[PATCH] ld/elf: Don't take IFUNC address in the shared object

[H.J. Lu]

On Sat, Jan 16, 2021 at 6:53 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On x86, glibc 2.33 starts to issue a fatal error message when calling
> IFUNC function defined in the unrelocated executable from a shared
> library.
>
> 1. Update x86 ELF linker to always convert IFUNC function defined in
> position-dependent executable (PDE) to the normal function.  GOT in PDE
> will be updated by R_*_IRELATIVE at run-time.
> 2. Update PR ld/23169 tests not to compare function address of external
> IFUNC function in the shared object to avoid calling the IFUNC function
> defined in the unrelocated executable.
>
> bfd/
>
>         PR ld/23169
>         * elfxx-x86.c (_bfd_x86_elf_link_fixup_ifunc_symbol): Don't
>         check pointer_equality_needed.
>
> ld/
>
>         PR ld/23169
>         * testsuite/ld-ifunc/ifunc.exp: Replace pr23169c.rd with
>         pr23169a.rd for pr23169c and pr23169f.  Remove pr23169e tests.
>         * testsuite/ld-ifunc/pr23169a.c: Don't take function address.
> ---
>  bfd/elfxx-x86.c                  |  3 +--
>  ld/testsuite/ld-ifunc/ifunc.exp  | 22 ++--------------------
>  ld/testsuite/ld-ifunc/pr23169a.c |  2 +-
>  3 files changed, 4 insertions(+), 23 deletions(-)
>
> diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
> index 8cda8d2d97c..93ad38c5eb0 100644
> --- a/bfd/elfxx-x86.c
> +++ b/bfd/elfxx-x86.c
> @@ -1711,8 +1711,7 @@ _bfd_x86_elf_link_fixup_ifunc_symbol (struct bfd_link_info *info,
>        && h->def_regular
>        && h->dynindx != -1
>        && h->plt.offset != (bfd_vma) -1
> -      && h->type == STT_GNU_IFUNC
> -      && h->pointer_equality_needed)
> +      && h->type == STT_GNU_IFUNC)
>      {
>        asection *plt_s;
>        bfd_vma plt_offset;
> diff --git a/ld/testsuite/ld-ifunc/ifunc.exp b/ld/testsuite/ld-ifunc/ifunc.exp
> index 31666d0f29c..9d3ace65216 100644
> --- a/ld/testsuite/ld-ifunc/ifunc.exp
> +++ b/ld/testsuite/ld-ifunc/ifunc.exp
> @@ -640,7 +640,7 @@ run_cc_link_tests [list \
>         "$NOPIE_LDFLAGS -Wl,--no-as-needed tmpdir/libpr23169a.so" \
>         "-fPIE -O2 -g" \
>         { pr23169b.c pr23169c.c } \
> -       {{readelf {--dyn-syms} pr23169c.rd} \
> +       {{readelf {--dyn-syms} pr23169a.rd} \
>          {readelf {-r -W} pr23169b.rd}} \
>         "pr23169c" \
>      ] \
> @@ -653,21 +653,12 @@ run_cc_link_tests [list \
>          {readelf {-r -W} pr23169b.rd}} \
>         "pr23169d" \
>      ] \
> -    [list \
> -       "Build pr23169e" \
> -       "-pie -Wl,--no-as-needed,-z,now tmpdir/libpr23169b.so" \
> -       "-fPIE -O2 -g" \
> -       { pr23169b.c pr23169c.c } \
> -       {{readelf {--dyn-syms} pr23169c.rd} \
> -        {readelf {-r -W} pr23169b.rd}} \
> -       "pr23169e" \
> -    ] \
>      [list \
>         "Build pr23169f" \
>         "$NOPIE_LDFLAGS -Wl,--no-as-needed,-z,now tmpdir/libpr23169b.so" \
>         "-fPIE -O2 -g" \
>         { pr23169b.c pr23169c.c } \
> -       {{readelf {--dyn-syms} pr23169c.rd} \
> +       {{readelf {--dyn-syms} pr23169a.rd} \
>          {readelf {-r -W} pr23169b.rd}} \
>         "pr23169f" \
>      ] \
> @@ -774,15 +765,6 @@ run_ld_link_exec_tests [list \
>         "pass.out" \
>         "$NOPIE_CFLAGS -O2 -g" \
>      ] \
> -    [list \
> -       "Run pr23169e" \
> -       "-pie -Wl,--no-as-needed,-z,now tmpdir/libpr23169b.so" \
> -       "" \
> -       { pr23169b.c pr23169c.c } \
> -       "pr23169e" \
> -       "pass.out" \
> -       "-fPIE -O2 -g" \
> -    ] \
>      [list \
>         "Run pr23169f" \
>         "$NOPIE_LDFLAGS -Wl,--no-as-needed,-z,now tmpdir/libpr23169b.so" \
> diff --git a/ld/testsuite/ld-ifunc/pr23169a.c b/ld/testsuite/ld-ifunc/pr23169a.c
> index 02bf2208904..8beed283bc8 100644
> --- a/ld/testsuite/ld-ifunc/pr23169a.c
> +++ b/ld/testsuite/ld-ifunc/pr23169a.c
> @@ -4,6 +4,6 @@ extern int func (void);
>  void
>  foo (void)
>  {
> -  if (func_p != &func || func_p () != 0xbadbeef)
> +  if (func () != 0xbadbeef || func_p () != 0xbadbeef)
>      __builtin_abort ();
>  }
> --
> 2.29.2
>

Hi Nick,

Some tests in binutils 2.36 will fail on Linux/x86 with glibc 2.33 or Fedora 33
with glibc-2.32-3 due to

commit 6ea5b57afa5cdc9ce367d2b69a2cebfb273e4617
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Mon Dec 28 05:28:49 2020 -0800

    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.

OK to backport this patch to 2.36?

Thanks.

-- 
H.J.