x64Emitter: Check end of allocated space when emitting code.

Source/Core/Common/Arm64Emitter.cpp

@@ -310,7 +310,7 @@ void ARM64XEmitter::SetCodePtrUnsafe(u8* ptr)
   m_code = ptr;
 }
 
-void ARM64XEmitter::SetCodePtr(u8* ptr)
+void ARM64XEmitter::SetCodePtr(u8* ptr, u8* end, bool write_failed)
 {
   SetCodePtrUnsafe(ptr);
   m_lastCacheFlushEnd = ptr;

Source/Core/Common/Arm64Emitter.h

@@ -540,7 +540,11 @@ public:
   }
 
   virtual ~ARM64XEmitter() {}
-  void SetCodePtr(u8* ptr);
+
+  // 'end' and 'write_failed' are unused in the ARM code emitter at the moment.
+  // They're just here for interface compatibility with the x64 code emitter.
+  void SetCodePtr(u8* ptr, u8* end, bool write_failed = false);
+
   void SetCodePtrUnsafe(u8* ptr);
   void ReserveCodeSpace(u32 bytes);
   u8* AlignCode16();

Source/Core/Common/CodeBlock.h

@@ -55,7 +55,7 @@ public:
     region_size = size;
     total_region_size = size;
     region = static_cast<u8*>(Common::AllocateExecutableMemory(total_region_size));
-    T::SetCodePtr(region);
+    T::SetCodePtr(region, region + size);
   }
 
   // Always clear code space with breakpoints, so that if someone accidentally executes
@@ -86,7 +86,7 @@ public:
   // Cannot currently be undone. Will write protect the entire code region.
   // Start over if you need to change the code (call FreeCodeSpace(), AllocCodeSpace()).
   void WriteProtect() { Common::WriteProtectMemory(region, region_size, true); }
-  void ResetCodePtr() { T::SetCodePtr(region); }
+  void ResetCodePtr() { T::SetCodePtr(region, region + region_size); }
   size_t GetSpaceLeft() const
   {
     ASSERT(static_cast<size_t>(T::GetCodePtr() - region) < region_size);

Source/Core/Common/x64Emitter.cpp

@@ -101,9 +101,11 @@ enum class FloatOp
   Invalid = -1,
 };
 
-void XEmitter::SetCodePtr(u8* ptr)
+void XEmitter::SetCodePtr(u8* ptr, u8* end, bool write_failed)
 {
   code = ptr;
+  m_code_end = end;
+  m_write_failed = write_failed;
 }
 
 const u8* XEmitter::GetCodePtr() const
@@ -116,31 +118,76 @@ u8* XEmitter::GetWritableCodePtr()
   return code;
 }
 
+const u8* XEmitter::GetCodeEnd() const
+{
+  return m_code_end;
+}
+
+u8* XEmitter::GetWritableCodeEnd()
+{
+  return m_code_end;
+}
+
 void XEmitter::Write8(u8 value)
 {
+  if (code >= m_code_end)
+  {
+    code = m_code_end;
+    m_write_failed = true;
+    return;
+  }
+
   *code++ = value;
 }
 
 void XEmitter::Write16(u16 value)
 {
+  if (code + sizeof(u16) > m_code_end)
+  {
+    code = m_code_end;
+    m_write_failed = true;
+    return;
+  }
+
   std::memcpy(code, &value, sizeof(u16));
   code += sizeof(u16);
 }
 
 void XEmitter::Write32(u32 value)
 {
+  if (code + sizeof(u32) > m_code_end)
+  {
+    code = m_code_end;
+    m_write_failed = true;
+    return;
+  }
+
   std::memcpy(code, &value, sizeof(u32));
   code += sizeof(u32);
 }
 
 void XEmitter::Write64(u64 value)
 {
+  if (code + sizeof(u64) > m_code_end)
+  {
+    code = m_code_end;
+    m_write_failed = true;
+    return;
+  }
+
   std::memcpy(code, &value, sizeof(u64));
   code += sizeof(u64);
 }
 
 void XEmitter::ReserveCodeSpace(int bytes)
 {
+  if (code + bytes > m_code_end)
+  {
+    code = m_code_end;
+    m_write_failed = true;
+    return;
+  }
+
   for (int i = 0; i < bytes; i++)
     *code++ = 0xCC;
 }
@@ -454,6 +501,13 @@ FixupBranch XEmitter::CALL()
   branch.ptr = code + 5;
   Write8(0xE8);
   Write32(0);
+
+  // If we couldn't write the full call instruction, indicate that in the returned FixupBranch by
+  // setting the branch's address to null. This will prevent a later SetJumpTarget() from writing to
+  // invalid memory.
+  if (HasWriteFailed())
+    branch.ptr = nullptr;
+
   return branch;
 }
 
@@ -473,6 +527,13 @@ FixupBranch XEmitter::J(bool force5bytes)
     Write8(0xE9);
     Write32(0);
   }
+
+  // If we couldn't write the full jump instruction, indicate that in the returned FixupBranch by
+  // setting the branch's address to null. This will prevent a later SetJumpTarget() from writing to
+  // invalid memory.
+  if (HasWriteFailed())
+    branch.ptr = nullptr;
+
   return branch;
 }
 
@@ -493,6 +554,13 @@ FixupBranch XEmitter::J_CC(CCFlags conditionCode, bool force5bytes)
     Write8(0x80 + conditionCode);
     Write32(0);
   }
+
+  // If we couldn't write the full jump instruction, indicate that in the returned FixupBranch by
+  // setting the branch's address to null. This will prevent a later SetJumpTarget() from writing to
+  // invalid memory.
+  if (HasWriteFailed())
+    branch.ptr = nullptr;
+
   return branch;
 }
 
@@ -518,6 +586,9 @@ void XEmitter::J_CC(CCFlags conditionCode, const u8* addr)
 
 void XEmitter::SetJumpTarget(const FixupBranch& branch)
 {
+  if (!branch.ptr)
+    return;
+
   if (branch.type == FixupBranch::Type::Branch8Bit)
   {
     s64 distance = (s64)(code - branch.ptr);

Source/Core/Common/x64Emitter.h

@@ -329,9 +329,19 @@ class XEmitter
 {
   friend struct OpArg;  // for Write8 etc
 private:
+  // Pointer to memory where code will be emitted to.
   u8* code = nullptr;
+
+  // Pointer past the end of the memory region we're allowed to emit to.
+  // Writes that would reach this memory are refused and will set the m_write_failed flag instead.
+  u8* m_code_end = nullptr;
+
   bool flags_locked = false;
 
+  // Set to true when a write request happens that would write past m_code_end.
+  // Must be cleared with SetCodePtr() afterwards.
+  bool m_write_failed = false;
+
   void CheckFlags();
 
   void Rex(int w, int r, int x, int b);
@@ -378,9 +388,9 @@ protected:
 
 public:
   XEmitter() = default;
-  explicit XEmitter(u8* code_ptr) : code{code_ptr} {}
+  explicit XEmitter(u8* code_ptr, u8* code_end) : code(code_ptr), m_code_end(code_end) {}
   virtual ~XEmitter() = default;
-  void SetCodePtr(u8* ptr);
+  void SetCodePtr(u8* ptr, u8* end, bool write_failed = false);
   void ReserveCodeSpace(int bytes);
   u8* AlignCodeTo(size_t alignment);
   u8* AlignCode4();
@@ -388,9 +398,16 @@ public:
   u8* AlignCodePage();
   const u8* GetCodePtr() const;
   u8* GetWritableCodePtr();
+  const u8* GetCodeEnd() const;
+  u8* GetWritableCodeEnd();
 
   void LockFlags() { flags_locked = true; }
   void UnlockFlags() { flags_locked = false; }
+
+  // Should be checked after a block of code has been generated to see if the code has been
+  // successfully written to memory. Do not call the generated code when this returns true!
+  bool HasWriteFailed() const { return m_write_failed; }
+
   // Looking for one of these? It's BANNED!! Some instructions are slow on modern CPU
   // INC, DEC, LOOP, LOOPNE, LOOPE, ENTER, LEAVE, XCHG, XLAT, REP MOVSB/MOVSD, REP SCASD + other
   // string instr.,