[compiler-rt] Enhance function padding detection for function interception

[etienneb]

Summary

Many CRT (64-bits) functions contains a "hint-nop". The current padding
detection is not able to recognize the 10-bytes padding and the HotPatch
hooking technique cannot be used.

Other patterns may be discover and may be added later.

[etienneb]

nits

[rnk]

lgtm

lib/interception/interception_win.cc

 static bool IsMemoryPadding(uptr address, uptr size) {
   u8* function = (u8*)address;
   for (size_t i = 0; i < size; ++i)
     if (function[i] != 0x90 && function[i] != 0xCC)
       return false;
   return true;
 }
 
+static const u8 kHintNop10Bytes[] = {
+  0x66, 0x66, 0x0F, 0x1F, 0x84,
+  0x00, 0x00, 0x00, 0x00, 0x00
+};
+
+template<class T>
+NOINLINE static bool FunctionHasPrefix(uptr address, const T &pattern) {
+  u8* function = (u8*)address - sizeof(pattern);
+  for (size_t i = 0; i < sizeof(pattern); ++i)
+    if (function[i] != pattern[i])
+      return false;
+  return true;
+}
+
+NOINLINE static bool FunctionHasPadding(uptr address, uptr size) {
+  if (IsMemoryPadding(address - size, size))
+    return true;
+  if (size <= sizeof(kHintNop10Bytes) &&
+      FunctionHasPrefix(address, kHintNop10Bytes))
+    return true;
+  return false;
+}
+
 static void WritePadding(uptr from, uptr size) {
   _memset((void*)from, 0xCC, (size_t)size);
 }
 
 static void CopyInstructions(uptr from, uptr to, uptr size) {
   _memcpy((void*)from, (void*)to, (size_t)size);
 }
 
bool OverrideFunctionWithHotPatch(
   const int kHotPatchHeaderLen = kBranchLength;
 
   uptr header = (uptr)old_func - kHotPatchHeaderLen;
   uptr patch_length = kHotPatchHeaderLen + kShortJumpInstructionLength;
 
   // Validate that the function is hot patchable.
   size_t instruction_size = GetInstructionSize(old_func);
   if (instruction_size < kShortJumpInstructionLength ||
-      !IsMemoryPadding(header, kHotPatchHeaderLen))
+      !FunctionHasPadding(old_func, kHotPatchHeaderLen))
     return false;
 
   if (orig_old_func) {
     // Put the needed instructions into the trampoline bytes.
     uptr trampoline_length = instruction_size + kDirectBranchLength;
     uptr trampoline = AllocateMemoryForTrampoline(old_func, trampoline_length);
     if (!trampoline)
       return false;