Re: Create a hook for inspecting program headers during library load

[Will Newton <will dot newton at linaro dot org>]

On 2 October 2014 16:02, Matthew Fortune <Matthew.Fortune@imgtec.com> wrote:
> Patch updated below. Though I did remember Joseph steering me away from
> an ifdef based interface while reworking this:
>
> https://sourceware.org/ml/libc-alpha/2014-05/msg00045.html
>
> Does this seem more appropriate?

You could implement it using the sysdeps mechanism, e.g. see how
dl-irel.h and similar headers operate.

> Tested for x86_64-linux-gnu.
>
> Thanks,
> Matthew
>
>         * elf/dl-load.c (dl-load-stubs.h): Include.
>         (open_verify): Add hook for phdr check.
>         * elf/dl-load-stubs.h: New file.
> ---
>  elf/dl-load-stubs.h | 32 ++++++++++++++++++++++++++++++++
>  elf/dl-load.c       |  6 ++++++
>  2 files changed, 38 insertions(+)
>  create mode 100644 elf/dl-load-stubs.h
>
> diff --git a/elf/dl-load-stubs.h b/elf/dl-load-stubs.h
> new file mode 100644
> index 0000000..8eb671d
> --- /dev/null
> +++ b/elf/dl-load-stubs.h
> @@ -0,0 +1,32 @@
> +/* Stub implementations for loader functions.
> +   Copyright (C) 2014 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +/* Provide a default implementation of elf_machine_reject_phdr_p if a port
> +   has not provided its own.  */
> +
> +#ifndef ELF_MACHINE_REJECT_PHDR_P
> +/* Return true iff ELF program headers are incompatible with the running
> +   host.  */
> +static inline bool
> +elf_machine_reject_phdr_p (const ElfW(Phdr) *phdr, uint_fast16_t phnum,
> +                          const char *buf, size_t len, int fd,
> +                          struct link_map *map)
> +{
> +  return false;
> +}
> +#endif
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 016a99c..aff3506 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -31,6 +31,7 @@
>  #include <sys/stat.h>
>  #include <sys/types.h>
>  #include "dynamic-link.h"
> +#include "dl-load-stubs.h"
>  #include <abi-tag.h>
>  #include <stackinfo.h>
>  #include <caller.h>
> @@ -1697,6 +1698,11 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader,
>             }
>         }
>
> +      if (__glibc_unlikely (
> +            elf_machine_reject_phdr_p (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
> +                                       fd, loader)))
> +       goto close_and_out;
> +
>        /* Check .note.ABI-tag if present.  */
>        for (ph = phdr; ph < &phdr[ehdr->e_phnum]; ++ph)
>         if (ph->p_type == PT_NOTE && ph->p_filesz >= 32 && ph->p_align >= 4)
> --
> 1.9.4



-- 
Will Newton
Toolchain Working Group, Linaro