add vtable validation

doReadClassName will now first validate that the vtable pointer points to mapped memory before attempting to read it, and throws an exception if it does not

Author: ab9rf

docs/changelog.txt

@@ -61,6 +61,7 @@ Template for new versions:
 ## Fixes
 
 ## Misc Improvements
+- Core: DFHack now validates vtable pointers in objects read from memory and will throw an exception instead of crashing when an invalid vtable pointer is encountered. This makes it easier to identify which DF data structure contains corrupted data when this manifests in the form of a bad vtable pointer, and shifts blame for such crashes from DFHack to DF.
 
 ## Documentation
 

library/DataDefs.cpp

@@ -370,7 +370,7 @@ const virtual_identity *virtual_identity::find(void *vtable)
 
     // If using a reader/writer lock, re-grab as write here, and recheck
     Core &core = Core::getInstance();
-    std::string name = core.p->doReadClassName(vtable);
+    std::string name = core.p->readClassName(vtable);
 
     auto name_it = (*name_lookup).find(name);
     if (name_it != (*name_lookup).end()) {

library/Process.cpp

@@ -236,6 +236,9 @@ Process::~Process()
 
 string Process::doReadClassName (void * vptr)
 {
+    if (!checkValidAddress(vptr))
+        throw std::runtime_error(std::format("invalid vtable ptr {}", vptr));
+
     char* rtti = Process::readPtr(((char*)vptr - sizeof(void*)));
 #ifndef WIN32
     char* typestring = Process::readPtr(rtti + sizeof(void*));
@@ -591,6 +594,20 @@ void Process::getMemRanges(vector<t_memrange>& ranges)
 }
 #endif
 
+bool Process::checkValidAddress(void* ptr)
+{
+    uintptr_t addr = reinterpret_cast<uintptr_t>(ptr);
+    auto validate = [&] (t_memrange& r) {
+        uintptr_t lo = reinterpret_cast<uintptr_t>(r.start);
+        uintptr_t hi = reinterpret_cast<uintptr_t>(r.end);
+        return addr >= lo && addr < hi;
+        };
+    std::vector<t_memrange> mr;
+    getMemRanges(mr);
+    bool valid = std::any_of(mr.begin(), mr.end(), validate);
+    return valid;
+}
+
 uintptr_t Process::getBase()
 {
 #if WIN32

library/include/MemAccess.h

@@ -221,7 +221,7 @@ namespace DFHack
 
         std::string readClassName(void* vptr)
         {
-            std::map<void*, std::string>::iterator it = classNameCache.find(vptr);
+            auto it = classNameCache.find(vptr);
             if (it != classNameCache.end())
                 return it->second;
             return classNameCache[vptr] = doReadClassName(vptr);
@@ -247,6 +247,9 @@ namespace DFHack
         /// get virtual memory ranges of the process (what is mapped where)
         static void getMemRanges(std::vector<t_memrange>& ranges);
 
+        /// check if an address has a mapping
+        bool checkValidAddress(void* ptr);
+
         /// get the symbol table extension of this process
         std::shared_ptr<DFHack::VersionInfo> getDescriptor()
         {