From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Thu, 10 Oct 2019 22:52:49 -0400
Subject: [PATCH] move pthread_internal_t behind guard page

Signed-off-by: anupritaisno1 <www.anuprita804@gmail.com>
---
 libc/bionic/pthread_create.cpp | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index 31c553e25..627fbb25b 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -201,10 +201,13 @@ int __init_thread(pthread_internal_t* thread) {
 ThreadMapping __allocate_thread_mapping(size_t stack_size, size_t stack_guard_size) {
   const StaticTlsLayout& layout = __libc_shared_globals()->static_tls_layout;
 
-  // Allocate in order: stack guard, stack, guard page, static TLS, guard page.
+  size_t thread_page_size = __BIONIC_ALIGN(sizeof(pthread_internal_t), PAGE_SIZE);
+
+  // Allocate in order: stack guard, stack, guard page, pthread_internal_t, static TLS, guard page.
   size_t mmap_size;
   if (__builtin_add_overflow(stack_size, stack_guard_size, &mmap_size)) return {};
   if (__builtin_add_overflow(mmap_size, PTHREAD_GUARD_SIZE, &mmap_size)) return {};
+  if (__builtin_add_overflow(mmap_size, thread_page_size, &mmap_size)) return {};
   if (__builtin_add_overflow(mmap_size, layout.size(), &mmap_size)) return {};
   if (__builtin_add_overflow(mmap_size, PTHREAD_GUARD_SIZE, &mmap_size)) return {};
 
@@ -233,9 +236,10 @@ ThreadMapping __allocate_thread_mapping(size_t stack_size, size_t stack_guard_si
     return {};
   }
 
-  char* const static_tls_space = space + stack_guard_size + stack_size + PTHREAD_GUARD_SIZE;
+  char* const thread = space + stack_guard_size + stack_size + PTHREAD_GUARD_SIZE;
+  char* const static_tls_space = thread + thread_page_size;
 
-  if (mprotect(static_tls_space, layout.size(), PROT_READ | PROT_WRITE) != 0) {
+  if (mprotect(thread, thread_page_size + layout.size(), PROT_READ | PROT_WRITE) != 0) {
     async_safe_format_log(ANDROID_LOG_WARN, "libc",
                           "pthread_create failed: couldn't mprotect R+W %zu-byte static TLS mapping region: %s",
                           layout.size(), strerror(errno));
@@ -280,13 +284,8 @@ static int __allocate_thread(pthread_attr_t* attr, bionic_tcb** tcbp, void** chi
     stack_top = static_cast<char*>(attr->stack_base) + attr->stack_size;
   }
 
-  // Carve out space from the stack for the thread's pthread_internal_t. This
-  // memory isn't counted in pthread_attr_getstacksize.
-
-  // To safely access the pthread_internal_t and thread stack, we need to find a 16-byte aligned boundary.
-  stack_top = align_down(stack_top - sizeof(pthread_internal_t), 16);
-
-  pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(stack_top);
+  pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(
+      mapping.static_tls - __BIONIC_ALIGN(sizeof(pthread_internal_t), PAGE_SIZE));
   if (!stack_clean) {
     // If thread was not allocated by mmap(), it may not have been cleared to zero.
     // So assume the worst and zero it.
