[PATCH v5 07/14] rtld: Handle PT_GNU_PROPERTY

[H.J. Lu]

On Mon, Jun 22, 2020 at 7:04 AM Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
>
> Add generic code to handle PT_GNU_PROPERTY notes. Unlike
> _dl_process_pt_note, _dl_process_pt_gnu_property is generic,
> has no failure mode (invalid content is ignored) and always
> called after PT_LOAD segments are mapped. Currently only one
> NT_GNU_PROPERTY_TYPE_0 note is handled, which contains target
> specific properties: the _dl_process_gnu_property target hook
> is called for each property.
>
> Otherwise it follows the existing x86 note processing logic.
> ---
>  elf/dl-load.c              | 81 ++++++++++++++++++++++++++++++++++++++
>  elf/rtld.c                 |  4 ++
>  sysdeps/generic/dl-prop.h  | 19 ++++++---
>  sysdeps/generic/ldsodefs.h |  4 ++
>  sysdeps/x86/dl-prop.h      |  7 ++++
>  5 files changed, 110 insertions(+), 5 deletions(-)
>
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 06f2ba7264..66bd0ca0a3 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.  */
>
> @@ -1188,6 +1259,16 @@ _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.  */
> +    for (ph = phdr; ph < &phdr[l->l_phnum]; ++ph)
> +      switch (ph->p_type)
> +       {
> +       case PT_GNU_PROPERTY:
> +         _dl_process_pt_gnu_property (l, ph);
> +         break;
> +       }
>    }
>

This patch is immediately changed by the next patch.  You should
combine them into
one patch and add

Co-Authored-By: H.J. Lu <hjl.tools@gmail.com>

Thanks.

-- 
H.J.