[PATCH v6 1/4] KEYS: trusted: allow use of TEE as backend without TCG_TPM support

Wed Mar 16 16:43:32 UTC 2022

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 new code depending on the TPM trusted key backend in particular
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. There are no such users yet.

Reviewed-by: Sumit Garg <sumit.garg at linaro.org>
Reviewed-by: Jarkko Sakkinen <jarkko at kernel.org>
Tested-By: Andreas Rammhold <andreas at rammhold.de>
Tested-By: Tim Harvey <tharvey at gateworks.com>
Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
v5 -> v6:
  - Rebased on asym_tpm removal
v4 -> v5:
  - collected Jarkko's Reviewed-by
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 at kernel.org>
To: James Morris <jmorris at namei.org>
To: "Serge E. Hallyn" <serge at hallyn.com>
To: James Bottomley <jejb at linux.ibm.com>
To: Mimi Zohar <zohar at linux.ibm.com>
To: Sumit Garg <sumit.garg at linaro.org>
To: David Howells <dhowells at redhat.com>
To: Herbert Xu <herbert at gondor.apana.org.au>
To: "David S. Miller" <davem at davemloft.net>
Cc: David Gstir <david at sigma-star.at>
Cc: Richard Weinberger <richard at nod.at>
Cc: Matthias Schiffer <matthias.schiffer at ew.tq-group.com>
Cc: keyrings at vger.kernel.org
Cc: linux-crypto at vger.kernel.org
Cc: linux-kernel at vger.kernel.org
Cc: linux-security-module at vger.kernel.org
Cc: linux-integrity at vger.kernel.org
---
 security/keys/Kconfig                     | 18 ++++++--------
 security/keys/trusted-keys/Kconfig        | 29 +++++++++++++++++++++++
 security/keys/trusted-keys/Makefile       |  8 +++----
 security/keys/trusted-keys/trusted_core.c |  4 ++--
 4 files changed, 42 insertions(+), 17 deletions(-)
 create mode 100644 security/keys/trusted-keys/Kconfig

diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index 969122c7b92f..826cd0904f9a 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 9b9d3ef79cbe..7cdbd16aed30 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
 };
-- 
2.30.2

