James