From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Tad <tad@spotco.us>
Date: Mon, 3 Jul 2023 12:00:12 -0400
Subject: [PATCH] Hardened signature spoofing

- Must be enabled by user
- Must match microG package ID
- Must meet minimum respective targetSdk and versionCode
- Must match official microG build signing key
- Only spoofs the Google package signature

This is an effective merge + tweak of two existing patches, credits:
  Dylanger Daly
  https://github.com/dylangerdaly/platform_frameworks_base/commit/b58aa11631fadab3309a1d9268118bd9f2c2a79f
  Chirayu Desai of CalyxOS
  https://gitlab.com/CalyxOS/platform_frameworks_base/-/commit/76485abb36dc01b65506b010d0458e96e0116369

Change-Id: I64a252aac9bb196a11ed7b4b5d8c7e59a3413bd4
---
 .../android/content/pm/PackageParser.java     | 32 +++++++++++++++
 core/res/res/values/config.xml                |  2 +
 .../server/pm/PackageManagerService.java      | 39 ++++++++++++++++++-
 3 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/core/java/android/content/pm/PackageParser.java b/core/java/android/content/pm/PackageParser.java
index f9f3ead23fb8..1da73e46f81d 100644
--- a/core/java/android/content/pm/PackageParser.java
+++ b/core/java/android/content/pm/PackageParser.java
@@ -6348,6 +6348,38 @@ public class PackageParser {
             return false;
         }
 
+        /**
+         * Return the Cerificate's Digest
+         */
+        public @Nullable String getSha256Certificate() {
+            return getSha256CertificateInternal();
+        }
+
+        private @Nullable String getSha256CertificateInternal() {
+            String digest;
+            if (this == UNKNOWN) {
+                return null;
+            }
+            if (hasPastSigningCertificates()) {
+
+                // check all past certs, except for the last one, which automatically gets all
+                // capabilities, since it is the same as the current signature, and is checked below
+                for (int i = 0; i < pastSigningCertificates.length - 1; i++) {
+                    digest = PackageUtils.computeSha256Digest(
+                            pastSigningCertificates[i].toByteArray());
+                    return digest;
+                }
+            }
+
+            // not in previous certs signing history, just check the current signer
+            if (signatures.length == 1) {
+                digest =
+                        PackageUtils.computeSha256Digest(signatures[0].toByteArray());
+                return digest;
+            }
+            return null;
+        }
+
         /** Returns true if the signatures in this and other match exactly. */
         public boolean signaturesMatchExactly(SigningDetails other) {
             return Signature.areExactMatch(this.signatures, other.signatures);
diff --git a/core/res/res/values/config.xml b/core/res/res/values/config.xml
index a84d23b624bf..1ab293758ee7 100644
--- a/core/res/res/values/config.xml
+++ b/core/res/res/values/config.xml
@@ -1875,6 +1875,8 @@
     <string-array name="config_locationProviderPackageNames" translatable="false">
         <!-- The standard AOSP fused location provider -->
         <item>com.android.location.fused</item>
+        <!-- The (faked) microg fused location provider (a free reimplementation)
+        <item>com.google.android.gms</item> -->
     </string-array>
 
     <!-- This string array can be overriden to enable test location providers initially. -->
diff --git a/services/core/java/com/android/server/pm/PackageManagerService.java b/services/core/java/com/android/server/pm/PackageManagerService.java
index 9483f266b1fa..7e5a46cfd72f 100644
--- a/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -4203,8 +4203,20 @@ public class PackageManagerService extends IPackageManager.Stub
                 });
             }
 
-            PackageInfo packageInfo = PackageParser.generatePackageInfo(p, gids, flags,
-                    ps.firstInstallTime, ps.lastUpdateTime, permissions, state, userId);
+            // Allow microG GmsCore and FakeStore to spoof signature
+            final boolean isValidGmsCore = p.packageName.equals("com.google.android.gms") && p.applicationInfo.targetSdkVersion >= 29 && p.applicationInfo.versionCode >= 231657056;
+            final boolean isValidFakeStore = p.packageName.equals("com.android.vending") && p.applicationInfo.targetSdkVersion >= 24 && p.applicationInfo.versionCode >= 30;
+            final boolean isMicroG = isValidGmsCore || isValidFakeStore;
+            PackageInfo packageInfo;
+            if (isMicroG && SystemProperties.getBoolean(SPOOF_CONTROL, false)) {
+                packageInfo = fakeSignature(p, PackageParser.generatePackageInfo(p, gids, flags,
+                        ps.firstInstallTime, ps.lastUpdateTime, permissions, state,
+                        userId), permissions);
+            } else {
+                packageInfo =PackageParser.generatePackageInfo(p, gids, flags,
+                        ps.firstInstallTime, ps.lastUpdateTime, permissions, state,
+                        userId);
+            }
 
             if (packageInfo == null) {
                 return null;
@@ -4240,6 +4252,29 @@ public class PackageManagerService extends IPackageManager.Stub
         }
     }
 
+    // The setting to control spoofing enablement.
+    private static final String SPOOF_CONTROL = "persist.security.sigspoof";
+    // The Google signature faked by microG.
+    private static final String GOOGLE_CERT = "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";
+   // The signing key hash of official microG builds.
+    private static final String MICROG_HASH = "9BD06727E62796C0130EB6DAB39B73157451582CBD138E86C468ACC395D14165";
+
+    private PackageInfo fakeSignature(PackageParser.Package p, PackageInfo pi,
+            Set<String> permissions) {
+        String hash = p.mSigningDetails.getSha256Certificate();
+        try {
+            if (hash.equals(MICROG_HASH) && p.applicationInfo.targetSdkVersion >= 24) {
+                    pi.signatures = new Signature[] {new Signature(GOOGLE_CERT)};
+                    if (DEBUG_PACKAGE_INFO) {
+                        Log.v(TAG, "Spoofing signature for microG");
+                    }
+            }
+        } catch (Throwable t) {
+            Log.w("Unable to fake signature!", t);
+        }
+        return pi;
+    }
+
     @Override
     public void checkPackageStartable(String packageName, int userId) {
         final int callingUid = Binder.getCallingUid();
