From 7f7a9b19c8293c09dfee12bec75ff17225c6710e Mon Sep 17 00:00:00 2001 From: Danny Lin Date: Tue, 12 Jan 2021 22:25:13 -0800 Subject: [PATCH] KeyStore: Block key attestation for Google Play Services In order to enforce SafetyNet security, Google Play Services is now using hardware attestation for ctsProfile validation in all cases, even when basic attestation is selected. The SafetyNet API response from GMS will report that basic attestation was used, but under the hood, hardware attestation is always used regardless of the reported state. This results in SafetyNet failing to pass due to TrustZone reporting an unlocked bootloader (and a partially invalidated root of trust) in the key attestation result. We can still take advantage of the fact that this usage of hardware attestation is opportunistic - that is, it falls back to basic attestation if key attestation fails to run - and prevent GMS from using key attestation at the framework level. This causes it to gracefully fall back to basic attestation and pass SafetyNet with an unlocked bootloader. Key attestation is still available for other apps, as there are valid uses for it that do not involve SafetyNet. The "not implemented" error code from keymaster is used to simulate the most realistic failure condition to evade detection, i.e. an old device that lacks support for key attestation. Change-Id: I7282ab22b933434bb11037743d46b8a20dad063a --- keystore/java/android/security/KeyStore.java | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/keystore/java/android/security/KeyStore.java b/keystore/java/android/security/KeyStore.java index 88b614dc7eef..0f766ef738bf 100644 --- a/keystore/java/android/security/KeyStore.java +++ b/keystore/java/android/security/KeyStore.java @@ -1124,6 +1124,11 @@ public class KeyStore { public int attestKey( String alias, KeymasterArguments params, KeymasterCertificateChain outChain) { + // Prevent Google Play Services from using key attestation for SafetyNet + if (mContext.getPackageName().equals("com.google.android.gms")) { + return KeymasterDefs.KM_ERROR_UNIMPLEMENTED; + } + CertificateChainPromise promise = new CertificateChainPromise(); try { mBinder.asBinder().linkToDeath(promise, 0); -- 2.29.2