commit 5c7482104f61d43b15f8421c3a5c546d16d0cd45
author Janis Danisevskis <jdanis@google.com> Mon May 17 17:13:56 2021 -0700
committer Janis Danisevskis <jdanis@google.com> Tue Jun 01 14:30:27 2021 -0700
tree 33996d0771da7ed25f86b6ddbd5875b65eb13371
parent 67f30564f44fa0b6c6e4e1b93b89f89b01f2d29e

Keystore 2.0: Use preferred KM instance for level zero key.

Prefer KM4.1 and higher over KM4.0 and lower, but prefer TEE over
Strongbox if TEE meets the minimal requirements.

Ignore-AOSP-First: No automerge path from AOSP.
Bug: 187862706
Test: Manually tested by observing logs during boot.
Merged-In: I1d27c80ef7c869b84b6d0c1a5d8eec287c242f6c
Change-Id: I1d27c80ef7c869b84b6d0c1a5d8eec287c242f6c
Merged-In: I1d27c80ef7c869b84b6d0c1a5d8eec287c242f6c

keystore2/src/boot_level_keys.rs

diff --git a/keystore2/src/boot_level_keys.rs b/keystore2/src/boot_level_keys.rs
index 3084195..5b7c3c3 100644
--- a/keystore2/src/boot_level_keys.rs
+++ b/keystore2/src/boot_level_keys.rs
@@ -14,6 +14,7 @@
 
 //! Offer keys based on the "boot level" for superencryption.
 
+use crate::{database::KeystoreDB, key_parameter::KeyParameterValue, raw_device::KeyMintDevice};
 use android_hardware_security_keymint::aidl::android::hardware::security::keymint::{
     Algorithm::Algorithm, Digest::Digest, KeyPurpose::KeyPurpose, SecurityLevel::SecurityLevel,
 };
@@ -21,26 +22,46 @@
 use keystore2_crypto::{hkdf_expand, ZVec, AES_256_KEY_LENGTH};
 use std::{collections::VecDeque, convert::TryFrom};
 
-use crate::{database::KeystoreDB, key_parameter::KeyParameterValue, raw_device::KeyMintDevice};
+fn get_preferred_km_instance_for_level_zero_key() -> Result<KeyMintDevice> {
+    let tee = KeyMintDevice::get(SecurityLevel::TRUSTED_ENVIRONMENT)
+        .context("In get_preferred_km_instance_for_level_zero_key: Get TEE instance failed.")?;
+    if tee.version() >= KeyMintDevice::KEY_MASTER_V4_1 {
+        Ok(tee)
+    } else {
+        match KeyMintDevice::get_or_none(SecurityLevel::STRONGBOX).context(
+            "In get_preferred_km_instance_for_level_zero_key: Get Strongbox instance failed.",
+        )? {
+            Some(strongbox) if strongbox.version() >= KeyMintDevice::KEY_MASTER_V4_1 => {
+                Ok(strongbox)
+            }
+            _ => Ok(tee),
+        }
+    }
+}
 
 /// This is not thread safe; caller must hold a lock before calling.
 /// In practice the caller is SuperKeyManager and the lock is the
 /// Mutex on its internal state.
 pub fn get_level_zero_key(db: &mut KeystoreDB) -> Result<ZVec> {
+    let km_dev = get_preferred_km_instance_for_level_zero_key()
+        .context("In get_level_zero_key: get preferred KM instance failed")?;
+
     let key_desc = KeyMintDevice::internal_descriptor("boot_level_key".to_string());
-    let params = [
+    let mut params = vec![
         KeyParameterValue::Algorithm(Algorithm::HMAC).into(),
         KeyParameterValue::Digest(Digest::SHA_2_256).into(),
         KeyParameterValue::KeySize(256).into(),
         KeyParameterValue::MinMacLength(256).into(),
         KeyParameterValue::KeyPurpose(KeyPurpose::SIGN).into(),
         KeyParameterValue::NoAuthRequired.into(),
-        KeyParameterValue::MaxUsesPerBoot(1).into(),
     ];
-    // We use TRUSTED_ENVIRONMENT here because it is the authority on when
-    // the device has rebooted.
-    let km_dev: KeyMintDevice = KeyMintDevice::get(SecurityLevel::TRUSTED_ENVIRONMENT)
-        .context("In get_level_zero_key: KeyMintDevice::get failed")?;
+
+    if km_dev.version() >= KeyMintDevice::KEY_MASTER_V4_1 {
+        params.push(KeyParameterValue::EarlyBootOnly.into());
+    } else {
+        params.push(KeyParameterValue::MaxUsesPerBoot(1).into())
+    }
+
     let (key_id_guard, key_entry) = km_dev
         .lookup_or_generate_key(db, &key_desc, &params)
         .context("In get_level_zero_key: lookup_or_generate_key failed")?;