rtld: Clean up PT_NOTE and add PT_GNU_PROPERTY handling

Add generic code to handle PT_GNU_PROPERTY notes. Invalid
content is ignored, _dl_process_pt_gnu_property is always called
after PT_LOAD segments are mapped and it has no failure modes.
Currently only one NT_GNU_PROPERTY_TYPE_0 note is handled, which
contains target specific properties: the _dl_process_gnu_property
hook is called for each property.

The old _dl_process_pt_note and _rtld_process_pt_note differ in how
the program header is read.  The old _dl_process_pt_note is called
before PT_LOAD segments are mapped and _rtld_process_pt_note is called
after PT_LOAD segments are mapped. The old _rtld_process_pt_note is
removed and _dl_process_pt_note is always called after PT_LOAD
segments are mapped and now it has no failure modes.

The program headers are scanned backwards so that PT_NOTE can be
skipped if PT_GNU_PROPERTY exists.

Co-Authored-By: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

2 files changed, 96 insertions, 12 deletions

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 06f2ba7264..e39980fb19 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -853,6 +853,77 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
 }
 
 
+/* Process PT_GNU_PROPERTY program header PH in module L after
+   PT_LOAD segments are mapped.  Only one NT_GNU_PROPERTY_TYPE_0
+   note is handled which contains processor specific properties.  */
+
+void
+_dl_process_pt_gnu_property (struct link_map *l, const ElfW(Phdr) *ph)
+{
+  const ElfW(Nhdr) *note = (const void *) (ph->p_vaddr + l->l_addr);
+  const ElfW(Addr) size = ph->p_memsz;
+  const ElfW(Addr) align = ph->p_align;
+
+  /* The NT_GNU_PROPERTY_TYPE_0 note must be aligned to 4 bytes in
+     32-bit objects and to 8 bytes in 64-bit objects.  Skip notes
+     with incorrect alignment.  */
+  if (align != (__ELF_NATIVE_CLASS / 8))
+    return;
+
+  const ElfW(Addr) start = (ElfW(Addr)) note;
+  unsigned int last_type = 0;
+
+  while ((ElfW(Addr)) (note + 1) - start < size)
+    {
+      /* Find the NT_GNU_PROPERTY_TYPE_0 note.  */
+      if (note->n_namesz == 4
+	  && note->n_type == NT_GNU_PROPERTY_TYPE_0
+	  && memcmp (note + 1, "GNU", 4) == 0)
+	{
+	  /* Check for invalid property.  */
+	  if (note->n_descsz < 8
+	      || (note->n_descsz % sizeof (ElfW(Addr))) != 0)
+	    return;
+
+	  /* Start and end of property array.  */
+	  unsigned char *ptr = (unsigned char *) (note + 1) + 4;
+	  unsigned char *ptr_end = ptr + note->n_descsz;
+
+	  do
+	    {
+	      unsigned int type = *(unsigned int *) ptr;
+	      unsigned int datasz = *(unsigned int *) (ptr + 4);
+
+	      /* Property type must be in ascending order.  */
+	      if (type < last_type)
+		return;
+
+	      ptr += 8;
+	      if ((ptr + datasz) > ptr_end)
+		return;
+
+	      last_type = type;
+
+	      /* Target specific property processing.  */
+	      if (_dl_process_gnu_property (l, type, datasz, ptr) == 0)
+		return;
+
+	      /* Check the next property item.  */
+	      ptr += ALIGN_UP (datasz, sizeof (ElfW(Addr)));
+	    }
+	  while ((ptr_end - ptr) >= 8);
+
+	  /* Only handle one NT_GNU_PROPERTY_TYPE_0.  */
+	  return;
+	}
+
+      note = ((const void *) note
+	      + ELF_NOTE_NEXT_OFFSET (note->n_namesz, note->n_descsz,
+				      align));
+    }
+}
+
+
 /* Map in the shared object NAME, actually located in REALNAME, and already
    opened on FD.  */
 
@@ -1145,14 +1216,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	  l->l_relro_addr = ph->p_vaddr;
 	  l->l_relro_size = ph->p_memsz;
 	  break;
-
-	case PT_NOTE:
-	  if (_dl_process_pt_note (l, ph, fd, fbp))
-	    {
-	      errstring = N_("cannot process note segment");
-	      goto call_lose;
-	    }
-	  break;
 	}
 
     if (__glibc_unlikely (nloadcmds == 0))
@@ -1188,6 +1251,21 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 				  maplength, has_holes, loader);
     if (__glibc_unlikely (errstring != NULL))
       goto call_lose;
+
+    /* Process program headers again after load segments are mapped in
+       case processing requires accessing those segments.  Scan program
+       headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
+       exits.  */
+    for (ph = &phdr[l->l_phnum]; ph != phdr; --ph)
+      switch (ph[-1].p_type)
+	{
+	case PT_NOTE:
+	  _dl_process_pt_note (l, &ph[-1]);
+	  break;
+	case PT_GNU_PROPERTY:
+	  _dl_process_pt_gnu_property (l, &ph[-1]);
+	  break;
+	}
   }
 
   if (l->l_ld == 0)
diff --git a/elf/rtld.c b/elf/rtld.c
index 882b070cc0..f4c2602d65 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -1507,11 +1507,17 @@ of this helper program; chances are you did not intend to run this program.\n\
 	main_map->l_relro_addr = ph->p_vaddr;
 	main_map->l_relro_size = ph->p_memsz;
 	break;
-
+      }
+  /* Process program headers again, but scan them backwards so
+     that PT_NOTE can be skipped if PT_GNU_PROPERTY exits.  */
+  for (ph = &phdr[phnum]; ph != phdr; --ph)
+    switch (ph[-1].p_type)
+      {
       case PT_NOTE:
-	if (_rtld_process_pt_note (main_map, ph))
-	  _dl_error_printf ("\
-ERROR: '%s': cannot process note segment.\n", _dl_argv[0]);
+	_dl_process_pt_note (main_map, &ph[-1]);
+	break;
+      case PT_GNU_PROPERTY:
+	_dl_process_pt_gnu_property (main_map, &ph[-1]);
 	break;
       }