wasm2c: Add macro and tests to allow disabling stack exhaustion checks

Author: shravanrn

.github/workflows/build.yml

@@ -172,7 +172,7 @@ jobs:
     runs-on: ubuntu-latest
     env:
       USE_NINJA: "1"
-      WASM2C_CFLAGS: "-DWASM_RT_USE_MMAP=1 -DWASM_RT_SKIP_SIGNAL_RECOVERY=1 -DWASM2C_TEST_EMBEDDER_SIGNAL_HANDLING"
+      WASM2C_CFLAGS: "-DWASM_RT_USE_MMAP=1 -DWASM_RT_SKIP_SIGNAL_RECOVERY=1 -DWASM_RT_NONCONFORMING_STACK_UNCHECKED=1 -DWASM2C_TEST_EMBEDDER_SIGNAL_HANDLING"
     steps:
     - uses: actions/setup-python@v1
       with:
@@ -182,5 +182,5 @@ jobs:
         submodules: true
     - run: sudo apt-get install ninja-build
     - run: make clang-debug
-    - name: tests (excluding memory64)
-      run: ./test/run-tests.py --exclude-dir memory64
+    - name: tests (wasm2c tests excluding memory64 and stack exhaustion)
+      run: ./test/run-tests.py *wasm2c* --exclude memory64 --exclude call.txt --exclude call_indirect.txt --exclude fac.txt --exclude skip-stack-guard-page.txt

test/run-tests.py

@@ -684,17 +684,18 @@ def _Clear(self):
         sys.stderr.write('\r%s\r' % (' ' * self.last_length))
 
 
-def FindTestFiles(ext, filter_pattern_re, exclude_dirs):
+def FindTestFiles(ext, filter_pattern_re, excludes):
     tests = []
     for root, dirs, files in os.walk(TEST_DIR):
-        for ex in exclude_dirs:
+        for ex in excludes:
             if ex in dirs:
                 # Filtering out dirs here causes os.walk not to descend into them
                 dirs.remove(ex)
         for f in files:
-            path = os.path.join(root, f)
-            if os.path.splitext(f)[1] == ext:
-                tests.append(os.path.relpath(path, REPO_ROOT_DIR))
+            if f not in excludes:
+                path = os.path.join(root, f)
+                if os.path.splitext(f)[1] == ext:
+                    tests.append(os.path.relpath(path, REPO_ROOT_DIR))
     tests.sort()
     return [test for test in tests if re.match(filter_pattern_re, test)]
 
@@ -928,10 +929,10 @@ def main(args):
                         action='store_true')
     parser.add_argument('patterns', metavar='pattern', nargs='*',
                         help='test patterns.')
-    parser.add_argument('--exclude-dir', action='append', default=[],
-                        help='directory to exclude.')
+    parser.add_argument('--exclude', action='append', default=[],
+                        help='file or directory names to exclude.')
     options = parser.parse_args(args)
-    exclude_dirs = options.exclude_dir
+    excludes = options.exclude
 
     if options.jobs != 1:
         if options.fail_fast:
@@ -947,9 +948,9 @@ def main(args):
         # By default, exclude wasi tests because WASI support is not include
         # by int the build by default.
         # TODO(sbc): Find some way to detect the WASI support.
-        exclude_dirs += ['wasi']
+        excludes += ['wasi']
 
-    test_names = FindTestFiles('.txt', pattern_re, exclude_dirs)
+    test_names = FindTestFiles('.txt', pattern_re, excludes)
 
     if options.list:
         for test_name in test_names:

test/spec-wasm2c-prefix.c

@@ -373,6 +373,7 @@ static void posix_signal_handler(int sig, siginfo_t* si, void* unused) {
 }
 
 static void posix_install_signal_handler(void) {
+#if !WASM_RT_NONCONFORMING_STACK_UNCHECKED
   /* install altstack */
   stack_t ss;
   ss.ss_sp = malloc(SIGSTKSZ);
@@ -382,11 +383,15 @@ static void posix_install_signal_handler(void) {
     perror("sigaltstack failed");
     abort();
   }
+#endif
 
   /* install signal handler */
   struct sigaction sa;
   memset(&sa, '\0', sizeof(sa));
-  sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
+  sa.sa_flags = SA_SIGINFO;
+#if !WASM_RT_NONCONFORMING_STACK_UNCHECKED
+  sa.sa_flags |= SA_ONSTACK;
+#endif
   sigemptyset(&sa.sa_mask);
   sa.sa_sigaction = posix_signal_handler;
   if (sigaction(SIGSEGV, &sa, NULL) != 0 || sigaction(SIGBUS, &sa, NULL) != 0) {
@@ -405,6 +410,7 @@ static void posix_cleanup_signal_handler(void) {
     abort();
   }
 
+#if !WASM_RT_NONCONFORMING_STACK_UNCHECKED
   /* disable and free altstack */
   stack_t ss;
   ss.ss_flags = SS_DISABLE;
@@ -413,6 +419,7 @@ static void posix_cleanup_signal_handler(void) {
     abort();
   }
   free(ss.ss_sp);
+#endif
 }
 #endif
 

wasm2c/wasm-rt.h

@@ -166,11 +166,20 @@ extern "C" {
 #define WASM_RT_INSTALL_SIGNAL_HANDLER 0
 #endif
 
+/* This macro, if defined, allows the embedder to disable all stack exhaustion
+ * checks. This a non conformant configuration, i.e., this does not respect
+ * Wasm's specification, and may compromise security. Use with caution.
+ */
+#ifndef WASM_RT_NONCONFORMING_STACK_UNCHECKED
+#define WASM_RT_NONCONFORMING_STACK_UNCHECKED 0
+#endif
+
 /* We need to detect and trap stack overflows. If we use a signal handler on
  * POSIX systems, this can detect call stack overflows. On windows, or platforms
  * without a signal handler, we use stack depth counting. */
-#if !defined(WASM_RT_STACK_DEPTH_COUNT) && \
-    !defined(WASM_RT_STACK_EXHAUSTION_HANDLER)
+#if !defined(WASM_RT_STACK_DEPTH_COUNT) &&        \
+    !defined(WASM_RT_STACK_EXHAUSTION_HANDLER) && \
+    !WASM_RT_NONCONFORMING_STACK_UNCHECKED
 
 #if WASM_RT_INSTALL_SIGNAL_HANDLER && !defined(_WIN32)
 #define WASM_RT_STACK_EXHAUSTION_HANDLER 1
@@ -188,6 +197,15 @@ extern "C" {
 #define WASM_RT_STACK_EXHAUSTION_HANDLER 0
 #endif
 
+#if WASM_RT_NONCONFORMING_STACK_UNCHECKED
+
+#if (WASM_RT_STACK_EXHAUSTION_HANDLER + WASM_RT_STACK_DEPTH_COUNT) != 0
+#error \
+    "Cannot specify WASM_RT_NONCONFORMING_STACK_UNCHECKED along with WASM_RT_STACK_EXHAUSTION_HANDLER or WASM_RT_STACK_DEPTH_COUNT"
+#endif
+
+#else
+
 #if (WASM_RT_STACK_EXHAUSTION_HANDLER + WASM_RT_STACK_DEPTH_COUNT) > 1
 #error \
     "Cannot specify multiple options from WASM_RT_STACK_EXHAUSTION_HANDLER , WASM_RT_STACK_DEPTH_COUNT"
@@ -196,6 +214,8 @@ extern "C" {
     "Must specify one of WASM_RT_STACK_EXHAUSTION_HANDLER , WASM_RT_STACK_DEPTH_COUNT"
 #endif
 
+#endif
+
 #if WASM_RT_STACK_EXHAUSTION_HANDLER && !WASM_RT_INSTALL_SIGNAL_HANDLER
 #error \
     "WASM_RT_STACK_EXHAUSTION_HANDLER  can only be used if WASM_RT_INSTALL_SIGNAL_HANDLER is enabled"