Disable XOM on libraries for apps with targetSdkVerison<Q

Apps may (and do) assume that libraries are readable. To avoid app
breakage, mark execute-only sections of as read+execute
for apps with targetSdkVersion<Q.

Bug: 128907672
Test: Check libc for app with targetSdk==current
cat /proc/25950/maps | grep libc.so
77c01e3000-77c028b000 --xp 00041000 07:20 106 /apex/com.android.runtime/lib64/bionic/libc.so
Test: Check libc for app with targetSdk<current
cat /proc/26355/maps | grep libc.so
77c01e3000-77c028b000 r-xp 00041000 07:20 106
/apex/com.android.runtime/lib64/bionic/libc.so

Change-Id: I90b5c91923c8008ae4b4818985842fe3e354a850

core/java/com/android/internal/os/Zygote.java

@@ -24,6 +24,7 @@ import android.content.pm.ApplicationInfo;
 import android.net.Credentials;
 import android.net.LocalServerSocket;
 import android.net.LocalSocket;
+import android.os.Build;
 import android.os.FactoryTest;
 import android.os.IVold;
 import android.os.Process;
@@ -236,7 +237,7 @@ public final class Zygote {
     public static int forkAndSpecialize(int uid, int gid, int[] gids, int runtimeFlags,
             int[][] rlimits, int mountExternal, String seInfo, String niceName, int[] fdsToClose,
             int[] fdsToIgnore, boolean startChildZygote, String instructionSet, String appDataDir,
-            String packageName, String[] packagesForUID, String sandboxId) {
+            String packageName, String[] packagesForUID, String sandboxId, int targetSdkVersion) {
         ZygoteHooks.preFork();
         // Resets nice priority for zygote process.
         resetNicePriority();
@@ -246,6 +247,7 @@ public final class Zygote {
                 packagesForUID, sandboxId);
         // Enable tracing as soon as possible for the child process.
         if (pid == 0) {
+            Zygote.disableExecuteOnly(targetSdkVersion);
             Trace.setTracingEnabled(true, runtimeFlags);
 
             // Note that this event ends at the end of handleChildProc,
@@ -599,6 +601,8 @@ public final class Zygote {
                            args.mInstructionSet, args.mAppDataDir, args.mPackageName,
                            args.mPackagesForUid, args.mSandboxId);
 
+        disableExecuteOnly(args.mTargetSdkVersion);
+
         if (args.mNiceName != null) {
             Process.setArgV0(args.mNiceName);
         }
@@ -649,6 +653,17 @@ public final class Zygote {
         }
     }
 
+    /**
+     * Mark execute-only segments of libraries read+execute for apps with targetSdkVersion<Q.
+     */
+    protected static void disableExecuteOnly(int targetSdkVersion) {
+        if ((targetSdkVersion < Build.VERSION_CODES.Q) && !nativeDisableExecuteOnly()) {
+            Log.e("Zygote", "Failed to set libraries to read+execute.");
+        }
+    }
+
+    private static native boolean nativeDisableExecuteOnly();
+
     /**
      * @return  Raw file descriptors for the read-end of USAP reporting pipes.
      */

core/java/com/android/internal/os/ZygoteConnection.java

@@ -264,7 +264,7 @@ class ZygoteConnection {
                 parsedArgs.mRuntimeFlags, rlimits, parsedArgs.mMountExternal, parsedArgs.mSeInfo,
                 parsedArgs.mNiceName, fdsToClose, fdsToIgnore, parsedArgs.mStartChildZygote,
                 parsedArgs.mInstructionSet, parsedArgs.mAppDataDir, parsedArgs.mPackageName,
-                parsedArgs.mPackagesForUid, parsedArgs.mSandboxId);
+                parsedArgs.mPackagesForUid, parsedArgs.mSandboxId, parsedArgs.mTargetSdkVersion);
 
         try {
             if (pid == 0) {

core/jni/com_android_internal_os_Zygote.cpp

@@ -46,6 +46,7 @@
 #include <fcntl.h>
 #include <grp.h>
 #include <inttypes.h>
+#include <link.h>
 #include <malloc.h>
 #include <mntent.h>
 #include <paths.h>
@@ -54,6 +55,7 @@
 #include <sys/capability.h>
 #include <sys/cdefs.h>
 #include <sys/eventfd.h>
+#include <sys/mman.h>
 #include <sys/personality.h>
 #include <sys/prctl.h>
 #include <sys/resource.h>
@@ -69,6 +71,7 @@
 #include <android-base/properties.h>
 #include <android-base/file.h>
 #include <android-base/stringprintf.h>
+#include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 #include <cutils/fs.h>
 #include <cutils/multiuser.h>
@@ -1975,6 +1978,26 @@ static void com_android_internal_os_Zygote_nativeEmptyUsapPool(JNIEnv* env, jcla
   }
 }
 
+static int disable_execute_only(struct dl_phdr_info *info, size_t size, void *data) {
+  // Search for any execute-only segments and mark them read+execute.
+  for (int i = 0; i < info->dlpi_phnum; i++) {
+    if ((info->dlpi_phdr[i].p_type == PT_LOAD) && (info->dlpi_phdr[i].p_flags == PF_X)) {
+      mprotect(reinterpret_cast<void*>(info->dlpi_addr + info->dlpi_phdr[i].p_vaddr),
+              info->dlpi_phdr[i].p_memsz, PROT_READ | PROT_EXEC);
+    }
+  }
+  // Return non-zero to exit dl_iterate_phdr.
+  return 0;
+}
+
+/**
+ * @param env  Managed runtime environment
+ * @return  True if disable was successful.
+ */
+static jboolean com_android_internal_os_Zygote_nativeDisableExecuteOnly(JNIEnv* env, jclass) {
+  return dl_iterate_phdr(disable_execute_only, nullptr) == 0;
+}
+
 static const JNINativeMethod gMethods[] = {
     { "nativeSecurityInit", "()V",
       (void *) com_android_internal_os_Zygote_nativeSecurityInit },
@@ -2007,7 +2030,9 @@ static const JNINativeMethod gMethods[] = {
     { "nativeGetUsapPoolCount", "()I",
       (void *) com_android_internal_os_Zygote_nativeGetUsapPoolCount },
     { "nativeEmptyUsapPool", "()V",
-      (void *) com_android_internal_os_Zygote_nativeEmptyUsapPool }
+      (void *) com_android_internal_os_Zygote_nativeEmptyUsapPool },
+    { "nativeDisableExecuteOnly", "()Z",
+      (void *) com_android_internal_os_Zygote_nativeDisableExecuteOnly }
 };
 
 int register_com_android_internal_os_Zygote(JNIEnv* env) {