Add an API for per-process disabling memory initialization.
Introduce an android_mallopt(M_DISABLE_MEMORY_MITIGATIONS) API call
that may be used to disable zero- or pattern-init on non-MTE hardware,
or memory tagging on MTE hardware. The intent is that this function
may be called at any time, including when there are multiple threads
running.
Disabling zero- or pattern-init is quite trivial, we just need to set
a global variable to 0 via a Scudo API call (although there will be
some separate work required on the Scudo side to make this operation
thread-safe).
It is a bit more tricky to disable MTE across a process, because
the kernel does not provide an API for disabling tag checking in all
threads in a process, only per-thread. We need to send a signal to each
of the process's threads with a handler that issues the required prctl
call, and lock thread creation for the duration of the API call to
avoid races between thread enumeration and calls to pthread_create().
Bug: 135772972
Change-Id: I81ece86ace916eb6b435ab516cd431ec4b48a3bf
diff --git a/libc/bionic/memory_mitigation_state.cpp b/libc/bionic/memory_mitigation_state.cpp
new file mode 100644
index 0000000..82b0b7b
--- /dev/null
+++ b/libc/bionic/memory_mitigation_state.cpp
@@ -0,0 +1,86 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "memory_mitigation_state.h"
+
+#include <dirent.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <stdatomic.h>
+#include <stdlib.h>
+#include <sys/prctl.h>
+#include <sys/types.h>
+
+#include <bionic/mte.h>
+#include <bionic/reserved_signals.h>
+
+#include "private/ScopedRWLock.h"
+#include "pthread_internal.h"
+
+extern "C" void scudo_malloc_set_zero_contents(int zero_contents);
+extern "C" void scudo_malloc_disable_memory_tagging();
+
+#ifdef ANDROID_EXPERIMENTAL_MTE
+static bool set_tcf_on_all_threads(int tcf) {
+ static int g_tcf;
+ g_tcf = tcf;
+
+ return android_run_on_all_threads(
+ [](void*) {
+ int tagged_addr_ctrl = prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0);
+ if (tagged_addr_ctrl < 0) {
+ return false;
+ }
+
+ tagged_addr_ctrl = (tagged_addr_ctrl & ~PR_MTE_TCF_MASK) | g_tcf;
+ if (prctl(PR_SET_TAGGED_ADDR_CTRL, tagged_addr_ctrl, 0, 0, 0) < 0) {
+ return false;
+ }
+ return true;
+ },
+ nullptr);
+}
+#endif
+
+bool DisableMemoryMitigations(void* arg, size_t arg_size) {
+ if (arg || arg_size) {
+ return false;
+ }
+
+#ifdef USE_SCUDO
+ scudo_malloc_set_zero_contents(0);
+
+#ifdef ANDROID_EXPERIMENTAL_MTE
+ if (mte_supported() && set_tcf_on_all_threads(PR_MTE_TCF_NONE)) {
+ scudo_malloc_disable_memory_tagging();
+ }
+#endif
+#endif
+
+ return true;
+}