From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Sat, 1 Oct 2016 05:11:44 -0400
Subject: [PATCH] make __stack_chk_guard read-only at runtime

---
 libc/bionic/__libc_init_main_thread.cpp | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/libc/bionic/__libc_init_main_thread.cpp b/libc/bionic/__libc_init_main_thread.cpp
index 4984e38a1..2e3967daa 100644
--- a/libc/bionic/__libc_init_main_thread.cpp
+++ b/libc/bionic/__libc_init_main_thread.cpp
@@ -28,6 +28,9 @@
 
 #include "libc_init_common.h"
 
+#include <limits.h>
+#include <sys/mman.h>
+
 #include <async_safe/log.h>
 
 #include "private/KernelArgumentBlock.h"
@@ -35,17 +38,20 @@
 #include "private/bionic_defs.h"
 #include "private/bionic_elf_tls.h"
 #include "private/bionic_globals.h"
-#include "private/bionic_ssp.h"
 #include "pthread_internal.h"
 
 extern "C" pid_t __getpid();
 extern "C" int __set_tid_address(int* tid_address);
 
 // Declared in "private/bionic_ssp.h".
-uintptr_t __stack_chk_guard = 0;
+__attribute__((aligned(PAGE_SIZE)))
+uintptr_t __stack_chk_guard[PAGE_SIZE / sizeof(uintptr_t)] = {0};
 
 static pthread_internal_t main_thread;
 
+void __libc_init_global_stack_chk_guard(KernelArgumentBlock& args) {
+}
+
 // Setup for the main thread. For dynamic executables, this is called by the
 // linker _before_ libc is mapped in memory. This means that all writes to
 // globals from this function will apply to linker-private copies and will not
@@ -101,7 +107,10 @@ extern "C" void __libc_init_main_thread_late() {
   // The TLS stack guard is set from the global, so ensure that we've initialized the global
   // before we initialize the TLS. Dynamic executables will initialize their copy of the global
   // stack protector from the one in the main thread's TLS.
-  __libc_safe_arc4random_buf(&__stack_chk_guard, sizeof(__stack_chk_guard));
+  __libc_safe_arc4random_buf(&__stack_chk_guard[0], sizeof(__stack_chk_guard[0]));
+  if (mprotect(__stack_chk_guard, sizeof(__stack_chk_guard), PROT_READ) == -1) {
+    async_safe_fatal("mprotect __stack_chk_guard: %s", strerror(errno));
+  }
   __init_tcb_stack_guard(__get_bionic_tcb());
 
   __init_thread(&main_thread);
