KEYS: trusted: allow use of kernel RNG for key material

The two existing trusted key sources don't make use of the kernel RNG,
but instead let the hardware doing the sealing/unsealing also
generate the random key material. However, both users and future
backends may want to place less trust into the quality of the trust
source's random number generator and instead reuse the kernel entropy
pool, which can be seeded from multiple entropy sources.

Make this possible by adding a new trusted.rng parameter,
that will force use of the kernel RNG. In its absence, it's up
to the trust source to decide, which random numbers to use,
maintaining the existing behavior.

Suggested-by: Jarkko Sakkinen <jarkko@kernel.org>
Acked-by: Sumit Garg <sumit.garg@linaro.org>
Acked-by: Pankaj Gupta <pankaj.gupta@nxp.com>
Reviewed-by: David Gstir <david@sigma-star.at>
Reviewed-by: Pankaj Gupta <pankaj.gupta@nxp.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Pankaj Gupta <pankaj.gupta@nxp.com>
Tested-by: Michael Walle <michael@walle.cc> # on ls1028a (non-E and E)
Tested-by: John Ernberg <john.ernberg@actia.se> # iMX8QXP
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 3f1cc5e317ed4a5ad001082c9c589b6008f68db9..4deed1908a75718b57674ff06ae2bb062e2090ba 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5963,6 +5963,16 @@
                        first trust source as a backend which is initialized
                        successfully during iteration.
 
+       trusted.rng=    [KEYS]
+                       Format: <string>
+                       The RNG used to generate key material for trusted keys.
+                       Can be one of:
+                       - "kernel"
+                       - the same value as trusted.source: "tpm" or "tee"
+                       - "default"
+                       If not specified, "default" is used. In this case,
+                       the RNG's choice is left to each individual trust source.
+
        tsc=            Disable clocksource stability checks for TSC.
                        Format: <string>
                        [x86] reliable: mark tsc clocksource as reliable, this

diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
index f614dad7de12f90aec85b32955986bd76126a39f..2fe6fd1a2bbd1ee886a4dc3b5b238fcb88175639 100644 (file)
--- a/Documentation/security/keys/trusted-encrypted.rst
+++ b/Documentation/security/keys/trusted-encrypted.rst
@@ -87,22 +87,26 @@ Key Generation
 Trusted Keys
 ------------
 
-New keys are created from random numbers generated in the trust source. They
-are encrypted/decrypted using a child key in the storage key hierarchy.
-Encryption and decryption of the child key must be protected by a strong
-access control policy within the trust source.
+New keys are created from random numbers. They are encrypted/decrypted using
+a child key in the storage key hierarchy. Encryption and decryption of the
+child key must be protected by a strong access control policy within the
+trust source. The random number generator in use differs according to the
+selected trust source:
 
-  *  TPM (hardware device) based RNG
+  *  TPM: hardware device based RNG
 
-     Strength of random numbers may vary from one device manufacturer to
-     another.
+     Keys are generated within the TPM. Strength of random numbers may vary
+     from one device manufacturer to another.
 
-  *  TEE (OP-TEE based on Arm TrustZone) based RNG
+  *  TEE: OP-TEE based on Arm TrustZone based RNG
 
      RNG is customizable as per platform needs. It can either be direct output
      from platform specific hardware RNG or a software based Fortuna CSPRNG
      which can be seeded via multiple entropy sources.
 
+Users may override this by specifying ``trusted.rng=kernel`` on the kernel
+command-line to override the used RNG with the kernel's random number pool.
+
 Encrypted Keys
 --------------
 

diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
index d89fa2579ac0569864508ef4d175669f22314d35..4eb64548a74f1ad0b636a8caa35cb8b4544f573e 100644 (file)
--- a/include/keys/trusted-type.h
+++ b/include/keys/trusted-type.h
@@ -64,7 +64,7 @@ struct trusted_key_ops {
        /* Unseal a key. */
        int (*unseal)(struct trusted_key_payload *p, char *datablob);
 
-       /* Get a randomized key. */
+       /* Optional: Get a randomized key. */
        int (*get_random)(unsigned char *key, size_t key_len);
 
        /* Exit key interface. */

diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
index 7cdbd16aed30b9b51916ddc6b72f4bfc8a6f82a1..9235fb7d0ec970deba5f432d891639056121478d 100644 (file)
--- a/security/keys/trusted-keys/trusted_core.c
+++ b/security/keys/trusted-keys/trusted_core.c
@@ -16,12 +16,17 @@
 #include <linux/key-type.h>
 #include <linux/module.h>
 #include <linux/parser.h>
+#include <linux/random.h>
 #include <linux/rcupdate.h>
 #include <linux/slab.h>
 #include <linux/static_call.h>
 #include <linux/string.h>
 #include <linux/uaccess.h>
 
+static char *trusted_rng = "default";
+module_param_named(rng, trusted_rng, charp, 0);
+MODULE_PARM_DESC(rng, "Select trusted key RNG");
+
 static char *trusted_key_source;
 module_param_named(source, trusted_key_source, charp, 0);
 MODULE_PARM_DESC(source, "Select trusted keys source (tpm or tee)");
@@ -312,8 +317,14 @@ struct key_type key_type_trusted = {
 };
 EXPORT_SYMBOL_GPL(key_type_trusted);
 
+static int kernel_get_random(unsigned char *key, size_t key_len)
+{
+       return get_random_bytes_wait(key, key_len) ?: key_len;
+}
+
 static int __init init_trusted(void)
 {
+       int (*get_random)(unsigned char *key, size_t key_len);
        int i, ret = 0;
 
        for (i = 0; i < ARRAY_SIZE(trusted_key_sources); i++) {
@@ -322,6 +333,28 @@ static int __init init_trusted(void)
                            strlen(trusted_key_sources[i].name)))
                        continue;
 
+               /*
+                * We always support trusted.rng="kernel" and "default" as
+                * well as trusted.rng=$trusted.source if the trust source
+                * defines its own get_random callback.
+                */
+               get_random = trusted_key_sources[i].ops->get_random;
+               if (trusted_rng && strcmp(trusted_rng, "default")) {
+                       if (!strcmp(trusted_rng, "kernel")) {
+                               get_random = kernel_get_random;
+                       } else if (strcmp(trusted_rng, trusted_key_sources[i].name) ||
+                                  !get_random) {
+                               pr_warn("Unsupported RNG. Supported: kernel");
+                               if (get_random)
+                                       pr_cont(", %s", trusted_key_sources[i].name);
+                               pr_cont(", default\n");
+                               return -EINVAL;
+                       }
+               }
+
+               if (!get_random)
+                       get_random = kernel_get_random;
+
                static_call_update(trusted_key_init,
                                   trusted_key_sources[i].ops->init);
                static_call_update(trusted_key_seal,
@@ -329,7 +362,7 @@ static int __init init_trusted(void)
                static_call_update(trusted_key_unseal,
                                   trusted_key_sources[i].ops->unseal);
                static_call_update(trusted_key_get_random,
-                                  trusted_key_sources[i].ops->get_random);
+                                  get_random);
                static_call_update(trusted_key_exit,
                                   trusted_key_sources[i].ops->exit);
                migratable = trusted_key_sources[i].ops->migratable;