Re: [PATCH v4 1/5] KEYS: trusted: allow use of TEE as backend without TCG_TPM support

Jarkko Sakkinen
2021-12-05T00:13:38Z

On Mon, Oct 11, 2021 at 12:02:34PM +0200, Ahmad Fatoum wrote:
> With recent rework, trusted keys are no longer limited to TPM as trust
> source. The Kconfig symbol is unchanged however leading to a few issues:
>
> - TCG_TPM is required, even if only TEE is to be used
> - Enabling TCG_TPM, but excluding it from available trusted sources
> is not possible
> - TEE=m && TRUSTED_KEYS=y will lead to TEE support being silently
> dropped, which is not the best user experience
>
> Remedy these issues by introducing two new boolean Kconfig symbols:
> TRUSTED_KEYS_TPM and TRUSTED_KEYS_TEE with the appropriate
> dependencies.
>
> Any code depending on the TPM trusted key backend or symbols exported
> by it will now need to explicitly state that it
>
> depends on TRUSTED_KEYS && TRUSTED_KEYS_TPM
>
> The latter to ensure the dependency is built and the former to ensure
> it's reachable for module builds. This currently only affects
> CONFIG_ASYMMETRIC_TPM_KEY_SUBTYPE, so it's fixed up here as well.
>
> Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
> Tested-By: Andreas Rammhold <andreas@rammhold.de>
> Tested-By: Tim Harvey <tharvey@gateworks.com>
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
> v3 -> v4:
> - rebased on top of Andreas' regression fix and pulled it back
> into series
>
> v2 -> v3:
> - factored this patch out as a fix for backporting
>
> v1 -> v2:
> - Move rest of TPM-related selects from TRUSTED_KEYS to
> TRUSTED_KEYS_TPM (Sumit)
> - Remove left-over line in Makefile (Sumit)
> - added Fixes: tag
> - adjust commit message to reference the regression reported
> by Andreas
> - have ASYMMETRIC_TPM_KEY_SUBTYPE depend on TRUSTED_KEYS_TPM,
> because it references global symbols that are exported
> by the trusted key TPM backend.
>
> [1]: https://lore.kernel.org/linux-integrity/f8285eb0135ba30c9d846cf9dd395d1f5f8b1efc.1624364386.git-series.a.fatoum@pengutronix.de/
> [2]: https://lore.kernel.org/linux-integrity/20210719091335.vwfebcpkf4pag3wm@wrt/T/#t
>
> To: Jarkko Sakkinen <jarkko@kernel.org>
> To: James Morris <jmorris@namei.org>
> To: "Serge E. Hallyn" <serge@hallyn.com>
> To: James Bottomley <jejb@linux.ibm.com>
> To: Mimi Zohar <zohar@linux.ibm.com>
> To: Sumit Garg <sumit.garg@linaro.org>
> To: David Howells <dhowells@redhat.com>
> To: Herbert Xu <herbert@gondor.apana.org.au>
> To: "David S. Miller" <davem@davemloft.net>
> Cc: David Gstir <david@sigma-star.at>
> Cc: Richard Weinberger <richard@nod.at>
> Cc: keyrings@vger.kernel.org
> Cc: linux-crypto@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-security-module@vger.kernel.org
> Cc: linux-integrity@vger.kernel.org
> ---
> crypto/asymmetric_keys/Kconfig | 2 +-
> security/keys/Kconfig | 18 +++++----------
> security/keys/trusted-keys/Kconfig | 29 ++++++++++++++++++++++++-
> security/keys/trusted-keys/Makefile | 8 +++----
> security/keys/trusted-keys/trusted_core.c | 4 +--
> 5 files changed, 43 insertions(+), 18 deletions(-)
> create mode 100644 security/keys/trusted-keys/Kconfig
>
> diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
> index 1f1f004dc757..8886eddbf881 100644
> --- a/crypto/asymmetric_keys/Kconfig
> +++ b/crypto/asymmetric_keys/Kconfig
> @@ -25,7 +25,7 @@ config ASYMMETRIC_PUBLIC_KEY_SUBTYPE
> config ASYMMETRIC_TPM_KEY_SUBTYPE
> tristate "Asymmetric TPM backed private key subtype"
> depends on TCG_TPM
> - depends on TRUSTED_KEYS
> + depends on TRUSTED_KEYS && TRUSTED_KEYS_TPM
> select CRYPTO_HMAC
> select CRYPTO_SHA1
> select CRYPTO_HASH_INFO
> diff --git a/security/keys/Kconfig b/security/keys/Kconfig
> index 64b81abd087e..9ec302962fe2 100644
> --- a/security/keys/Kconfig
> +++ b/security/keys/Kconfig
> @@ -70,23 +70,19 @@ config BIG_KEYS
>
> config TRUSTED_KEYS
> tristate "TRUSTED KEYS"
> - depends on KEYS && TCG_TPM
> - select CRYPTO
> - select CRYPTO_HMAC
> - select CRYPTO_SHA1
> - select CRYPTO_HASH_INFO
> - select ASN1_ENCODER
> - select OID_REGISTRY
> - select ASN1
> + depends on KEYS
> help
> This option provides support for creating, sealing, and unsealing
> keys in the kernel. Trusted keys are random number symmetric keys,
> - generated and RSA-sealed by the TPM. The TPM only unseals the keys,
> - if the boot PCRs and other criteria match. Userspace will only ever
> - see encrypted blobs.
> + generated and sealed by a trust source selected at kernel boot-time.
> + Userspace will only ever see encrypted blobs.
>
> If you are unsure as to whether this is required, answer N.
>
> +if TRUSTED_KEYS
> +source "security/keys/trusted-keys/Kconfig"
> +endif
> +
> config ENCRYPTED_KEYS
> tristate "ENCRYPTED KEYS"
> depends on KEYS
> diff --git a/security/keys/trusted-keys/Kconfig b/security/keys/trusted-keys/Kconfig
> new file mode 100644
> index 000000000000..fc4abd581abb
> --- /dev/null
> +++ b/security/keys/trusted-keys/Kconfig
> @@ -0,0 +1,29 @@
> +config TRUSTED_KEYS_TPM
> + bool "TPM-based trusted keys"
> + depends on TCG_TPM >= TRUSTED_KEYS
> + default y
> + select CRYPTO
> + select CRYPTO_HMAC
> + select CRYPTO_SHA1
> + select CRYPTO_HASH_INFO
> + select ASN1_ENCODER
> + select OID_REGISTRY
> + select ASN1
> + help
> + Enable use of the Trusted Platform Module (TPM) as trusted key
> + backend. Trusted keys are random number symmetric keys,
> + which will be generated and RSA-sealed by the TPM.
> + The TPM only unseals the keys, if the boot PCRs and other
> + criteria match.
> +
> +config TRUSTED_KEYS_TEE
> + bool "TEE-based trusted keys"
> + depends on TEE >= TRUSTED_KEYS
> + default y
> + help
> + Enable use of the Trusted Execution Environment (TEE) as trusted
> + key backend.
> +
> +if !TRUSTED_KEYS_TPM && !TRUSTED_KEYS_TEE
> +comment "No trust source selected!"
> +endif
> diff --git a/security/keys/trusted-keys/Makefile b/security/keys/trusted-keys/Makefile
> index feb8b6c3cc79..2e2371eae4d5 100644
> --- a/security/keys/trusted-keys/Makefile
> +++ b/security/keys/trusted-keys/Makefile
> @@ -5,10 +5,10 @@
>
> obj-$(CONFIG_TRUSTED_KEYS) += trusted.o
> trusted-y += trusted_core.o
> -trusted-y += trusted_tpm1.o
> +trusted-$(CONFIG_TRUSTED_KEYS_TPM) += trusted_tpm1.o
>
> $(obj)/trusted_tpm2.o: $(obj)/tpm2key.asn1.h
> -trusted-y += trusted_tpm2.o
> -trusted-y += tpm2key.asn1.o
> +trusted-$(CONFIG_TRUSTED_KEYS_TPM) += trusted_tpm2.o
> +trusted-$(CONFIG_TRUSTED_KEYS_TPM) += tpm2key.asn1.o
>
> -trusted-$(CONFIG_TEE) += trusted_tee.o
> +trusted-$(CONFIG_TRUSTED_KEYS_TEE) += trusted_tee.o
> diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
> index 5b35f1b87644..8cab69e5d0da 100644
> --- a/security/keys/trusted-keys/trusted_core.c
> +++ b/security/keys/trusted-keys/trusted_core.c
> @@ -27,10 +27,10 @@ module_param_named(source, trusted_key_source, charp, 0);
> MODULE_PARM_DESC(source, "Select trusted keys source (tpm or tee)");
>
> static const struct trusted_key_source trusted_key_sources[] = {
> -#if IS_REACHABLE(CONFIG_TCG_TPM)
> +#if defined(CONFIG_TRUSTED_KEYS_TPM)
> { "tpm", &trusted_key_tpm_ops },
> #endif
> -#if IS_REACHABLE(CONFIG_TEE)
> +#if defined(CONFIG_TRUSTED_KEYS_TEE)
> { "tee", &trusted_key_tee_ops },
> #endif
> };
> --
> git-series 0.9.1

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

/Jarkko