Bug 628283 - Make elfhack handle GNU_RELRO segments better. r=tglek,a=dbaron

build/unix/elfhack/elf.cpp

@@ -351,6 +351,14 @@ ElfSection *Elf::getSectionAt(unsigned int offset)
     return NULL;
 }
 
+ElfSegment *Elf::getSegmentByType(unsigned int type)
+{
+    for (std::vector<ElfSegment *>::iterator seg = segments.begin(); seg != segments.end(); seg++)
+        if ((*seg)->getType() == type)
+            return *seg;
+    return NULL;
+}
+
 ElfDynamic_Section *Elf::getDynSection()
 {
     for (std::vector<ElfSegment *>::iterator seg = segments.begin(); seg != segments.end(); seg++)
@@ -563,15 +571,28 @@ unsigned int ElfSegment::getFileSize()
     // All sections are SHT_NOBITS
     if (i == sections.rend())
         return 0;
-    return ((*i)->getAddr() - sections.front()->getAddr()) + (*i)->getSize();
+
+    unsigned int end = (*i)->getAddr() + (*i)->getSize();
+
+    // GNU_RELRO segment end is page aligned.
+    if (type == PT_GNU_RELRO)
+        end = (end + 4095) & ~4095;
+
+    return end - sections.front()->getAddr();
 }
 
 unsigned int ElfSegment::getMemSize()
 {
     if (sections.empty())
         return 0;
-    return (sections.back()->getAddr() - sections.front()->getAddr()) +
-           (sections.back()->getSize());
+
+    unsigned int end = sections.back()->getAddr() + sections.back()->getSize();
+
+    // GNU_RELRO segment end is page aligned.
+    if (type == PT_GNU_RELRO)
+        end = (end + 4095) & ~4095;
+
+    return end - sections.front()->getAddr();
 }
 
 ElfSegment *ElfSegment::splitBefore(ElfSection *section)

build/unix/elfhack/elfhack.cpp

@@ -302,6 +302,8 @@ int do_relocation_section(Elf *elf, unsigned int rel_type)
         return -1;
     }
 
+    ElfSegment *relro = elf->getSegmentByType(PT_GNU_RELRO);
+
     ElfRel_Section<Rel_Type> *section = (ElfRel_Section<Rel_Type> *)dyn->getSectionForType(Rel_Type::d_tag);
     assert(section->getType() == Rel_Type::sh_type);
 
@@ -326,7 +328,9 @@ int do_relocation_section(Elf *elf, unsigned int rel_type)
         // Don't pack relocations happening in non writable sections.
         // Our injected code is likely not to be allowed to write there.
         ElfSection *section = elf->getSectionAt(i->r_offset);
-        if (!(section->getFlags() & SHF_WRITE) || (ELF32_R_TYPE(i->r_info) != rel_type))
+        if (!(section->getFlags() & SHF_WRITE) || (ELF32_R_TYPE(i->r_info) != rel_type) ||
+            (relro && (i->r_offset >= relro->getFirstSection()->getAddr()) &&
+                      (i->r_offset < relro->getFirstSection()->getAddr() + relro->getMemSize())))
             new_rels.push_back(*i);
         else {
             // TODO: check that i->r_addend == *i->r_offset

build/unix/elfhack/elfxx.h

@@ -265,6 +265,8 @@ public:
 
     ElfSection *getSectionAt(unsigned int offset);
 
+    ElfSegment *getSegmentByType(unsigned int type);
+
     ElfDynamic_Section *getDynSection();
 
     void write(std::ofstream &file);