[RuntimeDyld] Fixed buffer overflows with absolute symbols

Differential Revision: https://reviews.llvm.org/D95596

Author: MoritzS

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyld.cpp

@@ -146,8 +146,8 @@ void RuntimeDyldImpl::resolveLocalRelocations() {
     // The Section here (Sections[i]) refers to the section in which the
     // symbol for the relocation is located.  The SectionID in the relocation
     // entry provides the section to which the relocation will be applied.
-    int Idx = it->first;
-    uint64_t Addr = Sections[Idx].getLoadAddress();
+    unsigned Idx = it->first;
+    uint64_t Addr = getSectionLoadAddress(Idx);
     LLVM_DEBUG(dbgs() << "Resolving relocations Section #" << Idx << "\t"
                       << format("%p", (uintptr_t)Addr) << "\n");
     resolveRelocationList(it->second, Addr);
@@ -1077,7 +1077,8 @@ void RuntimeDyldImpl::resolveRelocationList(const RelocationList &Relocs,
   for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
     const RelocationEntry &RE = Relocs[i];
     // Ignore relocations for sections that were not loaded
-    if (Sections[RE.SectionID].getAddress() == nullptr)
+    if (RE.SectionID != AbsoluteSymbolSection &&
+        Sections[RE.SectionID].getAddress() == nullptr)
       continue;
     resolveRelocation(RE, Value);
   }

llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h

@@ -462,16 +462,26 @@ class RuntimeDyldImpl {
   loadObject(const object::ObjectFile &Obj) = 0;
 
   uint64_t getSectionLoadAddress(unsigned SectionID) const {
-    return Sections[SectionID].getLoadAddress();
+    if (SectionID == AbsoluteSymbolSection)
+      return 0;
+    else
+      return Sections[SectionID].getLoadAddress();
   }
 
   uint8_t *getSectionAddress(unsigned SectionID) const {
-    return Sections[SectionID].getAddress();
+    if (SectionID == AbsoluteSymbolSection)
+      return nullptr;
+    else
+      return Sections[SectionID].getAddress();
   }
 
   StringRef getSectionContent(unsigned SectionID) const {
-    return StringRef(reinterpret_cast<char *>(Sections[SectionID].getAddress()),
-                     Sections[SectionID].getStubOffset() + getMaxStubSize());
+    if (SectionID == AbsoluteSymbolSection)
+      return {};
+    else
+      return StringRef(
+          reinterpret_cast<char *>(Sections[SectionID].getAddress()),
+          Sections[SectionID].getStubOffset() + getMaxStubSize());
   }
 
   uint8_t* getSymbolLocalAddress(StringRef Name) const {
@@ -519,9 +529,7 @@ class RuntimeDyldImpl {
 
     for (auto &KV : GlobalSymbolTable) {
       auto SectionID = KV.second.getSectionID();
-      uint64_t SectionAddr = 0;
-      if (SectionID != AbsoluteSymbolSection)
-        SectionAddr = getSectionLoadAddress(SectionID);
+      uint64_t SectionAddr = getSectionLoadAddress(SectionID);
       Result[KV.first()] =
         JITEvaluatedSymbol(SectionAddr + KV.second.getOffset(), KV.second.getFlags());
     }