From 11d7bc52df55e487b78dce0fd70a88e5096987d9 Mon Sep 17 00:00:00 2001
From: Jiyong Park <jiyong@google.com>
Date: Fri, 15 Jul 2022 13:44:14 +0900
Subject: [PATCH] init: don't touch mmap_rnd_compat_bits on 64-bit only builds

mmap_rnd_compat_bits is for address space randomization of 32-bit
applications on 64-bit system. Configuring it is not only unnecessary
for 64-bit "only" builds, but also can cause a boot failure if the
kernel is built without CONFIG_COMPAT which is the case for Microdroid.

Use ro.product.abilist32 to determine whether 32-bit applications are
supported and if not, don't configure it, but mmap_rnd_bits.

Bug: 237950549
Test: run Microdroid with the kernel built with aosp/2153639

Change-Id: Ifca6fa02f14ad4c7d8f9b2ab8852494c12945c3a
---
 init/security.cpp | 5 +++--
 init/util.cpp     | 5 +++++
 init/util.h       | 1 +
 3 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/init/security.cpp b/init/security.cpp
index 970696e64..8bf4d5299 100644
--- a/init/security.cpp
+++ b/init/security.cpp
@@ -15,6 +15,7 @@
  */
 
 #include "security.h"
+#include "util.h"
 
 #include <errno.h>
 #include <fcntl.h>
@@ -106,12 +107,12 @@ Result<void> SetMmapRndBitsAction(const BuiltinArguments&) {
     return {};
 #elif defined(__aarch64__)
     // arm64 supports 18 - 33 bits depending on pagesize and VA_SIZE
-    if (SetMmapRndBitsMin(33, 24, false) && SetMmapRndBitsMin(16, 16, true)) {
+    if (SetMmapRndBitsMin(33, 24, false) && (!Has32BitAbi() || SetMmapRndBitsMin(16, 16, true))) {
         return {};
     }
 #elif defined(__x86_64__)
     // x86_64 supports 28 - 32 bits
-    if (SetMmapRndBitsMin(32, 32, false) && SetMmapRndBitsMin(16, 16, true)) {
+    if (SetMmapRndBitsMin(32, 32, false) && (!Has32BitAbi() || SetMmapRndBitsMin(16, 16, true))) {
         return {};
     }
 #elif defined(__arm__) || defined(__i386__)
diff --git a/init/util.cpp b/init/util.cpp
index 1801d1792..523cce451 100644
--- a/init/util.cpp
+++ b/init/util.cpp
@@ -733,5 +733,10 @@ bool IsMicrodroid() {
     return is_microdroid;
 }
 
+bool Has32BitAbi() {
+    static bool has = !android::base::GetProperty("ro.product.cpu.abilist32", "").empty();
+    return has;
+}
+
 }  // namespace init
 }  // namespace android
diff --git a/init/util.h b/init/util.h
index 47d4ff518..099b9eeae 100644
--- a/init/util.h
+++ b/init/util.h
@@ -106,5 +106,6 @@ bool IsDefaultMountNamespaceReady();
 void SetDefaultMountNamespaceReady();
 
 bool IsMicrodroid();
+bool Has32BitAbi();
 }  // namespace init
 }  // namespace android