Handle keystore2 blob prefixes
The keystore2 km_compat layer that wraps Keymaster hardware
implementations prefixes the Keymaster blobs with some magic and an
indicator value. When Keymaster is upgraded in-place to KeyMint,
keystore2 will stop using km_compat and pass the prefixed blobs to
KeyMint as-is. This change causes Trusty KeyMint to look for and
strip those prefixes.
Bug: 177729159
Test: Manually create keys, update HAL and verify keys work
Change-Id: I5a7f322206bce1c5a384666fa3200afaa62f1f5a
diff --git a/trusty_keymaster_context.cpp b/trusty_keymaster_context.cpp
index aded6a7..d2e978a 100644
--- a/trusty_keymaster_context.cpp
+++ b/trusty_keymaster_context.cpp
@@ -15,11 +15,8 @@
*/
#include "trusty_keymaster_context.h"
-#include "secure_storage_manager.h"
-#include <lib/hwkey/hwkey.h>
-#include <lib/rng/trusty_rng.h>
-#include <openssl/hmac.h>
+#include <array>
#include <keymaster/android_keymaster_utils.h>
#include <keymaster/contexts/soft_attestation_cert.h>
@@ -37,7 +34,11 @@
#include <keymaster/logger.h>
#include <keymaster/operation.h>
#include <keymaster/wrapped_key.h>
+#include <lib/hwkey/hwkey.h>
+#include <lib/rng/trusty_rng.h>
+#include <openssl/hmac.h>
+#include "secure_storage_manager.h"
#include "trusty_aes_key.h"
#ifdef KEYMASTER_DEBUG
@@ -378,6 +379,11 @@
upgraded_key);
}
+constexpr std::array<uint8_t, 7> kKeystoreKeyBlobMagic = {'p', 'K', 'M', 'b',
+ 'l', 'o', 'b'};
+constexpr size_t kKeystoreKeyTypeOffset = kKeystoreKeyBlobMagic.size();
+constexpr size_t kKeystoreKeyBlobPrefixSize = kKeystoreKeyTypeOffset + 1;
+
keymaster_error_t TrustyKeymasterContext::ParseKeyBlob(
const KeymasterKeyBlob& blob,
const AuthorizationSet& additional_params,
@@ -388,8 +394,49 @@
if (!key) {
return KM_ERROR_UNEXPECTED_NULL_POINTER;
}
- DeserializedKey deserialized_key =
- DeserializeAuthEncryptedBlob(blob, &error);
+
+ DeserializedKey deserialized_key;
+ if (blob.size() >= kKeystoreKeyBlobPrefixSize &&
+ std::equal(kKeystoreKeyBlobMagic.begin(), kKeystoreKeyBlobMagic.end(),
+ blob.begin())) {
+ // This blob has a keystore km_compat prefix. This means that it was
+ // created by keystore calling TrustyKeymaster through the km_compat
+ // layer. The km_compat layer adds this prefix to determine whether
+ // it's actually a hardware blob that should be passed through to
+ // Keymaster, or whether it's a software only key and should be used by
+ // the emulation layer.
+ //
+ // In the case of hardware blobs, km_compat strips the prefix before
+ // handing the blob to Keymaster. In the case of software blobs,
+ // km_compat never hands the blob to Keymaster.
+ //
+ // The fact that we've received this prefixed blob means that it was
+ // created through km_compat... but the device has now been upgraded
+ // from TrustyKeymaster to TrustyKeyMint, and so keystore is no longer
+ // using the km_compat layer, and the blob is just passed through with
+ // its prefix intact.
+ auto keyType = *(blob.begin() + kKeystoreKeyTypeOffset);
+ switch (keyType) {
+ case 0:
+ LOG_E("Software key blobs are not supported.", 0);
+ return KM_ERROR_INVALID_KEY_BLOB;
+
+ case 1:
+ // This is a hardware blob. Strip the prefix and use the blob.
+ deserialized_key = DeserializeAuthEncryptedBlob(
+ KeymasterKeyBlob(blob.begin() + kKeystoreKeyBlobPrefixSize,
+ blob.size() - kKeystoreKeyBlobPrefixSize),
+ &error);
+ break;
+
+ default:
+ LOG_E("Invalid keystore blob prefix value %d", keyType);
+ return KM_ERROR_INVALID_KEY_BLOB;
+ }
+ } else {
+ deserialized_key = DeserializeAuthEncryptedBlob(blob, &error);
+ }
+
if (error != KM_ERROR_OK) {
return error;
}
