[Object/ELF.h] - Improve testing of the fields in ELFFile<ELFT>::sections().

[grimar]

Summary

This eliminates a one error untested and
also introduces a error for one more possible case
which lead to crash previously.

Depends on https://reviews.llvm.org/D64913

[jhenderson]

include/llvm/Object/ELF.h

529

I think this error might be easier to understand with some rewording. How about:

"Invalid section header table offset (e_shoff = 0x1234) or invalid number of sections specified in the first section header's sh_size field (0x4321)."

532

e_shoff should probably be printed in hex, since it's an offset.

test/Object/invalid.test

556

an error

557

How about == instead of =?

593

I think there's one more case to test, if possible: a very high e_shoff value (e.g. 0xfffffffffffffff), combined with a small number of section headers (e.g. 1).

This assumes it's possible in yaml2obj to explicitly specify an e_shoff field without affecting the file size (I can't remember if you added that ability).

[grimar]

• Addressed review comments.

[grimar]

test/Object/invalid.test

593

I had to fix the e_shoff in ELFYAML.h to make this test, it had uint16 type, but had to be uint_X

[jhenderson]

LGTM, with the one suggestion.

include/llvm/Object/ELF.h

524

Prefix these hex numbers with "0x" to make it obvious that they are hex (it's not always obvious).

include/llvm/Object/ELF.h

Expected<typename ELFT::ShdrRange> ELFFile<ELFT>::sections() const {
   const Elf_Shdr *First =
       reinterpret_cast<const Elf_Shdr *>(base() + SectionTableOffset);
 
   uintX_t NumSections = getHeader()->e_shnum;
   if (NumSections == 0)
     NumSections = First->sh_size;
 
   if (NumSections > UINT64_MAX / sizeof(Elf_Shdr))
-    // TODO: this error is untested.
-    return createError("section table goes past the end of file");
+    return createError("invalid number of sections specified in the NULL "
+                       "section's sh_size field (" +
+                       Twine(NumSections) + ")");
 
   const uint64_t SectionTableSize = NumSections * sizeof(Elf_Shdr);
+  if (SectionTableOffset + SectionTableSize < SectionTableOffset)
+    return createError(
+        "invalid section header table offset (e_shoff = " +
+        Twine::utohexstr(SectionTableOffset) +
+        ") or invalid number of sections specified in the first section "
+        "header's sh_size field (" +
+        Twine::utohexstr(NumSections) + ")");
 
   // Section table goes past end of file!
   if (SectionTableOffset + SectionTableSize > FileSize)
     return createError("section table goes past the end of file");
-
   return makeArrayRef(First, NumSections);
 }
 
 template <class ELFT>
 template <typename T>
 Expected<const T *> ELFFile<ELFT>::getEntry(uint32_t Section,
                                             uint32_t Entry) const {
   auto SecOrErr = getSection(Section);
   if (!SecOrErr)

include/llvm/ObjectYAML/ELFYAML.h

struct FileHeader {
   ELF_ELFOSABI OSABI;
   llvm::yaml::Hex8 ABIVersion;
   ELF_ET Type;
   ELF_EM Machine;
   ELF_EF Flags;
   llvm::yaml::Hex64 Entry;
 
   Optional<llvm::yaml::Hex16> SHEntSize;
-  Optional<llvm::yaml::Hex16> SHOffset;
+  Optional<llvm::yaml::Hex64> SHOffset;
   Optional<llvm::yaml::Hex16> SHNum;
   Optional<llvm::yaml::Hex16> SHStrNdx;
 };
 
 struct SectionName {
   StringRef Section;
 };
 

test/Object/invalid.test

FileHeader:
   Class:    ELFCLASS64
   Data:     ELFDATA2LSB
   Type:     ET_REL
   Machine:  EM_X86_64
   SHStrNdx: 0xFF
 Sections:
   - Name: .foo
     Type: SHT_PROGBITS
+
+## We report an error if the number of sections stored in sh_size
+## is greater than UINT64_MAX / sizeof(Elf_Shdr) == 288230376151711743.
+## Here we check that do not crash on a border value.
+
+# RUN: yaml2obj --docnum=26 %s -o %t26
+# RUN: not llvm-readobj -h %t26 2>&1 | FileCheck -DFILE=%t26 --check-prefix=INVALID-SEC-NUM1 %s
+
+# INVALID-SEC-NUM1: error: '[[FILE]]': invalid section header table offset (e_shoff = 40) or invalid number of sections specified in the first section header's sh_size field (3ffffffffffffff)
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+  SHNum:   0x0
+Sections:
+  - Type: SHT_NULL
+    Size: 288230376151711743
+
+## See above, but now we test the UINT64_MAX / sizeof(Elf_Shdr) value.
+## The error is slightly different in this case.
+
+# RUN: yaml2obj --docnum=27 %s -o %t27
+# RUN: not llvm-readobj -h %t27 2>&1 | FileCheck -DFILE=%t27 --check-prefix=INVALID-SEC-NUM2 %s
+
+# INVALID-SEC-NUM2: error: '[[FILE]]': invalid number of sections specified in the NULL section's sh_size field (288230376151711744)
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+  SHNum:   0x0
+Sections:
+  - Type: SHT_NULL
+    Size: 288230376151711744
+
+## Check the case when SHOffset is too large, but SHNum is not. SHOffset + SHNum overflows the uint64 type.
+
+# RUN: yaml2obj --docnum=28 %s -o %t28
+# RUN: not llvm-readobj -h %t28 2>&1 | FileCheck -DFILE=%t28 --check-prefix=INVALID-SEC-NUM3 %s
+
+# INVALID-SEC-NUM3: error: '[[FILE]]': invalid section header table offset (e_shoff = ffffffffffffffff) or invalid number of sections specified in the first section header's sh_size field (1)
+
+--- !ELF
+FileHeader:
+  Class:    ELFCLASS64
+  Data:     ELFDATA2LSB
+  Type:     ET_REL
+  Machine:  EM_X86_64
+  SHOffset: 0xffffffffffffffff
+  SHNum:    0x1

tools/yaml2obj/yaml2elf.cpp

void ELFState<ELFT>::initELFHeader(Elf_Ehdr &Header) {
   Header.e_phentsize = sizeof(Elf_Phdr);
   Header.e_phnum = Doc.ProgramHeaders.size();
 
   Header.e_shentsize =
       Doc.Header.SHEntSize ? (uint16_t)*Doc.Header.SHEntSize : sizeof(Elf_Shdr);
   // Immediately following the ELF header and program headers.
   Header.e_shoff =
       Doc.Header.SHOffset
-          ? (uint16_t)*Doc.Header.SHOffset
+          ? (typename ELFT::uint)(*Doc.Header.SHOffset)
           : sizeof(Header) + sizeof(Elf_Phdr) * Doc.ProgramHeaders.size();
   Header.e_shnum =
       Doc.Header.SHNum ? (uint16_t)*Doc.Header.SHNum : SN2I.size() + 1;
   Header.e_shstrndx = Doc.Header.SHStrNdx ? (uint16_t)*Doc.Header.SHStrNdx
                                           : SN2I.get(".shstrtab");
 }
 
 template <class ELFT>