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Message-ID: <20210721201730.ht75blv5pd7qgyep@wrt>
Date: Wed, 21 Jul 2021 22:17:30 +0200
From: Andreas Rammhold <andreas@...mhold.de>
To: Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc: Jarkko Sakkinen <jarkko@...nel.org>,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
James Bottomley <jejb@...ux.ibm.com>,
Mimi Zohar <zohar@...ux.ibm.com>,
Sumit Garg <sumit.garg@...aro.org>,
David Howells <dhowells@...hat.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>, kernel@...gutronix.de,
Andreas Rammhold <andreas@...mhold.de>,
David Gstir <david@...ma-star.at>,
Richard Weinberger <richard@....at>, keyrings@...r.kernel.org,
linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-integrity@...r.kernel.org
Subject: Re: [PATCH v2] KEYS: trusted: fix use as module when CONFIG_TCG_TPM=m
On 18:02 21.07.21, Ahmad Fatoum wrote:
> Since commit 5d0682be3189 ("KEYS: trusted: Add generic trusted keys
> framework"), trusted.ko built with CONFIG_TCG_TPM=CONFIG_TRUSTED_KEYS=m
> will not register the TPM trusted key type at runtime.
>
> This is because, after that rework, CONFIG_DEPENDENCY of the TPM
> and TEE backends were checked with #ifdef, but that's only true
> when they're built-in.
>
> Fix this by introducing two new boolean Kconfig symbols:
> TRUSTED_KEYS_TPM and TRUSTED_KEYS_TEE with the appropriate
> dependencies and use them to check which backends are available.
>
> This also has a positive effect on user experience:
>
> - It's now possible to use TEE trusted keys without CONFIG_TCG_TPM
> - It's now possible to enable CONFIG_TCG_TPM, but exclude TPM from
> available trust sources
> - TEE=m && TRUSTED_KEYS=y no longer leads to TEE support
> being silently dropped
>
> 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.
>
> Reported-by: Andreas Rammhold <andreas@...mhold.de>
> Fixes: 5d0682be3189 ("KEYS: trusted: Add generic trusted keys framework")
> Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
> ---
>
> (Implicit) v1 was as a preparatory patch for CAAM trusted keys[1] with the
> goal of fixing the Kconfig inflexibility after the TEE trusted key rework.
>
> Unbeknownst to me, it also fixes a regression, which was later
> reported by Andreas[2] along with a patch.
>
> I split out the fix from the CAAM series and adjusted the commit
> message to explain the regression.
>
> 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@...nel.org>
> To: James Morris <jmorris@...ei.org>
> To: "Serge E. Hallyn" <serge@...lyn.com>
> To: James Bottomley <jejb@...ux.ibm.com>
> To: Mimi Zohar <zohar@...ux.ibm.com>
> To: Sumit Garg <sumit.garg@...aro.org>
> To: David Howells <dhowells@...hat.com>
> To: Herbert Xu <herbert@...dor.apana.org.au>
> To: "David S. Miller" <davem@...emloft.net>
> Cc: David Gstir <david@...ma-star.at>
> Cc: Richard Weinberger <richard@....at>
> Cc: keyrings@...r.kernel.org
> Cc: linux-crypto@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-security-module@...r.kernel.org
> Cc: linux-integrity@...r.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..c163cfeedff6
> --- /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 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 d5c891d8d353..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 defined(CONFIG_TCG_TPM)
> +#if defined(CONFIG_TRUSTED_KEYS_TPM)
> { "tpm", &trusted_key_tpm_ops },
> #endif
> -#if defined(CONFIG_TEE)
> +#if defined(CONFIG_TRUSTED_KEYS_TEE)
> { "tee", &trusted_key_tee_ops },
> #endif
> };
> --
> 2.30.2
>
Works like a charm here. The key type was registered even thought I
built the kernel with CONFIG_TRUSTED_KEYS=m.
I've not actually tested if that key type works (as I've not progressed
that far in my toy project just yet).
Feel free to add my Test-By.
Tested-By: Andreas Rammhold <andreas@...mhold.de>
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