linux-kernel - Re: [PATCH 1/3] tpm: Disable TCG_TPM2

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Date: Tue, 21 May 2024 08:03:24 +0100
From: Vitor Soares <ivitro@...il.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, linux-integrity@...r.kernel.org
Cc: keyrings@...r.kernel.org, James.Bottomley@...senPartnership.com, 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 1/3] tpm: Disable TCG_TPM2_HMAC by default

Hi Jarkko,

On Mon, 2024-05-20 at 02:51 +0300, Jarkko Sakkinen wrote:
> Causes performance drop in initialization so needs to be opt-in.
> Distributors are capable of opt-in enabling this. Could be also handled by
> kernel-command line in the future.
> 
> Reported-by: Vitor Soares <ivitro@...il.com>
> Closes:
> https://lore.kernel.org/linux-integrity/bf67346ef623ff3c452c4f968b7d900911e250c3.camel@gmail.com/#t
> Fixes: d2add27cf2b8 ("tpm: Add NULL primary creation")
> 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..db41301e63f2 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 n
>         select CRYPTO_ECDH
>         select CRYPTO_LIB_AESCFB
>         select CRYPTO_LIB_SHA256

I did the test on my side, and with TCG_TPM2_HMAC set to "n" the time to probe
tpm_tis_spi driver has reduced to:
real    0m2.009s
user    0m0.001s
sys     0m0.019s

Thanks for your help.

Best regards,
Vitor Soares