[runtimes][PAC] Harden unwinding when possible (llvm#143230)

This hardens the unwinding logic and datastructures on systems
that support pointer authentication.

The approach taken to hardening is to harden the schemas of as many
high value fields in the myriad structs as possible, and then also
explicitly qualify local variables referencing privileged or security
critical values.

This does introduce ABI linkage between libcxx, libcxxabi, and
libunwind but those are in principle separate from the OS itself
so we've kept the schema definitions in the library specific headers
rather than ptrauth.h

Author: ojhunt

compiler-rt/lib/builtins/gcc_personality_v0.c

@@ -30,6 +30,54 @@ EXCEPTION_DISPOSITION _GCC_specific_handler(PEXCEPTION_RECORD, void *, PCONTEXT,
                                             _Unwind_Personality_Fn);
 #endif
 
+#if __has_feature(ptrauth_calls)
+#include <ptrauth.h>
+
+// `__ptrauth_restricted_intptr` is a feature of apple clang that predates
+// support for direct application of `__ptrauth` to integer types. This
+// guard is necessary to support compilation with those compiler.
+#if __has_feature(ptrauth_restricted_intptr_qualifier)
+#define __ptrauth_gcc_personality_intptr(key, addressDiscriminated,            \
+                                         discriminator)                        \
+  __ptrauth_restricted_intptr(key, addressDiscriminated, discriminator)
+#else
+#define __ptrauth_gcc_personality_intptr(key, addressDiscriminated,            \
+                                         discriminator)                        \
+  __ptrauth(key, addressDiscriminated, discriminator)
+#endif
+#else
+#define __ptrauth_gcc_personality_intptr(...)
+#endif
+
+#define __ptrauth_gcc_personality_func_key ptrauth_key_function_pointer
+
+// ptrauth_string_discriminator("__gcc_personality_v0'funcStart") == 0xDFEB
+#define __ptrauth_gcc_personality_func_start                                   \
+  __ptrauth_gcc_personality_intptr(__ptrauth_gcc_personality_func_key, 1,      \
+                                   0xDFEB)
+
+// ptrauth_string_discriminator("__gcc_personality_v0'start") == 0x52DC
+#define __ptrauth_gcc_personality_start                                        \
+  __ptrauth_gcc_personality_intptr(__ptrauth_gcc_personality_func_key, 1,      \
+                                   0x52DC)
+
+// ptrauth_string_discriminator("__gcc_personality_v0'length") == 0xFFF7
+#define __ptrauth_gcc_personality_length                                       \
+  __ptrauth_gcc_personality_intptr(__ptrauth_gcc_personality_func_key, 1,      \
+                                   0xFFF7)
+
+// ptrauth_string_discriminator("__gcc_personality_v0'landingPadOffset") ==
+// 0x6498
+#define __ptrauth_gcc_personality_lpoffset                                     \
+  __ptrauth_gcc_personality_intptr(__ptrauth_gcc_personality_func_key, 1,      \
+                                   0x6498)
+
+// ptrauth_string_discriminator("__gcc_personality_v0'landingPad") == 0xA134
+#define __ptrauth_gcc_personality_lpad_disc 0xA134
+#define __ptrauth_gcc_personality_lpad                                         \
+  __ptrauth_gcc_personality_intptr(__ptrauth_gcc_personality_func_key, 1,      \
+                                   __ptrauth_gcc_personality_lpad_disc)
+
 // Pointer encodings documented at:
 //   http://refspecs.freestandards.org/LSB_1.3.0/gLSB/gLSB/ehframehdr.html
 
@@ -205,7 +253,8 @@ COMPILER_RT_ABI _Unwind_Reason_Code __gcc_personality_v0(
     return continueUnwind(exceptionObject, context);
 
   uintptr_t pc = (uintptr_t)_Unwind_GetIP(context) - 1;
-  uintptr_t funcStart = (uintptr_t)_Unwind_GetRegionStart(context);
+  uintptr_t __ptrauth_gcc_personality_func_start funcStart =
+      (uintptr_t)_Unwind_GetRegionStart(context);
   uintptr_t pcOffset = pc - funcStart;
 
   // Parse LSDA header.
@@ -224,11 +273,14 @@ COMPILER_RT_ABI _Unwind_Reason_Code __gcc_personality_v0(
   const uint8_t *callSiteTableEnd = callSiteTableStart + callSiteTableLength;
   const uint8_t *p = callSiteTableStart;
   while (p < callSiteTableEnd) {
-    uintptr_t start = readEncodedPointer(&p, callSiteEncoding);
-    size_t length = readEncodedPointer(&p, callSiteEncoding);
-    size_t landingPad = readEncodedPointer(&p, callSiteEncoding);
+    uintptr_t __ptrauth_gcc_personality_start start =
+        readEncodedPointer(&p, callSiteEncoding);
+    size_t __ptrauth_gcc_personality_length length =
+        readEncodedPointer(&p, callSiteEncoding);
+    size_t __ptrauth_gcc_personality_lpoffset landingPadOffset =
+        readEncodedPointer(&p, callSiteEncoding);
     readULEB128(&p); // action value not used for C code
-    if (landingPad == 0)
+    if (landingPadOffset == 0)
       continue; // no landing pad for this entry
     if ((start <= pcOffset) && (pcOffset < (start + length))) {
       // Found landing pad for the PC.
@@ -238,7 +290,24 @@ COMPILER_RT_ABI _Unwind_Reason_Code __gcc_personality_v0(
       _Unwind_SetGR(context, __builtin_eh_return_data_regno(0),
                     (uintptr_t)exceptionObject);
       _Unwind_SetGR(context, __builtin_eh_return_data_regno(1), 0);
-      _Unwind_SetIP(context, (funcStart + landingPad));
+      size_t __ptrauth_gcc_personality_lpad landingPad =
+          funcStart + landingPadOffset;
+#if __has_feature(ptrauth_calls)
+      uintptr_t stackPointer = _Unwind_GetGR(context, -2);
+      const uintptr_t existingDiscriminator = ptrauth_blend_discriminator(
+          &landingPad, __ptrauth_gcc_personality_lpad_disc);
+      // newIP is authenticated as if it were qualified with a pseudo qualifier
+      // along the lines of:
+      //   __ptrauth(ptrauth_key_return_address, <stackPointer>, 0)
+      // where the stack pointer is used in place of the strict storage
+      // address.
+      uintptr_t newIP = (uintptr_t)ptrauth_auth_and_resign(
+          *(void **)&landingPad, __ptrauth_gcc_personality_func_key,
+          existingDiscriminator, ptrauth_key_return_address, stackPointer);
+      _Unwind_SetIP(context, newIP);
+#else
+      _Unwind_SetIP(context, landingPad);
+#endif
       return _URC_INSTALL_CONTEXT;
     }
   }

libcxxabi/include/__cxxabi_config.h

@@ -103,6 +103,47 @@
 #define _LIBCXXABI_DTOR_FUNC
 #endif
 
+#if __has_include(<ptrauth.h>)
+#  include <ptrauth.h>
+#endif
+
+#if __has_feature(ptrauth_calls)
+
+// ptrauth_string_discriminator("__cxa_exception::actionRecord") == 0xFC91
+#  define __ptrauth_cxxabi_action_record __ptrauth(ptrauth_key_process_dependent_data, 1, 0xFC91)
+
+// ptrauth_string_discriminator("__cxa_exception::languageSpecificData") == 0xE8EE
+#  define __ptrauth_cxxabi_lsd __ptrauth(ptrauth_key_process_dependent_data, 1, 0xE8EE)
+
+// ptrauth_string_discriminator("__cxa_exception::catchTemp") == 0xFA58
+#  define __ptrauth_cxxabi_catch_temp_disc 0xFA58
+#  define __ptrauth_cxxabi_catch_temp_key ptrauth_key_process_dependent_data
+#  define __ptrauth_cxxabi_catch_temp __ptrauth(__ptrauth_cxxabi_catch_temp_key, 1, __ptrauth_cxxabi_catch_temp_disc)
+
+// ptrauth_string_discriminator("__cxa_exception::adjustedPtr") == 0x99E4
+#  define __ptrauth_cxxabi_adjusted_ptr __ptrauth(ptrauth_key_process_dependent_data, 1, 0x99E4)
+
+// ptrauth_string_discriminator("__cxa_exception::unexpectedHandler") == 0x99A9
+#  define __ptrauth_cxxabi_unexpected_handler __ptrauth(ptrauth_key_function_pointer, 1, 0x99A9)
+
+// ptrauth_string_discriminator("__cxa_exception::terminateHandler") == 0x0886)
+#  define __ptrauth_cxxabi_terminate_handler __ptrauth(ptrauth_key_function_pointer, 1, 0x886)
+
+// ptrauth_string_discriminator("__cxa_exception::exceptionDestructor") == 0xC088
+#  define __ptrauth_cxxabi_exception_destructor __ptrauth(ptrauth_key_function_pointer, 1, 0xC088)
+
+#else
+
+#  define __ptrauth_cxxabi_action_record
+#  define __ptrauth_cxxabi_lsd
+#  define __ptrauth_cxxabi_catch_temp
+#  define __ptrauth_cxxabi_adjusted_ptr
+#  define __ptrauth_cxxabi_unexpected_handler
+#  define __ptrauth_cxxabi_terminate_handler
+#  define __ptrauth_cxxabi_exception_destructor
+
+#endif
+
 #if __cplusplus < 201103L
 #  define _LIBCXXABI_NOEXCEPT throw()
 #else

libcxxabi/src/cxa_exception.cpp

@@ -192,7 +192,9 @@ void *__cxa_allocate_exception(size_t thrown_size) throw() {
         std::terminate();
     __cxa_exception *exception_header =
         static_cast<__cxa_exception *>((void *)(raw_buffer + header_offset));
-    ::memset(exception_header, 0, actual_size);
+    // We warn on memset to a non-trivially castable type. We might want to
+    // change that diagnostic to not fire on a trivially obvious zero fill.
+    ::memset(static_cast<void*>(exception_header), 0, actual_size);
     return thrown_object_from_cxa_exception(exception_header);
 }
 

libcxxabi/src/cxa_exception.h

@@ -47,10 +47,10 @@ struct _LIBCXXABI_HIDDEN __cxa_exception {
     // In Wasm, a destructor returns its argument
     void *(_LIBCXXABI_DTOR_FUNC *exceptionDestructor)(void *);
 #else
-    void (_LIBCXXABI_DTOR_FUNC *exceptionDestructor)(void *);
+    void (_LIBCXXABI_DTOR_FUNC *__ptrauth_cxxabi_exception_destructor exceptionDestructor)(void *);
 #endif
-    std::unexpected_handler unexpectedHandler;
-    std::terminate_handler  terminateHandler;
+    std::unexpected_handler __ptrauth_cxxabi_unexpected_handler unexpectedHandler;
+    std::terminate_handler __ptrauth_cxxabi_terminate_handler terminateHandler;
 
     __cxa_exception *nextException;
 
@@ -61,10 +61,10 @@ struct _LIBCXXABI_HIDDEN __cxa_exception {
     int propagationCount;
 #else
     int handlerSwitchValue;
-    const unsigned char *actionRecord;
-    const unsigned char *languageSpecificData;
-    void *catchTemp;
-    void *adjustedPtr;
+    const unsigned char *__ptrauth_cxxabi_action_record actionRecord;
+    const unsigned char *__ptrauth_cxxabi_lsd languageSpecificData;
+    void *__ptrauth_cxxabi_catch_temp catchTemp;
+    void *__ptrauth_cxxabi_adjusted_ptr adjustedPtr;
 #endif
 
 #if !defined(__LP64__) && !defined(_WIN64) && !defined(_LIBCXXABI_ARM_EHABI)
@@ -79,16 +79,18 @@ struct _LIBCXXABI_HIDDEN __cxa_exception {
 // http://sourcery.mentor.com/archives/cxx-abi-dev/msg01924.html
 // The layout of this structure MUST match the layout of __cxa_exception, with
 // primaryException instead of referenceCount.
+// The pointer authentication schemas specified here must also match those of
+// the corresponding members in __cxa_exception.
 struct _LIBCXXABI_HIDDEN __cxa_dependent_exception {
 #if defined(__LP64__) || defined(_WIN64) || defined(_LIBCXXABI_ARM_EHABI)
     void* reserve; // padding.
     void* primaryException;
 #endif
 
     std::type_info *exceptionType;
-    void (_LIBCXXABI_DTOR_FUNC *exceptionDestructor)(void *);
-    std::unexpected_handler unexpectedHandler;
-    std::terminate_handler terminateHandler;
+    void (_LIBCXXABI_DTOR_FUNC *__ptrauth_cxxabi_exception_destructor exceptionDestructor)(void *);
+    std::unexpected_handler __ptrauth_cxxabi_unexpected_handler unexpectedHandler;
+    std::terminate_handler __ptrauth_cxxabi_terminate_handler terminateHandler;
 
     __cxa_exception *nextException;
 
@@ -99,10 +101,10 @@ struct _LIBCXXABI_HIDDEN __cxa_dependent_exception {
     int propagationCount;
 #else
     int handlerSwitchValue;
-    const unsigned char *actionRecord;
-    const unsigned char *languageSpecificData;
-    void * catchTemp;
-    void *adjustedPtr;
+    const unsigned char *__ptrauth_cxxabi_action_record actionRecord;
+    const unsigned char *__ptrauth_cxxabi_lsd languageSpecificData;
+    void *__ptrauth_cxxabi_catch_temp catchTemp;
+    void *__ptrauth_cxxabi_adjusted_ptr adjustedPtr;
 #endif
 
 #if !defined(__LP64__) && !defined(_WIN64) && !defined(_LIBCXXABI_ARM_EHABI)