diff --git a/libs/binder/Binder.cpp b/libs/binder/Binder.cpp
index f6cc3af..96ee295 100644
--- a/libs/binder/Binder.cpp
+++ b/libs/binder/Binder.cpp
@@ -86,6 +86,10 @@
 class BBinder::Extras
 {
 public:
+    // unlocked objects
+    bool mRequestingSid = false;
+
+    // for below objects
     Mutex mLock;
     BpBinder::ObjectManager mObjects;
 };
@@ -163,19 +167,8 @@
     const void* objectID, void* object, void* cleanupCookie,
     object_cleanup_func func)
 {
-    Extras* e = mExtras.load(std::memory_order_acquire);
-
-    if (!e) {
-        e = new Extras;
-        Extras* expected = nullptr;
-        if (!mExtras.compare_exchange_strong(expected, e,
-                                             std::memory_order_release,
-                                             std::memory_order_acquire)) {
-            delete e;
-            e = expected;  // Filled in by CAS
-        }
-        if (e == nullptr) return; // out of memory
-    }
+    Extras* e = getOrCreateExtras();
+    if (!e) return; // out of memory
 
     AutoMutex _l(e->mLock);
     e->mObjects.attach(objectID, object, cleanupCookie, func);
@@ -204,6 +197,30 @@
     return this;
 }
 
+bool BBinder::isRequestingSid()
+{
+    Extras* e = mExtras.load(std::memory_order_acquire);
+
+    return e && e->mRequestingSid;
+}
+
+void BBinder::setRequestingSid(bool requestingSid)
+{
+    Extras* e = mExtras.load(std::memory_order_acquire);
+
+    if (!e) {
+        // default is false. Most things don't need sids, so avoiding allocations when possible.
+        if (!requestingSid) {
+            return;
+        }
+
+        e = getOrCreateExtras();
+        if (!e) return; // out of memory
+    }
+
+    e->mRequestingSid = true;
+}
+
 BBinder::~BBinder()
 {
     Extras* e = mExtras.load(std::memory_order_relaxed);
@@ -267,6 +284,25 @@
     }
 }
 
+BBinder::Extras* BBinder::getOrCreateExtras()
+{
+    Extras* e = mExtras.load(std::memory_order_acquire);
+
+    if (!e) {
+        e = new Extras;
+        Extras* expected = nullptr;
+        if (!mExtras.compare_exchange_strong(expected, e,
+                                             std::memory_order_release,
+                                             std::memory_order_acquire)) {
+            delete e;
+            e = expected;  // Filled in by CAS
+        }
+        if (e == nullptr) return nullptr; // out of memory
+    }
+
+    return e;
+}
+
 // ---------------------------------------------------------------------------
 
 enum {
diff --git a/libs/binder/IPCThreadState.cpp b/libs/binder/IPCThreadState.cpp
index 22f6f54..e60f03a 100644
--- a/libs/binder/IPCThreadState.cpp
+++ b/libs/binder/IPCThreadState.cpp
@@ -88,7 +88,8 @@
     "BR_FINISHED",
     "BR_DEAD_BINDER",
     "BR_CLEAR_DEATH_NOTIFICATION_DONE",
-    "BR_FAILED_REPLY"
+    "BR_FAILED_REPLY",
+    "BR_TRANSACTION_SEC_CTX",
 };
 
 static const char *kCommandStrings[] = {
@@ -363,6 +364,11 @@
     return mCallingPid;
 }
 
+const char* IPCThreadState::getCallingSid() const
+{
+    return mCallingSid;
+}
+
 uid_t IPCThreadState::getCallingUid() const
 {
     return mCallingUid;
@@ -370,6 +376,7 @@
 
 int64_t IPCThreadState::clearCallingIdentity()
 {
+    // ignore mCallingSid for legacy reasons
     int64_t token = ((int64_t)mCallingUid<<32) | mCallingPid;
     clearCaller();
     return token;
@@ -398,12 +405,14 @@
 void IPCThreadState::restoreCallingIdentity(int64_t token)
 {
     mCallingUid = (int)(token>>32);
+    mCallingSid = nullptr;  // not enough data to restore
     mCallingPid = (int)token;
 }
 
 void IPCThreadState::clearCaller()
 {
     mCallingPid = getpid();
+    mCallingSid = nullptr;  // expensive to lookup
     mCallingUid = getuid();
 }
 
@@ -1089,10 +1098,19 @@
         }
         break;
 
+    case BR_TRANSACTION_SEC_CTX:
     case BR_TRANSACTION:
         {
-            binder_transaction_data tr;
-            result = mIn.read(&tr, sizeof(tr));
+            binder_transaction_data_secctx tr_secctx;
+            binder_transaction_data& tr = tr_secctx.transaction_data;
+
+            if (cmd == (int) BR_TRANSACTION_SEC_CTX) {
+                result = mIn.read(&tr_secctx, sizeof(tr_secctx));
+            } else {
+                result = mIn.read(&tr, sizeof(tr));
+                tr_secctx.secctx = 0;
+            }
+
             ALOG_ASSERT(result == NO_ERROR,
                 "Not enough command data for brTRANSACTION");
             if (result != NO_ERROR) break;
@@ -1108,15 +1126,18 @@
                 tr.offsets_size/sizeof(binder_size_t), freeBuffer, this);
 
             const pid_t origPid = mCallingPid;
+            const char* origSid = mCallingSid;
             const uid_t origUid = mCallingUid;
             const int32_t origStrictModePolicy = mStrictModePolicy;
             const int32_t origTransactionBinderFlags = mLastTransactionBinderFlags;
 
             mCallingPid = tr.sender_pid;
+            mCallingSid = reinterpret_cast<const char*>(tr_secctx.secctx);
             mCallingUid = tr.sender_euid;
             mLastTransactionBinderFlags = tr.flags;
 
-            //ALOGI(">>>> TRANSACT from pid %d uid %d\n", mCallingPid, mCallingUid);
+            // ALOGI(">>>> TRANSACT from pid %d sid %s uid %d\n", mCallingPid,
+            //    (mCallingSid ? mCallingSid : "<N/A>"), mCallingUid);
 
             Parcel reply;
             status_t error;
@@ -1148,8 +1169,8 @@
             }
 
             mIPCThreadStateBase->popCurrentState();
-            //ALOGI("<<<< TRANSACT from pid %d restore pid %d uid %d\n",
-            //     mCallingPid, origPid, origUid);
+            //ALOGI("<<<< TRANSACT from pid %d restore pid %d sid %s uid %d\n",
+            //     mCallingPid, origPid, (origSid ? origSid : "<N/A>"), origUid);
 
             if ((tr.flags & TF_ONE_WAY) == 0) {
                 LOG_ONEWAY("Sending reply to %d!", mCallingPid);
@@ -1160,6 +1181,7 @@
             }
 
             mCallingPid = origPid;
+            mCallingSid = origSid;
             mCallingUid = origUid;
             mStrictModePolicy = origStrictModePolicy;
             mLastTransactionBinderFlags = origTransactionBinderFlags;
diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index ca6a97d..9f8c408 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -215,7 +215,7 @@
     }
 
     if (binder != nullptr) {
-        IBinder *local = binder->localBinder();
+        BBinder *local = binder->localBinder();
         if (!local) {
             BpBinder *proxy = binder->remoteBinder();
             if (proxy == nullptr) {
@@ -227,6 +227,9 @@
             obj.handle = handle;
             obj.cookie = 0;
         } else {
+            if (local->isRequestingSid()) {
+                obj.flags |= FLAT_BINDER_FLAG_TXN_SECURITY_CTX;
+            }
             obj.hdr.type = BINDER_TYPE_BINDER;
             obj.binder = reinterpret_cast<uintptr_t>(local->getWeakRefs());
             obj.cookie = reinterpret_cast<uintptr_t>(local);
diff --git a/libs/binder/ProcessState.cpp b/libs/binder/ProcessState.cpp
index 3798b61..79db0cb 100644
--- a/libs/binder/ProcessState.cpp
+++ b/libs/binder/ProcessState.cpp
@@ -181,8 +181,20 @@
         mBinderContextCheckFunc = checkFunc;
         mBinderContextUserData = userData;
 
-        int dummy = 0;
-        status_t result = ioctl(mDriverFD, BINDER_SET_CONTEXT_MGR, &dummy);
+        flat_binder_object obj {
+            .flags = FLAT_BINDER_FLAG_TXN_SECURITY_CTX,
+        };
+
+        status_t result = ioctl(mDriverFD, BINDER_SET_CONTEXT_MGR_EXT, &obj);
+
+        // fallback to original method
+        if (result != 0) {
+            android_errorWriteLog(0x534e4554, "121035042");
+
+            int dummy = 0;
+            result = ioctl(mDriverFD, BINDER_SET_CONTEXT_MGR, &dummy);
+        }
+
         if (result == 0) {
             mManagesContexts = true;
         } else if (result == -1) {
diff --git a/libs/binder/include/binder/Binder.h b/libs/binder/include/binder/Binder.h
index c251468..cf3ef84 100644
--- a/libs/binder/include/binder/Binder.h
+++ b/libs/binder/include/binder/Binder.h
@@ -60,6 +60,10 @@
 
     virtual BBinder*    localBinder();
 
+    bool                isRequestingSid();
+    // This must be called before the object is sent to another process. Not thread safe.
+    void                setRequestingSid(bool requestSid);
+
 protected:
     virtual             ~BBinder();
 
@@ -75,6 +79,8 @@
 
     class Extras;
 
+    Extras*             getOrCreateExtras();
+
     std::atomic<Extras*> mExtras;
             void*       mReserved0;
 };
diff --git a/libs/binder/include/binder/IPCThreadState.h b/libs/binder/include/binder/IPCThreadState.h
index 745f618..a20ef7c 100644
--- a/libs/binder/include/binder/IPCThreadState.h
+++ b/libs/binder/include/binder/IPCThreadState.h
@@ -42,6 +42,11 @@
             status_t            clearLastError();
 
             pid_t               getCallingPid() const;
+            // nullptr if unavailable
+            //
+            // this can't be restored once it's cleared, and it does not return the
+            // context of the current process when not in a binder call.
+            const char*         getCallingSid() const;
             uid_t               getCallingUid() const;
 
             void                setStrictModePolicy(int32_t policy);
@@ -51,6 +56,7 @@
             int32_t             getLastTransactionBinderFlags() const;
 
             int64_t             clearCallingIdentity();
+            // Restores PID/UID (not SID)
             void                restoreCallingIdentity(int64_t token);
             
             int                 setupPolling(int* fd);
@@ -154,6 +160,7 @@
             Parcel              mOut;
             status_t            mLastError;
             pid_t               mCallingPid;
+            const char*         mCallingSid;
             uid_t               mCallingUid;
             int32_t             mStrictModePolicy;
             int32_t             mLastTransactionBinderFlags;
diff --git a/libs/binder/include/binder/Parcel.h b/libs/binder/include/binder/Parcel.h
index c9c273a..8db50e7 100644
--- a/libs/binder/include/binder/Parcel.h
+++ b/libs/binder/include/binder/Parcel.h
@@ -27,8 +27,8 @@
 #include <utils/String16.h>
 #include <utils/Vector.h>
 #include <utils/Flattenable.h>
-#include <linux/android/binder.h>
 
+#include <binder/binder_kernel.h>
 #include <binder/IInterface.h>
 #include <binder/Parcelable.h>
 #include <binder/Map.h>
diff --git a/libs/binder/include/binder/binder_kernel.h b/libs/binder/include/binder/binder_kernel.h
new file mode 100644
index 0000000..c7f6b4b
--- /dev/null
+++ b/libs/binder/include/binder/binder_kernel.h
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_BINDER_KERNEL_H
+#define ANDROID_BINDER_KERNEL_H
+
+#include <linux/android/binder.h>
+
+/**
+ * This file exists because the uapi kernel headers in bionic are built
+ * from upstream kernel headers only, and not all of the hwbinder kernel changes
+ * have made it upstream yet. Therefore, the modifications to the
+ * binder header are added locally in this file.
+ */
+
+enum {
+        FLAT_BINDER_FLAG_TXN_SECURITY_CTX = 0x1000,
+};
+
+#define BINDER_SET_CONTEXT_MGR_EXT      _IOW('b', 13, struct flat_binder_object)
+
+struct binder_transaction_data_secctx {
+        struct binder_transaction_data transaction_data;
+        binder_uintptr_t secctx;
+};
+
+enum {
+        BR_TRANSACTION_SEC_CTX = _IOR('r', 2,
+                              struct binder_transaction_data_secctx),
+};
+
+#endif // ANDROID_BINDER_KERNEL_H