DT_TEXTREL vs IFUNC

If you should somehow link non-pic objects into a PIE or shared
library, resulting in an object with DT_TEXTREL (text relocations)
set, and your executable or shared library also contains GNU indirect
functions, then you're in trouble.  To apply dynamic relocations
ld.so will make the text segment writable.  On most systems this will
make the text segment non-executable, which will then result in a
segfault when ld.so tries to run ifunc resolvers when applying
relocations against ifuncs.

This patch teaches PowerPC ld to detect the situation, and warn.

	* elf64-ppc.c (struct ppc_link_hash_table): Add
	local_ifunc_resolver and maybe_local_ifunc_resolver.
	(ppc_build_one_stub): Set flags on emitting dynamic
	relocation to ifunc.
	(ppc64_elf_relocate_section): Likewise.
	(ppc64_elf_finish_dynamic_symbol): Likewise.
	(ppc64_elf_finish_dynamic_sections): Error on DT_TEXTREL with
	local dynamic relocs to ifuncs.
	* elf32-ppc.c (struct ppc_elf_link_hash_table): Add
	local_ifunc_resolver and maybe_local_ifunc_resolver.
	(ppc_elf_relocate_section): Set flag on emitting dynamic
	relocation to ifuncs.
	(ppc_elf_finish_dynamic_symbol): Likewise.
	(ppc_elf_finish_dynamic_sections): Error on DT_TEXTREL with local
	dynamic relocs to ifuncs.

1 files changed, 53 insertions, 16 deletions

diff --git a/bfd/elf32-ppc.c b/bfd/elf32-ppc.c
index 72ead480c2..4bd58e2696 100644
--- a/bfd/elf32-ppc.c
+++ b/bfd/elf32-ppc.c
@@ -3327,6 +3327,11 @@ struct ppc_elf_link_hash_table
   /* True if the target system is VxWorks.  */
   unsigned int is_vxworks:1;
 
+  /* Whether there exist local gnu indirect function resolvers,
+     referenced by dynamic relocations.  */
+  unsigned int local_ifunc_resolver:1;
+  unsigned int maybe_local_ifunc_resolver:1;
+
   /* The size of PLT entries.  */
   int plt_entry_size;
   /* The distance between adjacent PLT slots.  */
@@ -8386,6 +8391,7 @@ ppc_elf_relocate_section (bfd *output_bfd,
 		  loc += (htab->elf.irelplt->reloc_count++
 			  * sizeof (Elf32_External_Rela));
 		  bfd_elf32_swap_reloca_out (output_bfd, &rela, loc);
+		  htab->local_ifunc_resolver = 1;
 
 		  ent->plt.offset |= 1;
 		}
@@ -8574,7 +8580,13 @@ ppc_elf_relocate_section (bfd *output_bfd,
 			bfd_byte * loc;
 
 			if (ifunc != NULL)
-			  rsec = htab->elf.irelplt;
+			  {
+			    rsec = htab->elf.irelplt;
+			    if (indx == 0)
+			      htab->local_ifunc_resolver = 1;
+			    else if (is_static_defined (h))
+			      htab->maybe_local_ifunc_resolver = 1;
+			  }
 			outrel.r_offset = (htab->elf.sgot->output_section->vma
 					   + htab->elf.sgot->output_offset
 					   + off);
@@ -8867,6 +8879,8 @@ ppc_elf_relocate_section (bfd *output_bfd,
 	      int skip;
 	      bfd_byte *loc;
 	      asection *sreloc;
+	      long indx = 0;
+
 #ifdef DEBUG
 	      fprintf (stderr, "ppc_elf_relocate_section needs to "
 		       "create relocation for %s\n",
@@ -8877,12 +8891,6 @@ ppc_elf_relocate_section (bfd *output_bfd,
 	      /* When generating a shared object, these relocations
 		 are copied into the output file to be resolved at run
 		 time.  */
-	      sreloc = elf_section_data (input_section)->sreloc;
-	      if (ifunc)
-		sreloc = htab->elf.irelplt;
-	      if (sreloc == NULL)
-		return FALSE;
-
 	      skip = 0;
 	      outrel.r_offset = _bfd_elf_section_offset (output_bfd, info,
 							 input_section,
@@ -8900,9 +8908,10 @@ ppc_elf_relocate_section (bfd *output_bfd,
 			    || h->root.type == bfd_link_hash_undefweak))
 		       || !SYMBOL_REFERENCES_LOCAL (info, h))
 		{
-		  BFD_ASSERT (h->dynindx != -1);
+		  indx = h->dynindx;
+		  BFD_ASSERT (indx != -1);
 		  unresolved_reloc = FALSE;
-		  outrel.r_info = ELF32_R_INFO (h->dynindx, r_type);
+		  outrel.r_info = ELF32_R_INFO (indx, r_type);
 		  outrel.r_addend = rel->r_addend;
 		}
 	      else
@@ -8911,8 +8920,6 @@ ppc_elf_relocate_section (bfd *output_bfd,
 
 		  if (r_type != R_PPC_ADDR32)
 		    {
-		      long indx = 0;
-
 		      if (ifunc != NULL)
 			{
 			  /* If we get here when building a static
@@ -8977,6 +8984,18 @@ ppc_elf_relocate_section (bfd *output_bfd,
 		    outrel.r_info = ELF32_R_INFO (0, R_PPC_RELATIVE);
 		}
 
+	      sreloc = elf_section_data (input_section)->sreloc;
+	      if (ifunc)
+		{
+		  sreloc = htab->elf.irelplt;
+		  if (indx == 0)
+		    htab->local_ifunc_resolver = 1;
+		  else if (is_static_defined (h))
+		    htab->maybe_local_ifunc_resolver = 1;
+		}
+	      if (sreloc == NULL)
+		return FALSE;
+
 	      loc = sreloc->contents;
 	      loc += sreloc->reloc_count++ * sizeof (Elf32_External_Rela);
 	      bfd_elf32_swap_reloca_out (output_bfd, &outrel, loc);
@@ -10267,12 +10286,19 @@ ppc_elf_finish_dynamic_symbol (bfd *output_bfd,
 
 	    if (!htab->elf.dynamic_sections_created
 		|| h->dynindx == -1)
-	      loc = (htab->elf.irelplt->contents
-		     + (htab->elf.irelplt->reloc_count++
-			* sizeof (Elf32_External_Rela)));
+	      {
+		loc = (htab->elf.irelplt->contents
+		       + (htab->elf.irelplt->reloc_count++
+			  * sizeof (Elf32_External_Rela)));
+		htab->local_ifunc_resolver = 1;
+	      }
 	    else
-	      loc = (htab->elf.srelplt->contents
-		     + reloc_index * sizeof (Elf32_External_Rela));
+	      {
+		loc = (htab->elf.srelplt->contents
+		       + reloc_index * sizeof (Elf32_External_Rela));
+		if (h->type == STT_GNU_IFUNC && is_static_defined (h))
+		  htab->maybe_local_ifunc_resolver = 1;
+	      }
 	    bfd_elf32_swap_reloca_out (output_bfd, &rela, loc);
 
 	    if (!h->def_regular)
@@ -10477,6 +10503,17 @@ ppc_elf_finish_dynamic_sections (bfd *output_bfd,
 	      dyn.d_un.d_ptr = got;
 	      break;
 
+	    case DT_TEXTREL:
+	      if (htab->local_ifunc_resolver)
+		info->callbacks->einfo
+		  (_("%X%P: text relocations and GNU indirect "
+		     "functions will result in a segfault at runtime\n"));
+	      else if (htab->maybe_local_ifunc_resolver)
+		info->callbacks->einfo
+		  (_("%P: warning: text relocations and GNU indirect "
+		     "functions may result in a segfault at runtime\n"));
+	      continue;
+
 	    default:
 	      if (htab->is_vxworks
 		  && elf_vxworks_finish_dynamic_entry (output_bfd, &dyn))