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