[PATCH 3/3] integrity: Load keys from TPM NV onto IMA keyring

[Patrick Uiterwijk <patrick@puiterwijk.org>]

Allows users to enroll their own public key stored in a specific TPM2
NV Index, requiring the absence of the Platform Create and Platform
Write attributes on the NV Index, to be loaded on the IMA keyring.

Provides a method for users to load keys without the need to recompile
the kernel or change the kernel binary, which would require a resign of
the kernel image.

Signed-off-by: Patrick Uiterwijk <patrick@puiterwijk.org>
---
 security/integrity/ima/Kconfig    | 22 +++++++++++++
 security/integrity/ima/ima_init.c | 53 +++++++++++++++++++++++++++++++
 2 files changed, 75 insertions(+)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 12e9250c1bec..28424b930c81 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -291,6 +291,28 @@ config IMA_BLACKLIST_KEYRING
 	   the search is successful the requested operation is rejected and
 	   an error is returned to the caller.
 
+config IMA_LOAD_CERT_NVINDEX
+	bool "Load certificate from TPM nvindex into '.ima' trusted keyring"
+	depends on IMA_TRUSTED_KEYRING && TCG_TPM
+	default n
+	help
+	   File signature verification is based on the public keys
+	   loaded on the .ima trusted keyring. These public keys are
+	   X509 certificates signed by a trusted key on the
+	   .system keyring.  This option enables X509 certificate
+	   loading by the kernel onto the '.ima' trusted keyring
+	   from a TPM nvindex, bypassing the builtin keyring check.
+
+config IMA_LOAD_CERT_NVINDEX_INDEX
+	hex "The TPM NV Index to load into the '.ima' trusted keyring"
+	depends on IMA_LOAD_CERT_NVINDEX
+	default 0x184b520
+	help
+	   Defines the index of the NV Index that gets loaded into the
+	   '.ima' keyring.
+	   The default is the "0x18" prefix for a non-TCG specified NV Index,
+	   suffixed with ASCII for "KR" (keyring) and then 0
+
 config IMA_LOAD_X509
 	bool "Load X509 certificate onto the '.ima' trusted keyring"
 	depends on IMA_TRUSTED_KEYRING
diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
index 6e8742916d1d..ea0949e8df12 100644
--- a/security/integrity/ima/ima_init.c
+++ b/security/integrity/ima/ima_init.c
@@ -112,6 +112,55 @@ void __init ima_load_x509(void)
 }
 #endif
 
+#ifndef CONFIG_IMA_LOAD_CERT_NVINDEX
+int __init ima_load_key_nvindex(void)
+{
+	return 0;
+}
+#else
+int __init ima_load_key_nvindex(void)
+{
+	void *cert_buffer;
+	int rc;
+	key_perm_t perm;
+	u32 nvindex_attributes = 0;
+
+	rc = tpm_nv_read(tpm_default_chip(),
+				CONFIG_IMA_LOAD_CERT_NVINDEX_INDEX,
+				&nvindex_attributes, &cert_buffer);
+	if (rc < 0) {
+		if (rc == -ENODEV)  /* No TPM2 */
+			rc = 0;
+		if (rc == -ENOENT)  /* No certificate in NV Index */
+			rc = 0;
+		goto out;
+	}
+
+	pr_info("Loading IMA key from TPM NV Index 0x%x", CONFIG_IMA_LOAD_CERT_NVINDEX_INDEX);
+
+	if (nvindex_attributes & TPM2_ATTR_NV_PLATFORMCREATE) {
+		pr_err("NV Index has the Platform Create attribute");
+		rc = -EACCES;
+		goto out_free;
+	}
+	if (nvindex_attributes & TPM2_ATTR_NV_PPWRITE) {
+		pr_err("NV Index has the Platform Write attribute");
+		rc = -EACCES;
+		goto out_free;
+	}
+
+	perm = (KEY_POS_ALL & ~KEY_POS_SETATTR) | KEY_USR_VIEW | KEY_USR_READ;
+	rc = integrity_load_cert(INTEGRITY_KEYRING_IMA, "TPM NV Index",
+				 cert_buffer, rc, perm,
+				 KEY_ALLOC_BYPASS_RESTRICTION);
+
+out_free:
+	kvfree(cert_buffer);
+out:
+	return rc;
+}
+#endif
+
 int __init ima_init(void)
 {
 	int rc;
@@ -124,6 +173,10 @@ int __init ima_init(void)
 	if (rc)
 		return rc;
 
+	rc = ima_load_key_nvindex();
+	if (rc)
+		pr_info("Failed to load IMA key from TPM NV Index (%d)", rc);
+
 	rc = ima_init_crypto();
 	if (rc)
 		return rc;
-- 
2.29.2