From 2f6cd8dba8b7727abe37f8680dd6ad5a03b47158 Mon Sep 17 00:00:00 2001
From: Kamil Rytarowski <n54@gmx.com>
Date: Wed, 6 Dec 2017 21:57:39 +0000
Subject: Correct atexit(3) support in MSan/NetBSD

Summary:
The NetBSD specific implementation of cxa_atexit() does not
preserve the 2nd argument if dso is equal to NULL.

Changes:

 - Split paths of handling intercepted __cxa_atexit() and atexit(3).
   This affects all supported Operating Systems.
 - Add a local stack-like structure to hold the __cxa_atexit() context.
   atexit(3) is documented in the C standard as calling callback from the
   earliest to the oldest entry. This path also fixes potential ABI
   problem of passing an argument to a function from the atexit(3)
   callback mechanism.
 - Allow usage of global vars with ctors in interceptors.
   This allows to use Vector without automatic cleaning up the structures.

This code has been modeled after TSan implementation for the same functions.

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, dvyukov, eugenis, vitalybuka, kcc

Reviewed By: vitalybuka

Subscribers: llvm-commits, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D40714

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@319967 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/msan/msan_interceptors.cc | 66 +++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 63 insertions(+), 3 deletions(-)

(limited to 'lib')

diff --git a/lib/msan/msan_interceptors.cc b/lib/msan/msan_interceptors.cc
index ae9c89494..69c1aeb73 100644
--- a/lib/msan/msan_interceptors.cc
+++ b/lib/msan/msan_interceptors.cc
@@ -33,6 +33,7 @@
 #include "sanitizer_common/sanitizer_libc.h"
 #include "sanitizer_common/sanitizer_linux.h"
 #include "sanitizer_common/sanitizer_tls_get_addr.h"
+#include "sanitizer_common/sanitizer_vector.h"
 
 #if SANITIZER_NETBSD
 #define gettimeofday __gettimeofday50
@@ -1121,23 +1122,78 @@ struct MSanAtExitRecord {
   void *arg;
 };
 
-void MSanAtExitWrapper(void *arg) {
+struct InterceptorContext {
+  BlockingMutex atexit_mu;
+  Vector<struct MSanAtExitRecord *> AtExitStack;
+
+  InterceptorContext()
+      : AtExitStack() {
+  }
+};
+
+static ALIGNED(64) char interceptor_placeholder[sizeof(InterceptorContext)];
+InterceptorContext *interceptor_ctx() {
+  return reinterpret_cast<InterceptorContext*>(&interceptor_placeholder[0]);
+}
+
+void MSanAtExitWrapper() {
+  MSanAtExitRecord *r;
+  {
+    BlockingMutexLock l(&interceptor_ctx()->atexit_mu);
+
+    uptr element = interceptor_ctx()->AtExitStack.Size() - 1;
+    r = interceptor_ctx()->AtExitStack[element];
+    interceptor_ctx()->AtExitStack.PopBack();
+  }
+
+  UnpoisonParam(1);
+  ((void(*)())r->func)();
+  InternalFree(r);
+}
+
+void MSanCxaAtExitWrapper(void *arg) {
   UnpoisonParam(1);
   MSanAtExitRecord *r = (MSanAtExitRecord *)arg;
   r->func(r->arg);
   InternalFree(r);
 }
 
+static int setup_at_exit_wrapper(void(*f)(), void *arg, void *dso);
+
+// Unpoison argument shadow for C++ module destructors.
+INTERCEPTOR(int, atexit, void (*func)()) {
+  if (msan_init_is_running) return REAL(atexit)(func);
+  return setup_at_exit_wrapper((void(*)())func, 0, 0);
+}
+
 // Unpoison argument shadow for C++ module destructors.
 INTERCEPTOR(int, __cxa_atexit, void (*func)(void *), void *arg,
             void *dso_handle) {
   if (msan_init_is_running) return REAL(__cxa_atexit)(func, arg, dso_handle);
+  return setup_at_exit_wrapper((void(*)())func, arg, dso_handle);
+}
+
+static int setup_at_exit_wrapper(void(*f)(), void *arg, void *dso) {
   ENSURE_MSAN_INITED();
   MSanAtExitRecord *r =
       (MSanAtExitRecord *)InternalAlloc(sizeof(MSanAtExitRecord));
-  r->func = func;
+  r->func = (void(*)(void *a))f;
   r->arg = arg;
-  return REAL(__cxa_atexit)(MSanAtExitWrapper, r, dso_handle);
+  int res;
+  if (!dso) {
+    // NetBSD does not preserve the 2nd argument if dso is equal to 0
+    // Store ctx in a local stack-like structure
+
+    BlockingMutexLock l(&interceptor_ctx()->atexit_mu);
+
+    res = REAL(__cxa_atexit)((void (*)(void *a))MSanAtExitWrapper, 0, 0);
+    if (!res) {
+      interceptor_ctx()->AtExitStack.PushBack(r);
+    }
+  } else {
+    res = REAL(__cxa_atexit)(MSanCxaAtExitWrapper, r, dso);
+  }
+  return res;
 }
 
 static void BeforeFork() {
@@ -1535,6 +1591,9 @@ namespace __msan {
 void InitializeInterceptors() {
   static int inited = 0;
   CHECK_EQ(inited, 0);
+
+  new(interceptor_ctx()) InterceptorContext();
+
   InitializeCommonInterceptors();
   InitializeSignalInterceptors();
 
@@ -1650,6 +1709,7 @@ void InitializeInterceptors() {
 
   INTERCEPT_FUNCTION(pthread_join);
   INTERCEPT_FUNCTION(tzset);
+  INTERCEPT_FUNCTION(atexit);
   INTERCEPT_FUNCTION(__cxa_atexit);
   INTERCEPT_FUNCTION(shmat);
   INTERCEPT_FUNCTION(fork);
-- 
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