diff --git a/libs/binder/IPCThreadState.cpp b/libs/binder/IPCThreadState.cpp
index 8df83f1..14a801c 100644
--- a/libs/binder/IPCThreadState.cpp
+++ b/libs/binder/IPCThreadState.cpp
@@ -86,7 +86,8 @@
     "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;
@@ -440,12 +447,14 @@
 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();
 }
 
@@ -1122,10 +1131,19 @@
         }
         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;
@@ -1141,6 +1159,7 @@
                 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;
@@ -1153,10 +1172,12 @@
             clearPropagateWorkSource();
 
             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;
@@ -1188,8 +1209,8 @@
             }
 
             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);
@@ -1200,6 +1221,7 @@
             }
 
             mCallingPid = origPid;
+            mCallingSid = origSid;
             mCallingUid = origUid;
             mStrictModePolicy = origStrictModePolicy;
             mLastTransactionBinderFlags = origTransactionBinderFlags;