Allow ASLR to be disabled on Windows

On Windows, it is possible to disable ASLR when creating a process.
This patch adds code to do this, and hooks it up to gdb's existing
disable-randomization feature.  Because the Windows documentation
cautions that this isn't available on all versions of Windows, the
CreateProcess wrapper function is updated to make the attempt, and
then fall back to the current approach if it fails.

6 files changed, 164 insertions, 4 deletions

diff --git a/gdb/NEWS b/gdb/NEWS
index a85f59f56df..7164e18bfa5 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -71,6 +71,8 @@ maintenance info line-table
   Python 2.  From GDB 13, it will only be possible to build GDB itself
   with Python 3 support.
 
+* The disable-randomization setting now works on Windows.
+
 * Improved C++ template support
 
   GDB now treats functions/types involving C++ templates like it does function
diff --git a/gdb/nat/windows-nat.c b/gdb/nat/windows-nat.c
index 8048344752b..e52da16d9ce 100644
--- a/gdb/nat/windows-nat.c
+++ b/gdb/nat/windows-nat.c
@@ -69,6 +69,10 @@ GenerateConsoleCtrlEvent_ftype *GenerateConsoleCtrlEvent;
 typedef HRESULT WINAPI (GetThreadDescription_ftype) (HANDLE, PWSTR *);
 static GetThreadDescription_ftype *GetThreadDescription;
 
+InitializeProcThreadAttributeList_ftype *InitializeProcThreadAttributeList;
+UpdateProcThreadAttribute_ftype *UpdateProcThreadAttribute;
+DeleteProcThreadAttributeList_ftype *DeleteProcThreadAttributeList;
+
 /* Note that 'debug_events' must be locally defined in the relevant
    functions.  */
 #define DEBUG_EVENTS(fmt, ...) \
@@ -741,15 +745,104 @@ wait_for_debug_event (DEBUG_EVENT *event, DWORD timeout)
   return result;
 }
 
-/* Helper template for the CreateProcess wrappers.  */
+/* Flags to pass to UpdateProcThreadAttribute.  */
+#define relocate_aslr_flags ((0x2 << 8) | (0x2 << 16))
+
+/* Attribute to pass to UpdateProcThreadAttribute.  */
+#define mitigation_policy 0x00020007
+
+/* Pick one of the symbols as a sentinel.  */
+#ifdef PROCESS_CREATION_MITIGATION_POLICY_FORCE_RELOCATE_IMAGES_ALWAYS_OFF
+
+static_assert ((PROCESS_CREATION_MITIGATION_POLICY_FORCE_RELOCATE_IMAGES_ALWAYS_OFF
+		| PROCESS_CREATION_MITIGATION_POLICY_BOTTOM_UP_ASLR_ALWAYS_OFF)
+	       == relocate_aslr_flags,
+	       "check that ASLR flag values are correct");
+
+static_assert (PROC_THREAD_ATTRIBUTE_MITIGATION_POLICY == mitigation_policy,
+	       "check that mitigation policy value is correct");
+
+#endif
+
+/* Helper template for the CreateProcess wrappers.
+
+   FUNC is the type of the underlying CreateProcess call.  CHAR is the
+   character type to use, and INFO is the "startupinfo" type to use.
+
+   DO_CREATE_PROCESS is the underlying CreateProcess function to use;
+   the remaining arguments are passed to it.  */
 template<typename FUNC, typename CHAR, typename INFO>
 BOOL
 create_process_wrapper (FUNC *do_create_process, const CHAR *image,
 			CHAR *command_line, DWORD flags,
 			void *environment, const CHAR *cur_dir,
+			bool no_randomization,
 			INFO *startup_info,
 			PROCESS_INFORMATION *process_info)
 {
+  if (no_randomization && disable_randomization_available ())
+    {
+      static bool tried_and_failed;
+
+      if (!tried_and_failed)
+	{
+	  /* Windows 8 is required for the real declaration, but to
+	     allow building on earlier versions of Windows, we declare
+	     the type locally.  */
+	  struct gdb_extended_info
+	  {
+	    INFO StartupInfo;
+	    gdb_lpproc_thread_attribute_list lpAttributeList;
+	  };
+
+	  gdb_extended_info info_ex {};
+
+	  if (startup_info != nullptr)
+	    info_ex.StartupInfo = *startup_info;
+	  info_ex.StartupInfo.cb = sizeof (info_ex);
+	  SIZE_T size = 0;
+	  /* Ignore the result here.  The documentation says the first
+	     call always fails, by design.  */
+	  InitializeProcThreadAttributeList (nullptr, 1, 0, &size);
+	  info_ex.lpAttributeList
+	    = (PPROC_THREAD_ATTRIBUTE_LIST) alloca (size);
+	  InitializeProcThreadAttributeList (info_ex.lpAttributeList,
+					     1, 0, &size);
+
+	  gdb::optional<BOOL> return_value;
+	  DWORD attr_flags = relocate_aslr_flags;
+	  if (!UpdateProcThreadAttribute (info_ex.lpAttributeList, 0,
+					  mitigation_policy,
+					  &attr_flags,
+					  sizeof (attr_flags),
+					  nullptr, nullptr))
+	    tried_and_failed = true;
+	  else
+	    {
+	      BOOL result = do_create_process (image, command_line,
+					       nullptr, nullptr,
+					       TRUE,
+					       (flags
+						| EXTENDED_STARTUPINFO_PRESENT),
+					       environment,
+					       cur_dir,
+					       (STARTUPINFO *) &info_ex,
+					       process_info);
+	      if (result)
+		return_value = result;
+	      else if (GetLastError () == ERROR_INVALID_PARAMETER)
+		tried_and_failed = true;
+	      else
+		return_value = FALSE;
+	    }
+
+	  DeleteProcThreadAttributeList (info_ex.lpAttributeList);
+
+	  if (return_value.has_value ())
+	    return *return_value;
+	}
+    }
+
   return do_create_process (image,
 			    command_line, /* command line */
 			    nullptr,	  /* Security */
@@ -767,11 +860,12 @@ create_process_wrapper (FUNC *do_create_process, const CHAR *image,
 BOOL
 create_process (const char *image, char *command_line, DWORD flags,
 		void *environment, const char *cur_dir,
+		bool no_randomization,
 		STARTUPINFOA *startup_info,
 		PROCESS_INFORMATION *process_info)
 {
   return create_process_wrapper (CreateProcessA, image, command_line, flags,
-				 environment, cur_dir,
+				 environment, cur_dir, no_randomization,
 				 startup_info, process_info);
 }
 
@@ -782,11 +876,12 @@ create_process (const char *image, char *command_line, DWORD flags,
 BOOL
 create_process (const wchar_t *image, wchar_t *command_line, DWORD flags,
 		void *environment, const wchar_t *cur_dir,
+		bool no_randomization,
 		STARTUPINFOW *startup_info,
 		PROCESS_INFORMATION *process_info);
 {
   return create_process_wrapper (CreateProcessW, image, command_line, flags,
-				 environment, cur_dir,
+				 environment, cur_dir, no_randomization,
 				 startup_info, process_info);
 }
 
@@ -827,6 +922,16 @@ bad_GetConsoleFontSize (HANDLE w, DWORD nFont)
 /* See windows-nat.h.  */
 
 bool
+disable_randomization_available ()
+{
+  return (InitializeProcThreadAttributeList != nullptr
+	  && UpdateProcThreadAttribute != nullptr
+	  && DeleteProcThreadAttributeList != nullptr);
+}
+
+/* See windows-nat.h.  */
+
+bool
 initialize_loadable ()
 {
   bool result = true;
@@ -852,6 +957,10 @@ initialize_loadable ()
 #endif
       GPA (hm, GenerateConsoleCtrlEvent);
       GPA (hm, GetThreadDescription);
+
+      GPA (hm, InitializeProcThreadAttributeList);
+      GPA (hm, UpdateProcThreadAttribute);
+      GPA (hm, DeleteProcThreadAttributeList);
     }
 
   /* Set variables to dummy versions of these processes if the function
diff --git a/gdb/nat/windows-nat.h b/gdb/nat/windows-nat.h
index d8c498ef06e..65b789fa593 100644
--- a/gdb/nat/windows-nat.h
+++ b/gdb/nat/windows-nat.h
@@ -294,17 +294,21 @@ extern BOOL continue_last_debug_event (DWORD continue_status,
 
 extern BOOL wait_for_debug_event (DEBUG_EVENT *event, DWORD timeout);
 
-/* Wrappers for CreateProcess.  */
+/* Wrappers for CreateProcess.  These exist primarily so that the
+   "disable randomization" feature can be implemented in a single
+   place.  */
 
 extern BOOL create_process (const char *image, char *command_line,
 			    DWORD flags, void *environment,
 			    const char *cur_dir,
+			    bool no_randomization,
 			    STARTUPINFOA *startup_info,
 			    PROCESS_INFORMATION *process_info);
 #ifdef __CYGWIN__
 extern BOOL create_process (const wchar_t *image, wchar_t *command_line,
 			    DWORD flags, void *environment,
 			    const wchar_t *cur_dir,
+			    bool no_randomization,
 			    STARTUPINFOW *startup_info,
 			    PROCESS_INFORMATION *process_info);
 #endif /* __CYGWIN__ */
@@ -313,10 +317,15 @@ extern BOOL create_process (const wchar_t *image, wchar_t *command_line,
 #define DebugActiveProcessStop		dyn_DebugActiveProcessStop
 #define DebugBreakProcess		dyn_DebugBreakProcess
 #define DebugSetProcessKillOnExit	dyn_DebugSetProcessKillOnExit
+#undef EnumProcessModules
 #define EnumProcessModules		dyn_EnumProcessModules
+#undef EnumProcessModulesEx
 #define EnumProcessModulesEx		dyn_EnumProcessModulesEx
+#undef GetModuleInformation
 #define GetModuleInformation		dyn_GetModuleInformation
+#undef GetModuleFileNameExA
 #define GetModuleFileNameExA		dyn_GetModuleFileNameExA
+#undef GetModuleFileNameExW
 #define GetModuleFileNameExW		dyn_GetModuleFileNameExW
 #define LookupPrivilegeValueA		dyn_LookupPrivilegeValueA
 #define OpenProcessToken		dyn_OpenProcessToken
@@ -327,6 +336,9 @@ extern BOOL create_process (const wchar_t *image, wchar_t *command_line,
 #define Wow64SetThreadContext		dyn_Wow64SetThreadContext
 #define Wow64GetThreadSelectorEntry	dyn_Wow64GetThreadSelectorEntry
 #define GenerateConsoleCtrlEvent	dyn_GenerateConsoleCtrlEvent
+#define InitializeProcThreadAttributeList dyn_InitializeProcThreadAttributeList
+#define UpdateProcThreadAttribute dyn_UpdateProcThreadAttribute
+#define DeleteProcThreadAttributeList dyn_DeleteProcThreadAttributeList
 
 typedef BOOL WINAPI (AdjustTokenPrivileges_ftype) (HANDLE, BOOL,
 						   PTOKEN_PRIVILEGES,
@@ -397,6 +409,30 @@ extern Wow64GetThreadSelectorEntry_ftype *Wow64GetThreadSelectorEntry;
 typedef BOOL WINAPI (GenerateConsoleCtrlEvent_ftype) (DWORD, DWORD);
 extern GenerateConsoleCtrlEvent_ftype *GenerateConsoleCtrlEvent;
 
+/* We use a local typedef for this type to avoid depending on
+   Windows 8.  */
+typedef void *gdb_lpproc_thread_attribute_list;
+
+typedef BOOL WINAPI (InitializeProcThreadAttributeList_ftype)
+     (gdb_lpproc_thread_attribute_list lpAttributeList,
+      DWORD dwAttributeCount, DWORD dwFlags, PSIZE_T lpSize);
+extern InitializeProcThreadAttributeList_ftype *InitializeProcThreadAttributeList;
+
+typedef BOOL WINAPI (UpdateProcThreadAttribute_ftype)
+     (gdb_lpproc_thread_attribute_list lpAttributeList,
+      DWORD dwFlags, DWORD_PTR Attribute, PVOID lpValue, SIZE_T cbSize,
+      PVOID lpPreviousValue, PSIZE_T lpReturnSize);
+extern UpdateProcThreadAttribute_ftype *UpdateProcThreadAttribute;
+
+typedef void WINAPI (DeleteProcThreadAttributeList_ftype)
+     (gdb_lpproc_thread_attribute_list lpAttributeList);
+extern DeleteProcThreadAttributeList_ftype *DeleteProcThreadAttributeList;
+
+/* Return true if it's possible to disable randomization on this
+   host.  */
+
+extern bool disable_randomization_available ();
+
 /* Load any functions which may not be available in ancient versions
    of Windows.  */
 
diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 262619d9cb7..0f9fde9f804 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -281,6 +281,11 @@ struct windows_nat_target final : public x86_nat_target<inf_child_target>
   int get_windows_debug_event (int pid, struct target_waitstatus *ourstatus);
 
   void do_initial_windows_stuff (DWORD pid, bool attaching);
+
+  bool supports_disable_randomization () override
+  {
+    return disable_randomization_available ();
+  }
 };
 
 static windows_nat_target the_windows_nat_target;
@@ -2493,6 +2498,7 @@ windows_nat_target::create_inferior (const char *exec_file,
   windows_init_thread_list ();
   ret = create_process (args, flags, w32_env,
 			inferior_cwd != nullptr ? infcwd : nullptr,
+			disable_randomization,
 			&si, &pi);
   if (w32_env)
     /* Just free the Win32 environment, if it could be created. */
@@ -2612,6 +2618,7 @@ windows_nat_target::create_inferior (const char *exec_file,
 			flags,	/* start flags */
 			w32env,	/* environment */
 			inferior_cwd, /* current directory */
+			disable_randomization,
 			&si,
 			&pi);
   if (tty != INVALID_HANDLE_VALUE)
diff --git a/gdbserver/win32-low.cc b/gdbserver/win32-low.cc
index 00ce2a52feb..a9af6467d7c 100644
--- a/gdbserver/win32-low.cc
+++ b/gdbserver/win32-low.cc
@@ -586,6 +586,7 @@ create_process (const char *program, char *args,
 			(inferior_cwd.empty ()
 			 ? NULL
 			 : gdb_tilde_expand (inferior_cwd.c_str ()).c_str()),
+			get_client_state ().disable_randomization,
 			&si,               /* start info */
 			pi);               /* proc info */
 
diff --git a/gdbserver/win32-low.h b/gdbserver/win32-low.h
index d16f1f9609c..b29e8b3a10a 100644
--- a/gdbserver/win32-low.h
+++ b/gdbserver/win32-low.h
@@ -165,6 +165,11 @@ public:
   { return true; }
 
   const char *pid_to_exec_file (int pid) override;
+
+  bool supports_disable_randomization () override
+  {
+    return windows_nat::disable_randomization_available ();
+  }
 };
 
 /* The sole Windows process.  */