[runtimes][PAC] Harden unwinding when possible (#138571)

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 +30,45 @@ EXCEPTION_DISPOSITION _GCC_specific_handler(PEXCEPTION_RECORD, void *, PCONTEXT,
                                             _Unwind_Personality_Fn);
 #endif
 
+#if __has_feature(ptrauth_qualifier)
+#include <ptrauth.h>
+#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 +244,8 @@ 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 +264,14 @@ 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 +281,28 @@ 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_qualifier)
+      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

@@ -48,6 +48,7 @@
   #define _LIBCXXABI_FUNC_VIS __declspec(dllimport)
   #define _LIBCXXABI_TYPE_VIS __declspec(dllimport)
  #endif
+
 #else
  #if !defined(_LIBCXXABI_DISABLE_VISIBILITY_ANNOTATIONS)
   #define _LIBCXXABI_HIDDEN __attribute__((__visibility__("hidden")))
@@ -103,6 +104,52 @@
 #define _LIBCXXABI_DTOR_FUNC
 #endif
 
+#if __has_include(<ptrauth.h>)
+#  include <ptrauth.h>
+#endif
+
+#if __has_extension(ptrauth_qualifier)
+
+// 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 \
+            __ptrauth(ptrauth_key_process_dependent_data, 1, 0xFA58)
+
+// 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.h

@@ -47,10 +47,11 @@ 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 +62,10 @@ 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 +80,19 @@ 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 tags used in the pointer authentication qualifiers also need to 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 +103,11 @@ 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)

libcxxabi/src/cxa_personality.cpp

@@ -21,6 +21,49 @@
 #include "cxa_handlers.h"
 #include "private_typeinfo.h"
 #include "unwind.h"
+#include "libunwind.h"
+
+#if __has_include(<ptrauth.h>)
+#  include <ptrauth.h>
+#endif
+
+#if __has_extension(ptrauth_qualifier)
+// The actual value of the discriminators listed below is not important.
+// The derivation of the constants is only being included for the purpose
+// of maintaining a record of how they were originally produced.
+
+// ptrauth_string_discriminator("scan_results::languageSpecificData") == 0xE50D)
+#define __ptrauth_scan_results_lsd \
+  __ptrauth(ptrauth_key_process_dependent_code, 1, 0xE50D)
+
+// ptrauth_string_discriminator("scan_results::actionRecord") == 0x9823
+#define __ptrauth_scan_results_action_record \
+  __ptrauth(ptrauth_key_process_dependent_code, 1, 0x9823)
+
+// scan result is broken up as we have a manual re-sign that requires each component
+#define __ptrauth_scan_results_landingpad_key ptrauth_key_process_dependent_code
+// ptrauth_string_discriminator("scan_results::landingPad") == 0xD27C
+#define __ptrauth_scan_results_landingpad_disc 0xD27C
+#define __ptrauth_scan_results_landingpad \
+   __ptrauth(__ptrauth_scan_results_landingpad_key, 1, __ptrauth_scan_results_landingpad_disc)
+
+#if __has_extension(__ptrauth_restricted_intptr)
+#define __ptrauth_scan_results_landingpad_intptr \
+   __ptrauth_restricted_intptr(__ptrauth_scan_results_landingpad_key, 1, \
+                               __ptrauth_scan_results_landingpad_disc)
+#else
+#define __ptrauth_scan_results_landingpad_intptr \
+   __ptrauth(__ptrauth_scan_results_landingpad_key, 1, \
+             __ptrauth_scan_results_landingpad_disc)
+#endif
+
+#else
+#define __ptrauth_scan_results_lsd
+#define __ptrauth_scan_results_action_record
+#define __ptrauth_scan_results_landingpad
+#define __ptrauth_scan_results_landingpad_intptr
+#endif
+
 
 // TODO: This is a temporary workaround for libc++abi to recognize that it's being
 // built against LLVM's libunwind. LLVM's libunwind started reporting _LIBUNWIND_VERSION
@@ -527,12 +570,17 @@ get_thrown_object_ptr(_Unwind_Exception* unwind_exception)
 namespace
 {
 
+typedef const uint8_t* __ptrauth_scan_results_lsd lsd_ptr_t;
+typedef const uint8_t* __ptrauth_scan_results_action_record action_ptr_t;
+typedef uintptr_t __ptrauth_scan_results_landingpad_intptr landing_pad_t;
+typedef void* __ptrauth_scan_results_landingpad landing_pad_ptr_t;
+
 struct scan_results
 {
     int64_t        ttypeIndex;   // > 0 catch handler, < 0 exception spec handler, == 0 a cleanup
-    const uint8_t* actionRecord;         // Currently unused.  Retained to ease future maintenance.
-    const uint8_t* languageSpecificData;  // Needed only for __cxa_call_unexpected
-    uintptr_t      landingPad;   // null -> nothing found, else something found
+    action_ptr_t actionRecord;   // Currently unused.  Retained to ease future maintenance.
+    lsd_ptr_t languageSpecificData; // Needed only for __cxa_call_unexpected
+    landing_pad_t landingPad;       // null -> nothing found, else something found
     void*          adjustedPtr;  // Used in cxa_exception.cpp
     _Unwind_Reason_Code reason;  // One of _URC_FATAL_PHASE1_ERROR,
                                  //        _URC_FATAL_PHASE2_ERROR,
@@ -541,7 +589,33 @@ struct scan_results
 };
 
 }  // unnamed namespace
+}
+
+namespace {
+// The logical model for casting authenticated function pointers makes
+// it impossible to directly cast them without breaking the authentication,
+// as a result we need this pair of helpers.
+template <typename PtrType>
+void set_landing_pad_as_ptr(scan_results& results, const PtrType& out) {
+  union {
+    landing_pad_t* as_landing_pad;
+    landing_pad_ptr_t* as_pointer;
+  } u;
+  u.as_landing_pad = &results.landingPad;
+  *u.as_pointer = out;
+}
 
+static const landing_pad_ptr_t& get_landing_pad_as_ptr(const scan_results& results) {
+  union {
+    const landing_pad_t* as_landing_pad;
+    const landing_pad_ptr_t* as_pointer;
+  } u;
+  u.as_landing_pad = &results.landingPad;
+  return *u.as_pointer;
+}
+} // unnamed namespace
+
+extern "C" {
 static
 void
 set_registers(_Unwind_Exception* unwind_exception, _Unwind_Context* context,
@@ -557,7 +631,21 @@ set_registers(_Unwind_Exception* unwind_exception, _Unwind_Context* context,
                 reinterpret_cast<uintptr_t>(unwind_exception));
   _Unwind_SetGR(context, __builtin_eh_return_data_regno(1),
                 static_cast<uintptr_t>(results.ttypeIndex));
+#if __has_feature(ptrauth_qualifier)
+  auto stack_pointer = _Unwind_GetGR(context, UNW_REG_SP);
+  // We manually re-sign the IP as the __ptrauth qualifiers cannot
+  // express the required relationship with the destination address
+  const auto existingDiscriminator = ptrauth_blend_discriminator(
+      &results.landingPad, __ptrauth_scan_results_landingpad_disc);
+  unw_word_t newIP /* opaque __ptrauth(ptrauth_key_return_address, stack_pointer, 0) */ =
+      (unw_word_t)ptrauth_auth_and_resign(*(void**)&results.landingPad,
+                                          __ptrauth_scan_results_landingpad_key,
+                                          existingDiscriminator,
+                                          ptrauth_key_return_address, stack_pointer);
+  _Unwind_SetIP(context, newIP);
+#else
   _Unwind_SetIP(context, results.landingPad);
+#endif
 }
 
 /*
@@ -691,12 +779,12 @@ static void scan_eh_tab(scan_results &results, _Unwind_Action actions,
         // The call sites are ordered in increasing value of start
         uintptr_t start = readEncodedPointer(&callSitePtr, callSiteEncoding);
         uintptr_t length = readEncodedPointer(&callSitePtr, callSiteEncoding);
-        uintptr_t landingPad = readEncodedPointer(&callSitePtr, callSiteEncoding);
+        landing_pad_t landingPad = readEncodedPointer(&callSitePtr, callSiteEncoding);
         uintptr_t actionEntry = readULEB128(&callSitePtr);
         if ((start <= ipOffset) && (ipOffset < (start + length)))
 #else  // __USING_SJLJ_EXCEPTIONS__ || __WASM_EXCEPTIONS__
         // ip is 1-based index into this table
-        uintptr_t landingPad = readULEB128(&callSitePtr);
+        landing_pad_t landingPad = readULEB128(&callSitePtr);
         uintptr_t actionEntry = readULEB128(&callSitePtr);
         if (--ip == 0)
 #endif // __USING_SJLJ_EXCEPTIONS__ || __WASM_EXCEPTIONS__
@@ -935,8 +1023,7 @@ __gxx_personality_v0
         results.ttypeIndex = exception_header->handlerSwitchValue;
         results.actionRecord = exception_header->actionRecord;
         results.languageSpecificData = exception_header->languageSpecificData;
-        results.landingPad =
-            reinterpret_cast<uintptr_t>(exception_header->catchTemp);
+        set_landing_pad_as_ptr(results, exception_header->catchTemp);
         results.adjustedPtr = exception_header->adjustedPtr;
 
         // Jump to the handler.
@@ -970,7 +1057,7 @@ __gxx_personality_v0
             exc->handlerSwitchValue = static_cast<int>(results.ttypeIndex);
             exc->actionRecord = results.actionRecord;
             exc->languageSpecificData = results.languageSpecificData;
-            exc->catchTemp = reinterpret_cast<void*>(results.landingPad);
+            exc->catchTemp = get_landing_pad_as_ptr(results);
             exc->adjustedPtr = results.adjustedPtr;
 #ifdef __WASM_EXCEPTIONS__
             // Wasm only uses a single phase (_UA_SEARCH_PHASE), so save the