[llvm-readobj] - Verify the location of program headers better.

[grimar]

Summary

This improves condition in the ELFFile::program_headers().
Previously if was possible to read the headers from the wrong place when
the value of e_phoff was so large that computation overflowed.

[MaskRay]

Thanks!

[jhenderson]

llvm/include/llvm/Object/ELF.h

210

Maybe Offset rather than Off (I'd also take PhOff).

llvm/test/tools/llvm-readobj/ELF/gnu-phdrs.test

389

Either "when the program header table ends" or "when the program headers end"

[jhenderson]

LGTM, with comments.

llvm/include/llvm/Object/ELF.h

public:
 
   Expected<std::vector<Elf_Rela>> android_relas(const Elf_Shdr *Sec) const;
 
   /// Iterate over program header table.
   Expected<Elf_Phdr_Range> program_headers() const {
     if (getHeader()->e_phnum && getHeader()->e_phentsize != sizeof(Elf_Phdr))
       return createError("invalid e_phentsize: " +
                          Twine(getHeader()->e_phentsize));
-    if (getHeader()->e_phoff +
-            (getHeader()->e_phnum * getHeader()->e_phentsize) >
-        getBufSize())
+
+    uint64_t HeadersSize =
+        (uint64_t)getHeader()->e_phnum * getHeader()->e_phentsize;
+    uint64_t PhOff = getHeader()->e_phoff;
+    if (PhOff + HeadersSize < PhOff || PhOff + HeadersSize > getBufSize())
       return createError("program headers are longer than binary of size " +
                          Twine(getBufSize()) + ": e_phoff = 0x" +
                          Twine::utohexstr(getHeader()->e_phoff) +
                          ", e_phnum = " + Twine(getHeader()->e_phnum) +
                          ", e_phentsize = " + Twine(getHeader()->e_phentsize));
-    auto *Begin =
-        reinterpret_cast<const Elf_Phdr *>(base() + getHeader()->e_phoff);
+
+    auto *Begin = reinterpret_cast<const Elf_Phdr *>(base() + PhOff);
     return makeArrayRef(Begin, Begin + getHeader()->e_phnum);
   }
 
   /// Get an iterator over notes in a program header.
   ///
   /// The program header must be of type \c PT_NOTE.
   ///
   /// \param Phdr the program header to iterate over.

llvm/test/tools/llvm-readobj/ELF/gnu-phdrs.test

 ## Case 4: the offset goes 1 byte past the end of the file.
   - Type:   PT_INTERP
     Offset: 563
 ## Case 5: an arbitrary large offset that goes past the end of the file.
   - Type:   PT_INTERP
     Offset: 0xAABBCCDDEEFF1122
 
 ## Check we report a warning when we are unable to read program headers.
-# RUN: yaml2obj --docnum=3 %s -o %t.phdr.err
+## Case A: the e_phentsize field is invalid.
+# RUN: yaml2obj --docnum=3 -DPHENTSIZE=1 %s -o %t.phdr.err
 # RUN: llvm-readelf --program-headers %t.phdr.err 2>&1 | \
 # RUN:   FileCheck %s -DFILE=%t.phdr.err --check-prefix=WARN-PHENTSIZE
 
 # WARN-PHENTSIZE:      Program Headers:
 # WARN-PHENTSIZE-NEXT:   Type Offset VirtAddr PhysAddr FileSiz  MemSiz Flg Align
 # WARN-PHENTSIZE-NEXT: warning: '[[FILE]]': unable to dump program headers: invalid e_phentsize: 1
 # WARN-PHENTSIZE:      Section to Segment mapping:
 # WARN-PHENTSIZE-NEXT:   Segment Sections...
 # WARN-PHENTSIZE-NEXT: warning: '[[FILE]]': can't read program headers to build section to segment mapping: invalid e_phentsize: 1
 
 --- !ELF
 FileHeader:
   Class:      ELFCLASS64
   Data:       ELFDATA2LSB
   Type:       ET_EXEC
   Machine:    EM_X86_64
-  EPhEntSize: 1
+  EPhEntSize: [[PHENTSIZE=56]]
+  EPhOff:     [[PHOFF=64]]
 Sections:
   - Name: .foo
     Type: SHT_PROGBITS
 ProgramHeaders:
   - Type: PT_PHDR
     Sections:
       - Section: .foo
+
+## Case B: the value of the e_phoff field is invalid.
+
+## Check that we do not report a warning when the program header table ends right before the end of the file.
+## 0x160 + size of headers (56) == file size.
+# RUN: yaml2obj --docnum=3 -DPHOFF=0x160 %s -o %t.phdr.no.err2
+# RUN: llvm-readelf %t.phdr.no.err2 --program-headers 2>&1 | FileCheck %s --implicit-check-not=warning:
+
+## Check we report a warning when e_phoff goes 1 byte past the end of the file.
+# RUN: yaml2obj --docnum=3 -DPHOFF=0x161 %s -o %t.phdr.err2
+# RUN: llvm-readelf --program-headers %t.phdr.err2 2>&1 | \
+# RUN:   FileCheck %s -DFILE=%t.phdr.err2 --check-prefix=WARN-PHOFF -DOFF=0x161
+
+# WARN-PHOFF:      Program Headers:
+# WARN-PHOFF-NEXT:   Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
+# WARN-PHOFF-NEXT: warning: '[[FILE]]': unable to dump program headers: program headers are longer than binary of size 408: e_phoff = [[OFF]], e_phnum = 1, e_phentsize = 56
+# WARN-PHOFF:      Section to Segment mapping:
+# WARN-PHOFF-NEXT:   Segment Sections...
+# WARN-PHOFF-NEXT: warning: '[[FILE]]': can't read program headers to build section to segment mapping: program headers are longer than binary of size 408: e_phoff = [[OFF]], e_phnum = 1, e_phentsize = 56
+
+## Check we report a warning when the value of e_phoff is so large that
+## e_phoff + e_phnum * e_phentsize > UINT64_MAX.
+# RUN: yaml2obj --docnum=3 -DPHOFF=0xffffffffffffffff %s -o %t.phdr.err3
+# RUN: llvm-readelf --program-headers %t.phdr.err3 2>&1 | \
+# RUN:   FileCheck %s -DFILE=%t.phdr.err3 --check-prefix=WARN-PHOFF -DOFF=0xffffffffffffffff