1 files changed, 108 insertions, 0 deletions
diff --git a/mozglue/interposers/pthread_create_interposer.cpp b/mozglue/interposers/pthread_create_interposer.cpp
new file mode 100644
index 0000000000..65f60c2d1b
--- /dev/null
+++ b/mozglue/interposers/pthread_create_interposer.cpp
@@ -0,0 +1,108 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <algorithm>
+
+#include <pthread.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/DebugOnly.h"
+
+#include "InterposerHelper.h"
+
+using mozilla::DebugOnly;
+
+struct SigAltStack {
+  void* mem;
+  size_t size;
+};
+
+struct PthreadCreateParams {
+  void* (*start_routine)(void*);
+  void* arg;
+};
+
+// Install the alternate signal stack, returns a pointer to the memory area we
+// mapped to store the stack only if it was installed successfully, otherwise
+// returns NULL.
+static void* install_sig_alt_stack(size_t size) {
+  void* alt_stack_mem = mmap(nullptr, size, PROT_READ | PROT_WRITE,
+                             MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (alt_stack_mem) {
+    stack_t alt_stack = {
+        .ss_sp = alt_stack_mem,
+        .ss_flags = 0,
+        .ss_size = size,
+    };
+
+    int rv = sigaltstack(&alt_stack, nullptr);
+    if (rv == 0) {
+      return alt_stack_mem;
+    }
+
+    rv = munmap(alt_stack_mem, size);
+    MOZ_ASSERT(rv == 0);
+  }
+
+  return nullptr;
+}
+
+// Uninstall the alternate signal handler and unmaps it. Does nothing if
+// alt_stack_mem is NULL.
+static void uninstall_sig_alt_stack(void* alt_stack_ptr) {
+  SigAltStack* alt_stack = static_cast<SigAltStack*>(alt_stack_ptr);
+  if (alt_stack->mem) {
+    stack_t disable_alt_stack = {};
+    disable_alt_stack.ss_flags = SS_DISABLE;
+    DebugOnly<int> rv = sigaltstack(&disable_alt_stack, nullptr);
+    MOZ_ASSERT(rv == 0);
+    rv = munmap(alt_stack->mem, alt_stack->size);
+    MOZ_ASSERT(rv == 0);
+  }
+}
+
+// This replaces the routine passed to pthread_create() when a thread is
+// started, it handles the alternate signal stack and calls the thread's
+// actual routine.
+void* set_alt_signal_stack_and_start(PthreadCreateParams* params) {
+  void* (*start_routine)(void*) = params->start_routine;
+  void* arg = params->arg;
+  free(params);
+
+  void* thread_rv = nullptr;
+  static const size_t kSigStackSize = std::max(size_t(16384), size_t(SIGSTKSZ));
+  void* alt_stack_mem = install_sig_alt_stack(kSigStackSize);
+  SigAltStack alt_stack{alt_stack_mem, kSigStackSize};
+  pthread_cleanup_push(uninstall_sig_alt_stack, &alt_stack);
+  thread_rv = start_routine(arg);
+  pthread_cleanup_pop(1);
+
+  return thread_rv;
+}
+
+extern "C" {
+// This interposer replaces libpthread's pthread_create() so that we can
+// inject an alternate signal stack in every new thread.
+MFBT_API int pthread_create(pthread_t* thread, const pthread_attr_t* attr,
+                            void* (*start_routine)(void*), void* arg) {
+  static const auto real_pthread_create = GET_REAL_SYMBOL(pthread_create);
+
+  PthreadCreateParams* params =
+      (PthreadCreateParams*)malloc(sizeof(PthreadCreateParams));
+  params->start_routine = start_routine;
+  params->arg = arg;
+
+  int result = real_pthread_create(
+      thread, attr, (void* (*)(void*))set_alt_signal_stack_and_start, params);
+
+  if (result != 0) {
+    free(params);
+  }
+
+  return result;
+}
+}