Recognize and parse GNU Property notes.

GNU Property notes are different from normal notes because they use
variable alignment/padding of their fields. They are 8 byte aligned,
but use 4 byte fields. The name is aligned at 4 bytes and padded so
that, the desc is aligned at 8 bytes. The whole note is padded to
8 bytes again. For normal notes all fields are both 4 bytes wide and
4 bytes aligned.

To recognize these new kind of ELF Notes a new Elf_Type is introduced,
ELF_T_NHDR8. This type is used in the xlate functions to determine
how to align and pad the various fields. Since the fields themselves
can now have different alignments we will have to keep track of the
current alignement and use either NOTE_ALIGN4 or NOTE_ALIGN8 to
determine the padding.

To set the correct Elf_Type on the Elf_Data we use either the section
sh_addralign or the segment p_align values. Assuming 8 means the
section or segment contains the new style notes, otherwise normal
notes.

When we cannot determine the "alignment" directly, like when parsing
special kernel sys files, we check the name "GNU" and type
"GNU_PROPERTY_TYPE_0" fields.

ebl_object_note now parses the new NT_GNU_PROPERTY_TYPE_0 and can
extract the GNU_PROPERTY_STACK_SIZE, GNU_PROPERTY_NO_COPY_ON_PROTECTED
and GNU_PROPERTY_X86_FEATURE_1_AND types GNU_PROPERTY_X86_FEATURE_1_IBT
and GNU_PROPERTY_X86_FEATURE_1_SHSTK.

Tests are added for extracting the note from sections or segments
as set by gcc -fcf-protection.

Signed-off-by: Mark Wielaard <mark@klomp.org>

1 files changed, 14 insertions, 5 deletions

diff --git a/libelf/elf_getdata.c b/libelf/elf_getdata.c
index 278dfa8f..4f80aaf2 100644
--- a/libelf/elf_getdata.c
+++ b/libelf/elf_getdata.c
@@ -65,7 +65,7 @@ static const Elf_Type shtype_map[EV_NUM - 1][TYPEIDX (SHT_HISUNW) + 1] =
       [SHT_PREINIT_ARRAY] = ELF_T_ADDR,
       [SHT_GROUP] = ELF_T_WORD,
       [SHT_SYMTAB_SHNDX] = ELF_T_WORD,
-      [SHT_NOTE] = ELF_T_NHDR,
+      [SHT_NOTE] = ELF_T_NHDR, /* Need alignment to guess ELF_T_NHDR8.  */
       [TYPEIDX (SHT_GNU_verdef)] = ELF_T_VDEF,
       [TYPEIDX (SHT_GNU_verneed)] = ELF_T_VNEED,
       [TYPEIDX (SHT_GNU_versym)] = ELF_T_HALF,
@@ -106,6 +106,7 @@ const uint_fast8_t __libelf_type_aligns[EV_NUM - 1][ELFCLASSNUM - 1][ELF_T_NUM]
       [ELF_T_GNUHASH] = __alignof__ (Elf32_Word),			      \
       [ELF_T_AUXV] = __alignof__ (ElfW2(Bits,auxv_t)),			      \
       [ELF_T_CHDR] = __alignof__ (ElfW2(Bits,Chdr)),			      \
+      [ELF_T_NHDR8] = 8 /* Special case for GNU Property note.  */	      \
     }
     [EV_CURRENT - 1] =
     {
@@ -118,7 +119,7 @@ const uint_fast8_t __libelf_type_aligns[EV_NUM - 1][ELFCLASSNUM - 1][ELF_T_NUM]
 
 Elf_Type
 internal_function
-__libelf_data_type (Elf *elf, int sh_type)
+__libelf_data_type (Elf *elf, int sh_type, GElf_Xword align)
 {
   /* Some broken ELF ABI for 64-bit machines use the wrong hash table
      entry size.  See elf-knowledge.h for more information.  */
@@ -129,7 +130,13 @@ __libelf_data_type (Elf *elf, int sh_type)
       return (SH_ENTSIZE_HASH (ehdr) == 4 ? ELF_T_WORD : ELF_T_XWORD);
     }
   else
-    return shtype_map[LIBELF_EV_IDX][TYPEIDX (sh_type)];
+    {
+      Elf_Type t = shtype_map[LIBELF_EV_IDX][TYPEIDX (sh_type)];
+      /* Special case for GNU Property notes.  */
+      if (t == ELF_T_NHDR && align == 8)
+	t = ELF_T_NHDR8;
+      return t;
+    }
 }
 
 /* Convert the data in the current section.  */
@@ -272,7 +279,9 @@ __libelf_set_rawdata_wrlock (Elf_Scn *scn)
       else
 	{
 	  Elf_Type t = shtype_map[LIBELF_EV_IDX][TYPEIDX (type)];
-	  if (t == ELF_T_VDEF || t == ELF_T_NHDR
+	  if (t == ELF_T_NHDR && align == 8)
+	    t = ELF_T_NHDR8;
+	  if (t == ELF_T_VDEF || t == ELF_T_NHDR || t == ELF_T_NHDR8
 	      || (t == ELF_T_GNUHASH && elf->class == ELFCLASS64))
 	    entsize = 1;
 	  else
@@ -357,7 +366,7 @@ __libelf_set_rawdata_wrlock (Elf_Scn *scn)
   if ((flags & SHF_COMPRESSED) != 0)
     scn->rawdata.d.d_type = ELF_T_CHDR;
   else
-    scn->rawdata.d.d_type = __libelf_data_type (elf, type);
+    scn->rawdata.d.d_type = __libelf_data_type (elf, type, align);
   scn->rawdata.d.d_off = 0;
 
   /* Make sure the alignment makes sense.  d_align should be aligned both