Re: PING: [PATCH] aarch64: Disallow copy relocations on protected data

[Fangrui Song <i@maskray.me>]

On 2022-05-31, Fangrui Song wrote:
>On Fri, May 27, 2022 at 3:43 PM Fangrui Song <i@maskray.me> wrote:
>>
>> On Mon, May 23, 2022 at 10:10 PM Fangrui Song <i@maskray.me> wrote:
>> >
>> > The behavior matches ld.lld which has been used on many aarch64 OSes.
>> >
>> > Rationale: copy relocations indicate that the executable and the shared object
>> > would access different copies, if the shared object does not reference the
>> > variable with GLOB_DAT.
>> >
>> > Note: x86 requires GNU_PROPERTY_NO_COPY_ON_PROTECTED to have the error.
>> > This is to largely due to GCC 5's
>> > "x86-64: Optimize access to globals in PIE with copy reloc" which started to use
>> > direct access relocations for external data symbols in -fpie mode.
>> >
>> > GCC's aarch64 port does not have the change. Nowadays with most builds switching
>> > to -fpie/-fpic, aarch64 mostly doesn't need to worry about copy relocations. So
>> > for aarch64 we simply don't check GNU_PROPERTY_NO_COPY_ON_PROTECTED.
>>
>> The diagnostic is requested on
>> https://sourceware.org/pipermail/libc-alpha/2022-May/139014.html
>>
>> > ---
>> >  bfd/elfnn-aarch64.c                           | 28 ++++++++++++++++++-
>> >  ld/testsuite/ld-aarch64/aarch64-elf.exp       |  9 ++++++
>> >  .../ld-aarch64/copy-reloc-protected.d         |  2 ++
>> >  ld/testsuite/ld-aarch64/protected.s           |  8 ++++++
>> >  4 files changed, 46 insertions(+), 1 deletion(-)
>> >  create mode 100644 ld/testsuite/ld-aarch64/copy-reloc-protected.d
>> >  create mode 100644 ld/testsuite/ld-aarch64/protected.s
>> >
>> > diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
>> > index 4926bab9cf2..8896b0f78dd 100644
>> > --- a/bfd/elfnn-aarch64.c
>> > +++ b/bfd/elfnn-aarch64.c
>> > @@ -2579,6 +2579,9 @@ struct elf_aarch64_link_hash_entry
>> >       this symbol.  */
>> >    unsigned int got_type;
>> >
>> > +  /* TRUE if symbol is defined as a protected symbol.  */
>> > +  unsigned int def_protected : 1;
>> > +
>> >    /* A pointer to the most recently used stub hash entry against this
>> >       symbol.  */
>> >    struct elf_aarch64_stub_hash_entry *stub_cache;
>> > @@ -2855,9 +2858,16 @@ elfNN_aarch64_copy_indirect_symbol (struct bfd_link_info *info,
>> >  static void
>> >  elfNN_aarch64_merge_symbol_attribute (struct elf_link_hash_entry *h,
>> >                                       unsigned int st_other,
>> > -                                     bool definition ATTRIBUTE_UNUSED,
>> > +                                     bool definition,
>> >                                       bool dynamic ATTRIBUTE_UNUSED)
>> >  {
>> > +  if (definition)
>> > +    {
>> > +      struct elf_aarch64_link_hash_entry *eh
>> > +       = (struct elf_aarch64_link_hash_entry *) h;
>> > +      eh->def_protected = ELF_ST_VISIBILITY (st_other) == STV_PROTECTED;
>> > +    }
>> > +
>> >    unsigned int isym_sto = st_other & ~ELF_ST_VISIBILITY (-1);
>> >    unsigned int h_sto = h->other & ~ELF_ST_VISIBILITY (-1);
>> >
>> > @@ -8701,6 +8711,22 @@ elfNN_aarch64_allocate_dynrelocs (struct elf_link_hash_entry *h, void *inf)
>> >    if (h->dyn_relocs == NULL)
>> >      return true;
>> >
>> > +  for (p = h->dyn_relocs; p != NULL; p = p->next)
>> > +    if (eh->def_protected)
>> > +      {
>> > +       /* Disallow copy relocations against protected symbol.  */
>> > +       asection *s = p->sec->output_section;
>> > +       if (s != NULL && (s->flags & SEC_READONLY) != 0)
>> > +         {
>> > +           info->callbacks->einfo
>> > +               /* xgettext:c-format */
>> > +               (_ ("%F%P: %pB: copy relocation against non-copyable "
>> > +                   "protected symbol `%s'\n"),
>> > +                p->sec->owner, h->root.root.string);
>> > +           return false;
>> > +         }
>> > +      }
>> > +
>> >    /* In the shared -Bsymbolic case, discard space allocated for
>> >       dynamic pc-relative relocs against symbols which turn out to be
>> >       defined in regular objects.  For the normal shared case, discard
>> > diff --git a/ld/testsuite/ld-aarch64/aarch64-elf.exp b/ld/testsuite/ld-aarch64/aarch64-elf.exp
>> > index 64476f111e0..31162277bd9 100644
>> > --- a/ld/testsuite/ld-aarch64/aarch64-elf.exp
>> > +++ b/ld/testsuite/ld-aarch64/aarch64-elf.exp
>> > @@ -407,6 +407,8 @@ set aarch64elflinktests {
>> >      {copy-reloc-exe-2.s} {{objdump -R copy-reloc-2.d}} "copy-reloc-2"}
>> >    {"ld-aarch64/exe with copy relocation elimination" "-e0 tmpdir/copy-reloc-so.so" "" ""
>> >      {copy-reloc-exe-eliminate.s} {{objdump -R copy-reloc-eliminate.d}} "copy-reloc-elimination"}
>> > +  {"Build .so with protected data" "-shared" "" "" {protected.s}
>> > +    {} "protected.so"}
>> >    {"ld-aarch64/so with global func" "-shared" "" "" {func-in-so.s}
>> >      {} "func-in-so.so"}
>> >    {"ld-aarch64/func sym hash opt for exe"
>> > @@ -416,8 +418,15 @@ set aarch64elflinktests {
>> >      {} "libbti-plt-so.so"}
>> >  }
>> >
>> > +set aarch64elfcclinktests [list \
>> > +  [list "copy relocation on protected data" \
>> > +    "-no-pie tmpdir/copy-reloc-exe.o tmpdir/protected.so" "" \
>> > +    {} {{error_output copy-reloc-protected.d}} "copy-reloc-protected"]
>> > +]
>> > +
>> >  if [check_shared_lib_support] {
>> >      run_ld_link_tests $aarch64elflinktests
>> > +    run_cc_link_tests $aarch64elfcclinktests
>> >  }
>> >
>> >  run_dump_test "bti-plt-3"
>> > diff --git a/ld/testsuite/ld-aarch64/copy-reloc-protected.d b/ld/testsuite/ld-aarch64/copy-reloc-protected.d
>> > new file mode 100644
>> > index 00000000000..99a356a3df6
>> > --- /dev/null
>> > +++ b/ld/testsuite/ld-aarch64/copy-reloc-protected.d
>> > @@ -0,0 +1,2 @@
>> > +.*: tmpdir/copy-reloc-exe.o: copy relocation against non-copyable protected symbol `global_a'
>> > +#...
>> > diff --git a/ld/testsuite/ld-aarch64/protected.s b/ld/testsuite/ld-aarch64/protected.s
>> > new file mode 100644
>> > index 00000000000..eb3fb402dc4
>> > --- /dev/null
>> > +++ b/ld/testsuite/ld-aarch64/protected.s
>> > @@ -0,0 +1,8 @@
>> > +.global global_a
>> > +.protected global_a
>> > +.type global_a, %object
>> > +.size global_a, 4
>> > +
>> > +.data
>> > +global_a:
>> > +.word 0xcafedead
>> > --
>> > 2.36
>> >

glibc now has a diagnostic for copy relocations on a protected symbol
https://sourceware.org/git/?p=glibc.git;a=commit;h=7374c02b683b7110b853a32496a619410364d70b :)
Let's catch the issue on ld side, too.

Ping