[ELF] - Added support of PT_OPENBSD_RANDOMIZE

[grimar]

Summary

This is 30646.

PT_OPENBSD_RANDOMIZE
The array element specifies the location and size of a part of the memory image of the program that must be filled with random data before any code in the object is executed. The memory region specified by a segment of this type may overlap the region specified by a PT_GNU_RELRO segment, in which case the intersection will be filled with random data before being marked read-only.

Reference links:
http://man.openbsd.org/OpenBSD-current/man5/elf.5
https://github.com/openbsd/src/commit/c494713c450d98da3f2e1451ee8c7fb675a7c461

[ruiu]

I wonder if you tried the new tests with ld.bfd with the openbsd-local patch to see that the tests are valid.

[grimar]

In D25469#567487, @ruiu wrote:

I wonder if you tried the new tests with ld.bfd with the openbsd-local patch to see that the tests are valid.

Just tries to do that. Used binutils-2.17.50 and applied changes from next 2 patches:
https://github.com/openbsd/src/commit/c494713c450d98da3f2e1451ee8c7fb675a7c461
https://github.com/openbsd/src/commit/ce234db7935b2890e0880e442d2a68b8f25b2c93

Link result I observed was similar to result shown in my testcases.

[ruiu]

LGTM

test/ELF/linkerscript/openbsd-randomize.s

9

You want to improve llvm-readobj to print out the name of this hex value.

test/ELF/openbsd_randomize.s

1

Rename openbsd_randomize.s -> openbsd-randomize.s.

[grimar]

test/ELF/linkerscript/openbsd-randomize.s

9

Yep, I'll do that soon.

ELF/LinkerScript.cpp

unsigned Ret = StringSwitch<unsigned>(Tok)
                      .Case("PT_INTERP", PT_INTERP)
                      .Case("PT_NOTE", PT_NOTE)
                      .Case("PT_SHLIB", PT_SHLIB)
                      .Case("PT_PHDR", PT_PHDR)
                      .Case("PT_TLS", PT_TLS)
                      .Case("PT_GNU_EH_FRAME", PT_GNU_EH_FRAME)
                      .Case("PT_GNU_STACK", PT_GNU_STACK)
                      .Case("PT_GNU_RELRO", PT_GNU_RELRO)
+                     .Case("PT_OPENBSD_RANDOMIZE", PT_OPENBSD_RANDOMIZE)
                      .Default(-1);
 
   if (Ret == (unsigned)-1) {
     setError("invalid program header type: " + Tok);
     return PT_NULL;
   }
   return Ret;
 }

ELF/Writer.cpp

if (RelRo.First)
     Ret.push_back(std::move(RelRo));
 
   // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
   if (!Out<ELFT>::EhFrame->empty() && Out<ELFT>::EhFrameHdr) {
     Phdr &Hdr = *AddHdr(PT_GNU_EH_FRAME, Out<ELFT>::EhFrameHdr->getPhdrFlags());
     Hdr.add(Out<ELFT>::EhFrameHdr);
   }
 
+  // PT_OPENBSD_RANDOMIZE specifies the location and size of a part of the
+  // memory image of the program that must be filled with random data before any
+  // code in the object is executed.
+  if (OutputSectionBase<ELFT> *Sec = findSection(".openbsd.randomdata")) {
+    Phdr &Hdr = *AddHdr(PT_OPENBSD_RANDOMIZE, Sec->getPhdrFlags());
+    Hdr.add(Sec);
+  }
+
   // PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
   if (ARMExidx.First)
     Ret.push_back(std::move(ARMExidx));
 
   // PT_GNU_STACK is a special section to tell the loader to make the
   // pages for the stack non-executable.
   if (!Config->ZExecStack) {
     Phdr &Hdr = *AddHdr(PT_GNU_STACK, PF_R | PF_W);

test/ELF/linkerscript/openbsd-randomize.s

+# RUN: llvm-mc -filetype=obj -triple=i686-unknown-linux %s -o %t.o
+# RUN: echo "PHDRS { text PT_LOAD FILEHDR PHDRS; rand PT_OPENBSD_RANDOMIZE; } \
+# RUN:       SECTIONS { . = SIZEOF_HEADERS; \
+# RUN:         .openbsd.randomdata : { *(.openbsd.randomdata) } : rand }" > %t.script
+# RUN: ld.lld --script %t.script %t.o -o %t
+# RUN: llvm-readobj --program-headers -s %t | FileCheck %s
+
+# CHECK:      ProgramHeader {
+# CHECK:        Type:  (0x65A3DBE6)
+# CHECK-NEXT:   Offset: 0x94
+# CHECK-NEXT:   VirtualAddress: 0x94
+# CHECK-NEXT:   PhysicalAddress: 0x94
+# CHECK-NEXT:   FileSize: 8
+# CHECK-NEXT:   MemSize: 8
+# CHECK-NEXT:   Flags [ (0x4)
+# CHECK-NEXT:     PF_R (0x4)
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Alignment: 1
+# CHECK-NEXT: }
+
+.section .openbsd.randomdata, "a"
+.quad 0

test/ELF/openbsd_randomize.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t
+# RUN: ld.lld %t -o %t.out
+# RUN: llvm-readobj --program-headers %t.out | FileCheck %s
+
+# CHECK:      ProgramHeader {
+# CHECK:        Type:  (0x65A3DBE6)
+# CHECK-NEXT:   Offset: 0x158
+# CHECK-NEXT:   VirtualAddress: 0x10158
+# CHECK-NEXT:   PhysicalAddress: 0x10158
+# CHECK-NEXT:   FileSize: 8
+# CHECK-NEXT:   MemSize: 8
+# CHECK-NEXT:   Flags [ (0x4)
+# CHECK-NEXT:     PF_R (0x4)
+# CHECK-NEXT:   ]
+# CHECK-NEXT:   Alignment: 1
+# CHECK-NEXT: }
+
+.section .openbsd.randomdata, "a"
+.quad 0