x86: Check IFUNC definition in unrelocated executable [BZ #20019]

Calling an IFUNC function defined in unrelocated executable also leads to
segfault.  Issue a fatal error message when calling IFUNC function defined
in the unrelocated executable from a shared library.

On x86, ifuncmain6pie failed with:

[hjl@gnu-cfl-2 build-i686-linux]$ ./elf/ifuncmain6pie --direct
./elf/ifuncmain6pie: IFUNC symbol 'foo' referenced in '/export/build/gnu/tools-build/glibc-32bit/build-i686-linux/elf/ifuncmod6.so' is defined in the executable and creates an unsatisfiable circular dependency.
[hjl@gnu-cfl-2 build-i686-linux]$ readelf -rW elf/ifuncmod6.so | grep foo
00003ff4  00000706 R_386_GLOB_DAT         0000400c   foo_ptr
00003ff8  00000406 R_386_GLOB_DAT         00000000   foo
0000400c  00000401 R_386_32               00000000   foo
[hjl@gnu-cfl-2 build-i686-linux]$

Remove non-JUMP_SLOT relocations against foo in ifuncmod6.so, which
trigger the circular IFUNC dependency, and build ifuncmain6pie with
-Wl,-z,lazy.

(cherry picked from commits 6ea5b57afa
 and 7137d682eb)

NEWS

@@ -35,6 +35,7 @@ The following bugs are resolved with this release:
   [18035] Fix pldd hang
   [19444] build failures with -O1 due to -Wmaybe-uninitialized
   [20018] getaddrinfo should reject IP addresses with trailing characters
+  [20019] NULL pointer dereference in libc.so.6 IFUNC due to uninitialized GOT
   [20209] localedata: Spelling mistake for Sunday in Greenlandic kl_GL
   [20568] Fix crash in _IO_wfile_sync
   [22927] libanl: properly cleanup if first helper thread creation failed

elf/Makefile

@@ -1267,6 +1267,8 @@ CFLAGS-ifuncmain5pie.c += $(pie-ccflag)
 CFLAGS-ifuncmain6pie.c += $(pie-ccflag)
 CFLAGS-ifuncmain7pie.c += $(pie-ccflag)
 
+LDFLAGS-ifuncmain6pie = -Wl,-z,lazy
+
 $(objpfx)ifuncmain1pie: $(objpfx)ifuncmod1.so
 $(objpfx)ifuncmain1staticpie: $(objpfx)ifuncdep1pic.o
 $(objpfx)ifuncmain1vispie: $(objpfx)ifuncmod1.so

elf/ifuncmain6pie.c

@@ -9,7 +9,6 @@
 #include "ifunc-sel.h"
 
 typedef int (*foo_p) (void);
-extern foo_p foo_ptr;
 
 static int
 one (void)
@@ -28,20 +27,17 @@ foo_ifunc (void)
 }
 
 extern int foo (void);
-extern foo_p get_foo (void);
+extern int call_foo (void);
 extern foo_p get_foo_p (void);
 
-foo_p my_foo_ptr = foo;
+foo_p foo_ptr = foo;
 
 int
 main (void)
 {
   foo_p p;
 
-  p = get_foo ();
-  if (p != foo)
-    abort ();
-  if ((*p) () != -30)
+  if (call_foo () != -30)
     abort ();
 
   p = get_foo_p ();
@@ -52,12 +48,8 @@ main (void)
 
   if (foo_ptr != foo)
     abort ();
-  if (my_foo_ptr != foo)
-    abort ();
   if ((*foo_ptr) () != -30)
     abort ();
-  if ((*my_foo_ptr) () != -30)
-    abort ();
   if (foo () != -30)
     abort ();
 

elf/ifuncmod6.c

@@ -4,7 +4,7 @@ extern int foo (void);
 
 typedef int (*foo_p) (void);
 
-foo_p foo_ptr = foo;
+extern foo_p foo_ptr;
 
 foo_p
 get_foo_p (void)
@@ -12,8 +12,8 @@ get_foo_p (void)
   return foo_ptr;
 }
 
-foo_p
-get_foo (void)
+int
+call_foo (void)
 {
-  return foo;
+  return foo ();
 }

sysdeps/i386/dl-machine.h

@@ -338,16 +338,22 @@ elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
 	{
 # ifndef RTLD_BOOTSTRAP
 	  if (sym_map != map
-	      && sym_map->l_type != lt_executable
 	      && !sym_map->l_relocated)
 	    {
 	      const char *strtab
 		= (const char *) D_PTR (map, l_info[DT_STRTAB]);
-	      _dl_error_printf ("\
+	      if (sym_map->l_type == lt_executable)
+		_dl_fatal_printf ("\
+%s: IFUNC symbol '%s' referenced in '%s' is defined in the executable \
+and creates an unsatisfiable circular dependency.\n",
+				  RTLD_PROGNAME, strtab + refsym->st_name,
+				  map->l_name);
+	      else
+		_dl_error_printf ("\
 %s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
-				RTLD_PROGNAME, map->l_name,
-				sym_map->l_name,
-				strtab + refsym->st_name);
+				  RTLD_PROGNAME, map->l_name,
+				  sym_map->l_name,
+				  strtab + refsym->st_name);
 	    }
 # endif
 	  value = ((Elf32_Addr (*) (void)) value) ();

sysdeps/x86_64/dl-machine.h

@@ -315,16 +315,22 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
 	{
 # ifndef RTLD_BOOTSTRAP
 	  if (sym_map != map
-	      && sym_map->l_type != lt_executable
 	      && !sym_map->l_relocated)
 	    {
 	      const char *strtab
 		= (const char *) D_PTR (map, l_info[DT_STRTAB]);
-	      _dl_error_printf ("\
+	      if (sym_map->l_type == lt_executable)
+		_dl_fatal_printf ("\
+%s: IFUNC symbol '%s' referenced in '%s' is defined in the executable \
+and creates an unsatisfiable circular dependency.\n",
+				  RTLD_PROGNAME, strtab + refsym->st_name,
+				  map->l_name);
+	      else
+		_dl_error_printf ("\
 %s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
-				RTLD_PROGNAME, map->l_name,
-				sym_map->l_name,
-				strtab + refsym->st_name);
+				  RTLD_PROGNAME, map->l_name,
+				  sym_map->l_name,
+				  strtab + refsym->st_name);
 	    }
 # endif
 	  value = ((ElfW(Addr) (*) (void)) value) ();