[PATCH] Handle GNU Build Attribute ELF Notes.

Mark Wielaard mark@klomp.org
Mon Nov 12 23:35:00 GMT 2018


GNU Build Attribute ELF Notes are generated by the GCC annobin plugin
and described at https://fedoraproject.org/wiki/Toolchain/Watermark

Unfortunately the constants aren't yet described in the standard glibc
elf.h so they have been added to the elfutils specific elf-knowledge.h.

The notes abuse the name owner field to encode some data not in the
description. This makes it a bit hard to parse. We have to match the
note owner name prefix (to "GA") to be sure the type is valid. We also
cannot rely on the owner name being a valid C string since the attribute
name and value can contain zero (terminators). So pass around namesz
to the ebl note parsing functions.

eu-elflint will recognize and eu-readelf -n will now show the notes:

Note section [27] '.gnu.build.attributes' of 56080 bytes at offset 0x114564:
  Owner          Data size  Type
  GA                    16  GNU Build Attribute OPEN
    Address Range: 0x2f30f - 0x2f30f
    VERSION: "3p8"
  GA                     0  GNU Build Attribute OPEN
    TOOL: "gcc 8.2.1 20180801"
  GA                     0  GNU Build Attribute OPEN
    "GOW": 45
  GA                     0  GNU Build Attribute OPEN
    STACK_PROT: 0
  GA                     0  GNU Build Attribute OPEN
    "stack_clash": TRUE
  GA                     0  GNU Build Attribute OPEN
    "cf_protection": 0
  GA                     0  GNU Build Attribute OPEN
    "GLIBCXX_ASSERTIONS": TRUE
  GA                     0  GNU Build Attribute OPEN
    "FORTIFY": 0
  GA                     0  GNU Build Attribute OPEN
    PIC: 3
  GA                     0  GNU Build Attribute OPEN
    SHORT_ENUM: FALSE
  GA                     0  GNU Build Attribute OPEN
    ABI: c001100000012
  GA                     0  GNU Build Attribute OPEN
    "stack_realign": FALSE

A new test was added to run-readelf -n for the existing annobin file.

Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 libebl/ChangeLog            |   8 +++
 libebl/eblobjnote.c         | 151 +++++++++++++++++++++++++++++++++++++++++++-
 libebl/eblobjnotetypename.c |  25 +++++++-
 libebl/libebl.h             |   4 +-
 libelf/ChangeLog            |   9 +++
 libelf/elf-knowledge.h      |  21 ++++++
 src/ChangeLog               |   8 +++
 src/elflint.c               |  13 ++++
 src/readelf.c               |  16 ++++-
 tests/ChangeLog             |   4 ++
 tests/run-readelf-n.sh      |  55 ++++++++++++++++
 11 files changed, 308 insertions(+), 6 deletions(-)

diff --git a/libebl/ChangeLog b/libebl/ChangeLog
index 076596f..79a2ff4 100644
--- a/libebl/ChangeLog
+++ b/libebl/ChangeLog
@@ -1,3 +1,11 @@
+2018-11-12  Mark Wielaard  <mark@klomp.org>
+
+	* libebl.h (ebl_object_note): Add new argument namesz.
+	* eblobjnote.c (ebl_object_note): Likewise and handle GNU Build
+	Attribute notes.
+	* eblobjnotetypename.c (ebl_object_note_type_name): Handle GNU
+	Build Attribute notes.
+
 2018-11-11  Mark Wielaard  <mark@klomp.org>
 
 	* eblobjnote.c (ebl_object_note): Recognize NT_VERSION with zero
diff --git a/libebl/eblobjnote.c b/libebl/eblobjnote.c
index 8fda7d9..58ac86d 100644
--- a/libebl/eblobjnote.c
+++ b/libebl/eblobjnote.c
@@ -37,11 +37,14 @@
 #include <string.h>
 #include <libeblP.h>
 
+#include "common.h"
 #include "libelfP.h"
+#include "libdwP.h"
+#include "memory-access.h"
 
 
 void
-ebl_object_note (Ebl *ebl, const char *name, uint32_t type,
+ebl_object_note (Ebl *ebl, uint32_t namesz, const char *name, uint32_t type,
 		 uint32_t descsz, const char *desc)
 {
   if (! ebl->object_note (name, type, descsz, desc))
@@ -135,6 +138,152 @@ ebl_object_note (Ebl *ebl, const char *name, uint32_t type,
 	  return;
 	}
 
+      if (strncmp (name, ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX,
+		   strlen (ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX)) == 0
+	  && (type == NT_GNU_BUILD_ATTRIBUTE_OPEN
+	      || type == NT_GNU_BUILD_ATTRIBUTE_FUNC))
+	{
+	  /* There might or might not be a pair of addresses in the desc.  */
+	  if (descsz > 0)
+	    {
+	      printf ("    Address Range: ");
+
+	      union
+	      {
+		Elf64_Addr a64[2];
+		Elf32_Addr a32[2];
+	      } addrs;
+
+	      size_t addr_size = gelf_fsize (ebl->elf, ELF_T_ADDR,
+					     2, EV_CURRENT);
+	      if (descsz != addr_size)
+		printf ("<unknown data>\n");
+	      else
+		{
+		  Elf_Data src =
+		    {
+		     .d_type = ELF_T_ADDR, .d_version = EV_CURRENT,
+		     .d_buf = (void *) desc, .d_size = descsz
+		    };
+
+		  Elf_Data dst =
+		    {
+		     .d_type = ELF_T_ADDR, .d_version = EV_CURRENT,
+		     .d_buf = &addrs, .d_size = descsz
+		    };
+
+		  if (gelf_xlatetom (ebl->elf, &dst, &src,
+				     elf_getident (ebl->elf,
+						   NULL)[EI_DATA]) == NULL)
+		    printf ("%s\n", elf_errmsg (-1));
+		  else
+		    {
+		      if (addr_size == 4)
+			printf ("%#" PRIx32 " - %#" PRIx32 "\n",
+				addrs.a32[0], addrs.a32[1]);
+		      else
+			printf ("%#" PRIx64 " - %#" PRIx64 "\n",
+				addrs.a64[0], addrs.a64[1]);
+		    }
+		}
+	    }
+
+	  /* Most data actually is inside the name.
+	     https://fedoraproject.org/wiki/Toolchain/Watermark  */
+
+	  /* We need at least 2 chars of data to describe the
+	     attribute and value encodings.  */
+	  const char *data = (name
+			      + strlen (ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX));
+	  if (namesz < 2)
+	    {
+	      printf ("<insufficient data>\n");
+	      return;
+	    }
+
+	  printf ("    ");
+
+	  /* In most cases the value comes right after the encoding bytes.  */
+	  const char *value = &data[2];
+	  switch (data[1])
+	    {
+	    case GNU_BUILD_ATTRIBUTE_VERSION:
+	      printf ("VERSION: ");
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_STACK_PROT:
+	      printf ("STACK_PROT: ");
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_RELRO:
+	      printf ("RELRO: ");
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_STACK_SIZE:
+	      printf ("STACK_SIZE: ");
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_TOOL:
+	      printf ("TOOL: ");
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_ABI:
+	      printf ("ABI: ");
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_PIC:
+	      printf ("PIC: ");
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_SHORT_ENUM:
+	      printf ("SHORT_ENUM: ");
+	      break;
+	    case 32 ... 126:
+	      printf ("\"%s\": ", &data[1]);
+	      value += strlen (&data[1]) + 1;
+	      break;
+	    default:
+	      printf ("<unknown>: ");
+	      break;
+	    }
+
+	  switch (data[0])
+	    {
+	    case GNU_BUILD_ATTRIBUTE_TYPE_NUMERIC:
+	      {
+		/* Any numbers are always in (unsigned) little endian.  */
+		static const Dwarf dbg
+		  = { .other_byte_order = MY_ELFDATA != ELFDATA2LSB };
+		size_t bytes = namesz - (value - name);
+		uint64_t val;
+		if (bytes == 1)
+		  val = *(unsigned char *) value;
+		else if (bytes == 2)
+		  val = read_2ubyte_unaligned (&dbg, value);
+		else if (bytes == 4)
+		  val = read_4ubyte_unaligned (&dbg, value);
+		else if (bytes == 8)
+		  val = read_8ubyte_unaligned (&dbg, value);
+		else
+		  goto unknown;
+		printf ("%" PRIx64, val);
+	      }
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_TYPE_STRING:
+	      printf ("\"%s\"", value);
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_TYPE_BOOL_TRUE:
+	      printf ("TRUE");
+	      break;
+	    case GNU_BUILD_ATTRIBUTE_TYPE_BOOL_FALSE:
+	      printf ("FALSE");
+	      break;
+	    default:
+	      {
+	      unknown:
+		printf ("<unknown>");
+	      }
+	      break;
+	    }
+
+	  printf ("\n");
+
+	  return;
+	}
+
       /* NT_VERSION doesn't have any info.  All data is in the name.  */
       if (descsz == 0 && type == NT_VERSION)
 	return;
diff --git a/libebl/eblobjnotetypename.c b/libebl/eblobjnotetypename.c
index 8cdd781..29a5391 100644
--- a/libebl/eblobjnotetypename.c
+++ b/libebl/eblobjnotetypename.c
@@ -1,5 +1,5 @@
 /* Return note type name.
-   Copyright (C) 2002, 2007, 2009, 2011, 2016 Red Hat, Inc.
+   Copyright (C) 2002, 2007, 2009, 2011, 2016, 2018 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <drepper@redhat.com>, 2002.
 
@@ -79,6 +79,29 @@ ebl_object_note_type_name (Ebl *ebl, const char *name, uint32_t type,
 	    }
 	}
 
+      if (strncmp (name, ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX,
+		   strlen (ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX)) == 0)
+	{
+	  /* GNU Build Attribute notes (ab)use the owner name to store
+	     most of their data.  Don't decode everything here.  Just
+	     the type.*/
+	  char *t = buf;
+	  const char *gba = "GNU Build Attribute";
+	  int w = snprintf (t, len, "%s ", gba);
+	  t += w;
+	  len -= w;
+	  if (type == NT_GNU_BUILD_ATTRIBUTE_OPEN)
+	    w = snprintf (t, len, "OPEN");
+	  else if (type == NT_GNU_BUILD_ATTRIBUTE_FUNC)
+	    w = snprintf (t, len, "FUNC");
+	  else
+	    w = snprintf (t, len, "%x", type);
+	  t += w;
+	  len -= w;
+
+	  return buf;
+	}
+
       if (strcmp (name, "GNU") != 0)
 	{
 	  /* NT_VERSION is special, all data is in the name.  */
diff --git a/libebl/libebl.h b/libebl/libebl.h
index 5830654..ca9b9fe 100644
--- a/libebl/libebl.h
+++ b/libebl/libebl.h
@@ -179,8 +179,8 @@ extern const char *ebl_object_note_type_name (Ebl *ebl, const char *name,
 					      char *buf, size_t len);
 
 /* Print information about object note if available.  */
-extern void ebl_object_note (Ebl *ebl, const char *name, uint32_t type,
-			     uint32_t descsz, const char *desc);
+extern void ebl_object_note (Ebl *ebl, uint32_t namesz, const char *name,
+			     uint32_t type, uint32_t descsz, const char *desc);
 
 /* Check whether an attribute in a .gnu_attributes section is recognized.
    Fills in *TAG_NAME with the name for this tag.
diff --git a/libelf/ChangeLog b/libelf/ChangeLog
index 53da9a6..2675ba5 100644
--- a/libelf/ChangeLog
+++ b/libelf/ChangeLog
@@ -1,3 +1,12 @@
+2018-11-12  Mark Wielaard  <mark@klomp.org>
+
+	* elf-knowledge.c (ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX): New define.
+	(NT_GNU_BUILD_ATTRIBUTE_{OPEN,FUNC}): Likewise.
+	(GNU_BUILD_ATTRIBUTE_TYPE_{NUMERIC,STRING,BOOL_TRUE,BOOL_FALSE}):
+	Likewise.
+	(GNU_BUILD_ATTRIBUTE_{VERSION,STACK_PROT,RELRO,STACK_SIZE,TOOL,ABI,
+	PIC,SHORT_ENUM}): Likewise.
+
 2018-11-09  Mark Wielaard  <mark@klomp.org>
 
 	* elf_compress.c (__libelf_reset_rawdata): Make rawdata change
diff --git a/libelf/elf-knowledge.h b/libelf/elf-knowledge.h
index 64f5887..9d3be0f 100644
--- a/libelf/elf-knowledge.h
+++ b/libelf/elf-knowledge.h
@@ -77,4 +77,25 @@
    || ((Ehdr)->e_machine == EM_S390					      \
        && (Ehdr)->e_ident[EI_CLASS] == ELFCLASS64) ? 8 : 4)
 
+/* GNU Annobin notes are not fully standardized and abuses the owner name.  */
+
+#define ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX "GA"
+
+#define NT_GNU_BUILD_ATTRIBUTE_OPEN 0x100
+#define NT_GNU_BUILD_ATTRIBUTE_FUNC 0x101
+
+#define GNU_BUILD_ATTRIBUTE_TYPE_NUMERIC	'*'
+#define GNU_BUILD_ATTRIBUTE_TYPE_STRING		'$'
+#define GNU_BUILD_ATTRIBUTE_TYPE_BOOL_TRUE	'+'
+#define GNU_BUILD_ATTRIBUTE_TYPE_BOOL_FALSE	'!'
+
+#define GNU_BUILD_ATTRIBUTE_VERSION	1
+#define GNU_BUILD_ATTRIBUTE_STACK_PROT	2
+#define GNU_BUILD_ATTRIBUTE_RELRO	3
+#define GNU_BUILD_ATTRIBUTE_STACK_SIZE	4
+#define GNU_BUILD_ATTRIBUTE_TOOL	5
+#define GNU_BUILD_ATTRIBUTE_ABI		6
+#define GNU_BUILD_ATTRIBUTE_PIC		7
+#define GNU_BUILD_ATTRIBUTE_SHORT_ENUM	8
+
 #endif	/* elf-knowledge.h */
diff --git a/src/ChangeLog b/src/ChangeLog
index 9f26b25..8acf13c 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2018-11-12  Mark Wielaard  <mark@klomp.org>
+
+	* elflint.c (check_note_data): Recognize NT_GNU_BUILD_ATTRIBUTE_OPEN
+	and NT_GNU_BUILD_ATTRIBUTE_OPEN.
+	* readelf.c (handle_notes_data): Handle
+	ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX. Pass nhdr.n_namesz to
+	ebl_object_note.
+
 2018-11-11  Mark Wielaard  <mark@klomp.org>
 
 	* readelf.c (handle_notes_data): Pass n_descsz to
diff --git a/src/elflint.c b/src/elflint.c
index bddb8dd..810c8bd 100644
--- a/src/elflint.c
+++ b/src/elflint.c
@@ -4344,6 +4344,19 @@ section [%2d] '%s': unknown core file note type %" PRIu32
 	      }
 	      goto unknown_note;
 
+	  case NT_GNU_BUILD_ATTRIBUTE_OPEN:
+	  case NT_GNU_BUILD_ATTRIBUTE_FUNC:
+	    /* GNU Build Attributes store most data in the owner
+	       name, which must start with the
+	       ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX "GA".  */
+	    if (nhdr.n_namesz >= sizeof ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX
+		&& strncmp (data->d_buf + name_offset,
+			    ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX,
+			    strlen (ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX)) == 0)
+	      break;
+	    else
+	      goto unknown_note;
+
 	  case 0:
 	    /* Linux vDSOs use a type 0 note for the kernel version word.  */
 	    if (nhdr.n_namesz == sizeof "Linux"
diff --git a/src/readelf.c b/src/readelf.c
index 659e34f..3a73710 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -12193,10 +12193,21 @@ handle_notes_data (Ebl *ebl, const GElf_Ehdr *ehdr,
       const char *name = nhdr.n_namesz == 0 ? "" : data->d_buf + name_offset;
       const char *desc = data->d_buf + desc_offset;
 
+      /* GNU Build Attributes are weird, they store most of their data
+	 into the owner name field.  Extract just the owner name
+	 prefix here, then use the rest later as data.  */
+      bool is_gnu_build_attr
+	= strncmp (name, ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX,
+		   strlen (ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX)) == 0;
+      const char *print_name = (is_gnu_build_attr
+				? ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX : name);
+      size_t print_namesz = (is_gnu_build_attr
+			     ? strlen (print_name) : nhdr.n_namesz);
+
       char buf[100];
       char buf2[100];
       printf (gettext ("  %-13.*s  %9" PRId32 "  %s\n"),
-	      (int) nhdr.n_namesz, name, nhdr.n_descsz,
+	      (int) print_namesz, print_name, nhdr.n_descsz,
 	      ehdr->e_type == ET_CORE
 	      ? ebl_core_note_type_name (ebl, nhdr.n_type,
 					 buf, sizeof (buf))
@@ -12237,7 +12248,8 @@ handle_notes_data (Ebl *ebl, const GElf_Ehdr *ehdr,
 		handle_core_note (ebl, &nhdr, name, desc);
 	    }
 	  else
-	    ebl_object_note (ebl, name, nhdr.n_type, nhdr.n_descsz, desc);
+	    ebl_object_note (ebl, nhdr.n_namesz, name, nhdr.n_type,
+			     nhdr.n_descsz, desc);
 	}
     }
 
diff --git a/tests/ChangeLog b/tests/ChangeLog
index d92b8e3..e6a9bde 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,3 +1,7 @@
+2018-11-12  Mark Wielaard  <mark@klomp.org>
+
+	* run-readelf-n.sh: Add testfile-annobingroup.o test.
+
 2018-11-11  Mark Wielaard  <mark@klomp.org>
 
 	* run-readelf-n.sh: Fix NT_GNU_ABI_TAG type. Add testfile11 test
diff --git a/tests/run-readelf-n.sh b/tests/run-readelf-n.sh
index 7e2a845..c2db2ce 100755
--- a/tests/run-readelf-n.sh
+++ b/tests/run-readelf-n.sh
@@ -70,3 +70,58 @@ Note section [35] '.note' of 60 bytes at offset 0x13364:
   01.01                  0  VERSION
   01.01                  0  VERSION
 EOF
+
+# See run-annobingroup.sh
+testfiles testfile-annobingroup.o
+testrun_compare ${abs_top_builddir}/src/readelf -n testfile-annobingroup.o << EOF
+
+Note section [ 5] '.gnu.build.attributes' of 272 bytes at offset 0x50:
+  Owner          Data size  Type
+  GA                    16  GNU Build Attribute OPEN
+    Address Range: 0 - 0
+    VERSION: "3p8"
+  GA                     0  GNU Build Attribute OPEN
+    TOOL: "gcc 8.1.1 20180712"
+  GA                     0  GNU Build Attribute OPEN
+    "GOW": 5
+  GA                     0  GNU Build Attribute OPEN
+    STACK_PROT: 0
+  GA                     0  GNU Build Attribute OPEN
+    "stack_clash": FALSE
+  GA                     0  GNU Build Attribute OPEN
+    "cf_protection": 0
+  GA                     0  GNU Build Attribute OPEN
+    PIC: 0
+  GA                     0  GNU Build Attribute OPEN
+    SHORT_ENUM: FALSE
+  GA                     0  GNU Build Attribute OPEN
+    ABI: c001100000012
+  GA                     0  GNU Build Attribute OPEN
+    "stack_realign": FALSE
+
+Note section [ 7] '.gnu.build.attributes..text.unlikely' of 216 bytes at offset 0x160:
+  Owner          Data size  Type
+  GA                    16  GNU Build Attribute FUNC
+    Address Range: 0 - 0
+    ABI: c001100000012
+  GA                     0  GNU Build Attribute FUNC
+    "stack_realign": FALSE
+  GA                     0  GNU Build Attribute FUNC
+    STACK_PROT: 0
+  GA                     0  GNU Build Attribute FUNC
+    "stack_clash": FALSE
+  GA                     0  GNU Build Attribute FUNC
+    "cf_protection": 0
+  GA                     0  GNU Build Attribute FUNC
+    PIC: 0
+  GA                     0  GNU Build Attribute FUNC
+    "GOW": 5
+  GA                     0  GNU Build Attribute FUNC
+    SHORT_ENUM: FALSE
+
+Note section [22] '.note.gnu.property' of 48 bytes at offset 0x40c:
+  Owner          Data size  Type
+  GNU                   32  GNU_PROPERTY_TYPE_0
+    X86 0xc0000000 data: 00 00 00 00
+    X86 0xc0000001 data: 00 00 00 00
+EOF
-- 
1.8.3.1



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