Re: [PATCH] x86: Make protected symbols local for -shared

[Fangrui Song <i@maskray.me>]

On 2022-06-26, H.J. Lu wrote:
>On Sat, Jun 25, 2022 at 10:44 AM Fangrui Song <i@maskray.me> wrote:
>>
>> Call _bfd_elf_symbol_refs_local_p with local_protected==true.  This has
>> 2 noticeable effects for -shared:
>>
>> * GOT-generating relocations referencing a protected data symbol no
>>   longer lead to a GLOB_DAT (similar to a hidden symbol).
>> * Direct access relocations (e.g. R_X86_64_PC32) no longer has the
>>   confusing diagnostic below.
>>
>>     __attribute__((visibility("protected"))) void *foo() {
>>       return (void *)foo;
>>     }
>>
>>     // gcc -fpic -shared -fuse-ld=bfd
>>     relocation R_X86_64_PC32 against protected symbol `foo' can not be used when making a shared object
>>
>> The new behavior matches arm, aarch64 (commit
>> 83c325007c5599fa9b60b8d5f7b84842160e1d1b), and powerpc ports, and other
>> linkers: gold and ld.lld.
>>
>> Note: if some code tries to use direct access relocations to take the
>> address of foo, the pointer equality will break, but the error should be
>> reported on the executable link, not on the innocent shared object link.
>> glibc 2.36 will give a warning at relocation resolving time.
>
>It should be controlled by -z [no]indirect-extern-access.   Can you enable
>-z  indirect-extern-access with -shared by default instead?

If I set `link_info.indirect_extern_access = 1;` in ld/ldmain.c,
bfd/elf-properties.c:654 will create a
GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS note.
This will probably be unexpected (and check-ld will have 280+ failures).

>> With this change, `#define elf_backend_extern_protected_data 1` is no
>> longer effective.  Just remove it.
>>
>> Remove the test "Run protected-func-1 without PIE" since -fno-pic
>> address taken operation in the executable doesn't work with protected
>> symbol in a shared object by default.  Similarly, remove
>> protected-data-1a and protected-data-1b.  protected-data-1b can be made
>> working by removing HAVE_LD_PIE_COPYRELOC from GCC
>> (https://sourceware.org/pipermail/gcc-patches/2022-June/596678.html).
>> ---
>>  bfd/elf32-i386.c                      |  1 -
>>  bfd/elf64-x86-64.c                    |  1 -
>>  bfd/elfxx-x86.c                       |  2 +-
>>  ld/testsuite/ld-i386/protected1.d     |  4 +++-
>>  ld/testsuite/ld-i386/protected3.d     |  2 +-
>>  ld/testsuite/ld-i386/protected6a.d    |  4 +++-
>>  ld/testsuite/ld-x86-64/pr24151a-x32.d |  4 +++-
>>  ld/testsuite/ld-x86-64/pr24151a.d     |  4 +++-
>>  ld/testsuite/ld-x86-64/protected1.d   |  4 +++-
>>  ld/testsuite/ld-x86-64/protected3.d   |  2 +-
>>  ld/testsuite/ld-x86-64/protected6a.d  |  4 +++-
>>  ld/testsuite/ld-x86-64/protected7a.d  |  4 +++-
>>  ld/testsuite/ld-x86-64/x86-64.exp     | 27 ---------------------------
>>  13 files changed, 24 insertions(+), 39 deletions(-)
>>
>> diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
>> index e4106d9fd3b..c3c46795731 100644
>> --- a/bfd/elf32-i386.c
>> +++ b/bfd/elf32-i386.c
>> @@ -4424,7 +4424,6 @@ elf_i386_link_setup_gnu_properties (struct bfd_link_info *info)
>>  #define elf_backend_got_header_size    12
>>  #define elf_backend_plt_alignment      4
>>  #define elf_backend_dtrel_excludes_plt 1
>> -#define elf_backend_extern_protected_data 1
>>  #define elf_backend_caches_rawsize     1
>>  #define elf_backend_want_dynrelro      1
>>
>> diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
>> index 6154a70bdd7..aaa5f1496b9 100644
>> --- a/bfd/elf64-x86-64.c
>> +++ b/bfd/elf64-x86-64.c
>> @@ -5275,7 +5275,6 @@ elf_x86_64_special_sections[]=
>>  #define elf_backend_got_header_size        (GOT_ENTRY_SIZE*3)
>>  #define elf_backend_rela_normal                    1
>>  #define elf_backend_plt_alignment          4
>> -#define elf_backend_extern_protected_data   1
>>  #define elf_backend_caches_rawsize         1
>>  #define elf_backend_dtrel_excludes_plt     1
>>  #define elf_backend_want_dynrelro          1
>> diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
>> index acb2cc8528d..18f3d335458 100644
>> --- a/bfd/elfxx-x86.c
>> +++ b/bfd/elfxx-x86.c
>> @@ -3094,7 +3094,7 @@ _bfd_x86_elf_link_symbol_references_local (struct bfd_link_info *info,
>>       2. When building executable, there is no dynamic linker.  Or
>>       3. or "-z nodynamic-undefined-weak" is used.
>>     */
>> -  if (SYMBOL_REFERENCES_LOCAL (info, h)
>> +  if (_bfd_elf_symbol_refs_local_p (h, info, 1)
>>        || (h->root.type == bfd_link_hash_undefweak
>>           && (ELF_ST_VISIBILITY (h->other) != STV_DEFAULT
>>               || (bfd_link_executable (info)
>> diff --git a/ld/testsuite/ld-i386/protected1.d b/ld/testsuite/ld-i386/protected1.d
>> index a3cb5cef140..531645b8fe8 100644
>> --- a/ld/testsuite/ld-i386/protected1.d
>> +++ b/ld/testsuite/ld-i386/protected1.d
>> @@ -1,3 +1,5 @@
>>  #as: --32
>>  #ld: -shared -melf_i386
>> -#error: .*relocation R_386_GOTOFF against protected function `foo' can not be used when making a shared object
>> +#readelf: -rW
>> +#...
>> +There are no relocations in this file.
>> diff --git a/ld/testsuite/ld-i386/protected3.d b/ld/testsuite/ld-i386/protected3.d
>> index c3a6888d900..77367c4738f 100644
>> --- a/ld/testsuite/ld-i386/protected3.d
>> +++ b/ld/testsuite/ld-i386/protected3.d
>> @@ -8,7 +8,7 @@
>>  Disassembly of section .text:
>>
>>  0+[a-f0-9]+ <bar>:
>> -[      ]*[a-f0-9]+:    8b 81 [a-f0-9][a-f0-9] [a-f0-9][a-f0-9] ff ff           mov    -0x[a-f0-9]+\(%ecx\),%eax
>> +[      ]*[a-f0-9]+:    8d 81 00 00 00 00       lea    0x0\(%ecx\),%eax
>>  [      ]*[a-f0-9]+:    8b 00                   mov    \(%eax\),%eax
>>  [      ]*[a-f0-9]+:    c3                      ret
>>  #pass
>> diff --git a/ld/testsuite/ld-i386/protected6a.d b/ld/testsuite/ld-i386/protected6a.d
>> index 7dc350432f4..4d3873239f9 100644
>> --- a/ld/testsuite/ld-i386/protected6a.d
>> +++ b/ld/testsuite/ld-i386/protected6a.d
>> @@ -1,4 +1,6 @@
>>  #source: protected6.s
>>  #as: --32
>>  #ld: -shared -melf_i386
>> -#error: .*relocation R_386_GOTOFF against protected data `foo' can not be used when making a shared object
>> +#readelf: -rW
>> +#...
>> +There are no relocations in this file.
>> diff --git a/ld/testsuite/ld-x86-64/pr24151a-x32.d b/ld/testsuite/ld-x86-64/pr24151a-x32.d
>> index 130611ddf49..1f49b655f7d 100644
>> --- a/ld/testsuite/ld-x86-64/pr24151a-x32.d
>> +++ b/ld/testsuite/ld-x86-64/pr24151a-x32.d
>> @@ -1,4 +1,6 @@
>>  #source: pr24151a.s
>>  #as: --x32
>>  #ld: -shared -melf32_x86_64
>> -#error: .*relocation R_X86_64_PC32 against protected symbol `foo' can not be used when making a shared object
>> +#readelf: -rW
>> +#...
>> +There are no relocations in this file.
>> diff --git a/ld/testsuite/ld-x86-64/pr24151a.d b/ld/testsuite/ld-x86-64/pr24151a.d
>> index 783b85a1a6f..6c48e383e01 100644
>> --- a/ld/testsuite/ld-x86-64/pr24151a.d
>> +++ b/ld/testsuite/ld-x86-64/pr24151a.d
>> @@ -1,3 +1,5 @@
>>  #as: --64
>>  #ld: -shared -melf_x86_64
>> -#error: .*relocation R_X86_64_PC32 against protected symbol `foo' can not be used when making a shared object
>> +#readelf: -rW
>> +#...
>> +There are no relocations in this file.
>> diff --git a/ld/testsuite/ld-x86-64/protected1.d b/ld/testsuite/ld-x86-64/protected1.d
>> index 783b85a1a6f..6c48e383e01 100644
>> --- a/ld/testsuite/ld-x86-64/protected1.d
>> +++ b/ld/testsuite/ld-x86-64/protected1.d
>> @@ -1,3 +1,5 @@
>>  #as: --64
>>  #ld: -shared -melf_x86_64
>> -#error: .*relocation R_X86_64_PC32 against protected symbol `foo' can not be used when making a shared object
>> +#readelf: -rW
>> +#...
>> +There are no relocations in this file.
>> diff --git a/ld/testsuite/ld-x86-64/protected3.d b/ld/testsuite/ld-x86-64/protected3.d
>> index 57950e4d6b6..ba63991582f 100644
>> --- a/ld/testsuite/ld-x86-64/protected3.d
>> +++ b/ld/testsuite/ld-x86-64/protected3.d
>> @@ -8,7 +8,7 @@
>>  Disassembly of section .text:
>>
>>  0+[a-f0-9]+ <bar>:
>> -[      ]*[a-f0-9]+:    48 8b 05 ([0-9a-f]{2} ){4} *    mov    0x[a-f0-9]+\(%rip\),%rax        # [a-f0-9]+ <.*>
>> +[      ]*[a-f0-9]+:    48 8d 05 ([0-9a-f]{2} ){4} *    lea    0x[a-f0-9]+\(%rip\),%rax        # [a-f0-9]+ <.*>
>>  [      ]*[a-f0-9]+:    8b 00                   mov    \(%rax\),%eax
>>  [      ]*[a-f0-9]+:    c3                      ret
>>  #pass
>> diff --git a/ld/testsuite/ld-x86-64/protected6a.d b/ld/testsuite/ld-x86-64/protected6a.d
>> index 3a7963ffd2f..50d6430b577 100644
>> --- a/ld/testsuite/ld-x86-64/protected6a.d
>> +++ b/ld/testsuite/ld-x86-64/protected6a.d
>> @@ -1,4 +1,6 @@
>>  #source: protected6.s
>>  #as: --64
>>  #ld: -shared -melf_x86_64
>> -#error: .*relocation R_X86_64_GOTOFF64 against protected data `foo' can not be used when making a shared object
>> +#readelf: -rW
>> +#...
>> +There are no relocations in this file.
>> diff --git a/ld/testsuite/ld-x86-64/protected7a.d b/ld/testsuite/ld-x86-64/protected7a.d
>> index 3082084a7b8..3974246a2a8 100644
>> --- a/ld/testsuite/ld-x86-64/protected7a.d
>> +++ b/ld/testsuite/ld-x86-64/protected7a.d
>> @@ -1,4 +1,6 @@
>>  #source: protected7.s
>>  #as: --64
>>  #ld: -shared -melf_x86_64
>> -#error: .*relocation R_X86_64_GOTOFF64 against protected function `foo' can not be used when making a shared object
>> +#readelf: -rW
>> +#...
>> +There are no relocations in this file.
>> diff --git a/ld/testsuite/ld-x86-64/x86-64.exp b/ld/testsuite/ld-x86-64/x86-64.exp
>> index 5e5636bcebe..a096c0b9d0f 100644
>> --- a/ld/testsuite/ld-x86-64/x86-64.exp
>> +++ b/ld/testsuite/ld-x86-64/x86-64.exp
>> @@ -1832,15 +1832,6 @@ if { [isnative] && [check_compiler_available] } {
>>             "pr23997" \
>>             "pass.out" \
>>         ] \
>> -       [list \
>> -           "Run protected-func-1 without PIE" \
>> -           "$NOPIE_LDFLAGS -Wl,--no-as-needed tmpdir/libprotected-func-1.so" \
>> -           "-Wa,-mx86-used-note=yes" \
>> -           { protected-func-1b.c } \
>> -           "protected-func-1a" \
>> -           "pass.out" \
>> -           "$NOPIE_CFLAGS" \
>> -       ] \
>>         [list \
>>             "Run protected-func-1 with PIE" \
>>             "-Wl,--no-as-needed -pie tmpdir/libprotected-func-1.so" \
>> @@ -1904,24 +1895,6 @@ if { [isnative] && [check_compiler_available] } {
>>             "pass.out" \
>>             "-fPIE" \
>>         ] \
>> -       [list \
>> -           "Run protected-data-1a without PIE" \
>> -           "$NOPIE_LDFLAGS -Wl,--no-as-needed tmpdir/libprotected-data-1a.so" \
>> -           "-Wa,-mx86-used-note=yes" \
>> -           { protected-data-1b.c } \
>> -           "protected-data-1a" \
>> -           "pass.out" \
>> -           "$NOPIE_CFLAGS" \
>> -       ] \
>> -       [list \
>> -           "Run protected-data-1b with PIE" \
>> -           "-Wl,--no-as-needed -pie tmpdir/libprotected-data-1a.so" \
>> -           "-Wa,-mx86-used-note=yes" \
>> -           { protected-data-1b.c } \
>> -           "protected-data-1b" \
>> -           "pass.out" \
>> -           "-fPIE" \
>> -       ] \
>>         [list \
>>             "Run protected-data-2a without PIE" \
>>             "$NOPIE_LDFLAGS -Wl,--no-as-needed tmpdir/libprotected-data-2a.so" \
>> --
>> 2.37
>>
>
>
>-- 
>H.J.