tpm: Disable TPM2_TCG_HMAC by default

After reading all the feedback, right now disabling the TPM2_TCG_HMAC
is the right call.

Other views discussed:

A. Having a kernel command-line parameter or refining the feature
   otherwise. This goes to the area of improvements.  E.g., one
   example is my own idea where the null key specific code would be
   replaced with a persistent handle parameter (which can be
   *unambigously* defined as part of attestation process when
   done correctly).

B. Removing the code. I don't buy this because that is same as saying
   that HMAC encryption cannot work at all (if really nitpicking) in
   any form. Also I disagree on the view that the feature could not
   be refined to something more reasoable.

Also, both A and B are worst options in terms of backporting.

Thuss, this is the best possible choice.

Cc: stable@vger.kernel.or # v6.10+
Fixes: d2add27cf2b8 ("tpm: Add NULL primary creation")
Suggested-by: Chris Fenner <cfenn@google.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index ba3924eb13ba8926df50e3007a27317da24078dd..99c6fde288105fcc1ea3f30b0387e86e51355fa2 100644 (file)
--- 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 X86_64
+       default n
        select CRYPTO_ECDH
        select CRYPTO_LIB_AESCFB
        select CRYPTO_LIB_SHA256