On 2/25/21 3:32 PM, Patrick Uiterwijk wrote:
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@xxxxxxxxxxxxxx>
---
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(),
You should do chip = tpm_default_chip() so that later on you can do
put_device(&chip->dev).
+ 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);
kfree?
+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;
