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

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Message-ID: <236606947b691049c650bdf82c37324084662147.camel@HansenPartnership.com>
Date: Tue, 21 May 2024 09:26:28 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, linux-integrity@...r.kernel.org
Cc: keyrings@...r.kernel.org, Peter Huewe <peterhuewe@....de>, Jason
 Gunthorpe <jgg@...pe.ca>, Mimi Zohar <zohar@...ux.ibm.com>, David Howells
 <dhowells@...hat.com>, Paul Moore <paul@...l-moore.com>, James Morris
 <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
 linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH] tpm: enable HMAC encryption for only x86-64 and aarch64

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@...senPartnership.com>
> Fixes: d2add27cf2b8 ("tpm: Add NULL primary creation")
> Closes:
> https://lore.kernel.org/linux-integrity/D1FCAPJSYLTS.R9VC1CXDCIHH@kernel.org/
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> ---
>  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@...senPartnership.com>

James