Bug 595033 - nanojit: harden via random function alignment (wmaddox,nnethercote,edwsmith)

Introduce a random number of 'int3' instructions inbetween JIT'd methods.

NOTE: this feature is currently disabled

--HG--
extra : convert_revision : d75d0a918f8e048b92127188f47f4e1efcee9004

js/src/nanojit/Nativei386.cpp

@@ -2815,6 +2815,16 @@ namespace nanojit
         NanoAssert(!_inExit);
         if (!_nIns)
             codeAlloc(codeStart, codeEnd, _nIns verbose_only(, codeBytes));
+
+        // add some random padding, so functions aren't predictably placed.
+        if (_config.harden_function_alignment)
+        {
+            int32_t pad = _noise->getValue(LARGEST_UNDERRUN_PROT);
+            underrunProtect(pad);
+            _nIns -= pad;
+            VMPI_memset(_nIns, INT3_OP, pad);
+            PERFM_NVPROF("hardening:func-align", pad);
+        }
     }
 
     // enough room for n bytes

js/src/nanojit/njconfig.cpp

@@ -92,6 +92,7 @@ namespace nanojit
         i386_use_cmov = (features & (1<<15)) != 0;
         i386_fixed_esp = false;
 #endif
+        harden_function_alignment = false;
 
 #if defined(NANOJIT_ARM)
 

js/src/nanojit/njconfig.h

@@ -94,6 +94,9 @@ namespace nanojit
         // If true, use softfloat for all floating point operations,
         // whether or not an FPU is present. (ARM only for now, but might also includes MIPS in the future)
         uint32_t soft_float:1;
+
+        // If true, compiler will insert a random amount of space in between functions (x86-32 only)
+        uint32_t harden_function_alignment:1;
     };
 }