From 868e1ee1d02c153d867a9f4e2b7e35df7d0701df Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka@google.com>
Date: Tue, 19 Jul 2022 21:17:06 -0700
Subject: [PATCH] Revert "[libasan] Remove 4Mb stack limit for swapcontext
 unpoisoning"

This patches exposed existing incorectness of swapcontext imlementation.
swapcontext does not set oucp->uc_stack. Unpoisoning works if ucp is
from makecontext, but may try to use garbage pointers if it's from
previos swapcontext or from getcontext. Existing limit reduces
probability of garbage pointers are used.

I restore behavour which we had for years, and will look to improve
swapcontext support.

This reverts commit d0751c9725aab1dad3d86481e13a4628356e7422.
---
 compiler-rt/lib/asan/asan_interceptors.cpp    |  3 +-
 .../Linux/swapcontext_annotation.cpp          | 53 +------------------
 2 files changed, 3 insertions(+), 53 deletions(-)

diff --git a/compiler-rt/lib/asan/asan_interceptors.cpp b/compiler-rt/lib/asan/asan_interceptors.cpp
index 13311b7e409b..6c843968f7af 100644
--- a/compiler-rt/lib/asan/asan_interceptors.cpp
+++ b/compiler-rt/lib/asan/asan_interceptors.cpp
@@ -248,7 +248,8 @@ static void ClearShadowMemoryForContextStack(uptr stack, uptr ssize) {
   uptr bottom = stack & ~(PageSize - 1);
   ssize += stack - bottom;
   ssize = RoundUpTo(ssize, PageSize);
-  if (AddrIsInMem(bottom) && ssize)
+  static const uptr kMaxSaneContextStackSize = 1 << 22;  // 4 Mb
+  if (AddrIsInMem(bottom) && ssize && ssize <= kMaxSaneContextStackSize)
     PoisonShadow(bottom, ssize, 0);
 }
 
diff --git a/compiler-rt/test/asan/TestCases/Linux/swapcontext_annotation.cpp b/compiler-rt/test/asan/TestCases/Linux/swapcontext_annotation.cpp
index 5753f1397963..fd5ae17c4d0a 100644
--- a/compiler-rt/test/asan/TestCases/Linux/swapcontext_annotation.cpp
+++ b/compiler-rt/test/asan/TestCases/Linux/swapcontext_annotation.cpp
@@ -146,61 +146,9 @@ int Run(int arg, int mode, char *child_stack) {
   return child_stack[arg];
 }
 
-ucontext_t orig_huge_stack_context;
-ucontext_t child_huge_stack_context;
-
-// There used to be a limitation for stack unpoisoning (size <= 4Mb), check that it's gone.
-const int kHugeStackSize = 1 << 23;
-
-void ChildHugeStack() {
-  __sanitizer_finish_switch_fiber(nullptr, &main_thread_stack,
-                                  &main_thread_stacksize);
-  char x[32] = {0}; // Stack gets poisoned.
-  __sanitizer_start_switch_fiber(nullptr, main_thread_stack,
-                                 main_thread_stacksize);
-  if (swapcontext(&child_huge_stack_context, &orig_huge_stack_context) < 0) {
-    perror("swapcontext");
-    _exit(1);
-  }
-}
-
-void DoRunHugeStack(char *child_stack) {
-  getcontext(&child_huge_stack_context);
-  child_huge_stack_context.uc_stack.ss_sp = child_stack;
-  child_huge_stack_context.uc_stack.ss_size = kHugeStackSize;
-  makecontext(&child_huge_stack_context, (void (*)())ChildHugeStack, 0);
-  void *fake_stack_save;
-  __sanitizer_start_switch_fiber(&fake_stack_save,
-                                 child_huge_stack_context.uc_stack.ss_sp,
-                                 child_huge_stack_context.uc_stack.ss_size);
-  if (swapcontext(&orig_huge_stack_context, &child_huge_stack_context) < 0) {
-    perror("swapcontext");
-    _exit(1);
-  }
-  __sanitizer_finish_switch_fiber(
-      fake_stack_save, (const void **)&child_huge_stack_context.uc_stack.ss_sp,
-      &child_huge_stack_context.uc_stack.ss_size);
-  for (int i = 0; i < kHugeStackSize; ++i) {
-    child_stack[i] = i;
-  }
-}
-
-void RunHugeStack() {
-  const int run_offset = 1 << 14;
-  char *heap = new char[kHugeStackSize + run_offset + 1];
-  DoRunHugeStack(heap);
-  DoRunHugeStack(heap + run_offset);
-  DoRunHugeStack(heap);
-  delete[] heap;
-}
-
 void handler(int sig) { CallNoReturn(); }
 
 int main(int argc, char **argv) {
-  // CHECK: WARNING: ASan doesn't fully support makecontext/swapcontext
-  // CHECK-NOT: ASan is ignoring requested __asan_handle_no_return
-  RunHugeStack();
-
   // set up a signal that will spam and trigger __asan_handle_no_return at
   // tricky moments
   struct sigaction act = {};
@@ -222,6 +170,7 @@ int main(int argc, char **argv) {
   char *heap = new char[kStackSize + 1];
   next_child_stack = new char[kStackSize + 1];
   char stack[kStackSize + 1];
+  // CHECK: WARNING: ASan doesn't fully support makecontext/swapcontext
   int ret = 0;
   // CHECK-NOT: ASan is ignoring requested __asan_handle_no_return
   for (unsigned int i = 0; i < 30; ++i) {