[PATCH, BFD, LD, AArch64, 3/4] Add --bti to enable BTI and select BTI enabled PLTs but also warn for missing NOTE sections.
Sudakshina Das
Sudi.Das@arm.com
Wed Mar 6 10:36:00 GMT 2019
Hi
On 06/03/2019 10:34, Sudakshina Das wrote:
> Hi
>
> On 06/03/2019 10:30, Sudakshina Das wrote:
>> Hi
>>
>> On 06/03/2019 10:26, Sudakshina Das wrote:
>>> Hi
>>>
>>> This patch series is aimed at giving support for the new Armv8.3-A
>>> Pointer Authentication and Armv8.5-A Branch Target Identification
>>> feature in the linker.
>>>
>>> In order to support these, we propose to make the following changes:
>>> 1) We have defined .note.gnu.property for AArch64.
>>> 2) We have defined a new Program Property type
>>> GNU_PROPERTY_AARCH64_FEATURE_1_AND and used 2 bits to represent
>>> BTI and PAC respectively.
>>> - GNU_PROPERTY_AARCH64_FEATURE_1_BTI
>>> - GNU_PROPERTY_AARCH64_FEATURE_1_PAC (We have only reserved this bit
>>> for now.)
>>> 3) We also need custom PLTs when these features are turned on and thus
>>> we have defined the following processor-specific dynamic array tags:
>>> - DT_AARCH64_BTI_PLT
>>> - DT_AARCH64_PAC_PLT
>>> Details of these can be found in the new AArch64 ELF documentation:
>>> https://developer.arm.com/docs/ihi0056/latest/elf-for-the-arm-64-bit-architecture-aarch64-abi-2018q4
>>>
>>>
>>> Command line options:
>>> We introduce a new set of command line options for the linker in
>>> order to support the correct PLTs
>>> 1) --pac-plt : In the presence of this option, the linker uses a PAC
>>> enabled PLT. It also uses the dynamic tag DT_AARCH64_PAC_PLT to
>>> reflect the same. Other tools like Objdump can use this to determine
>>> the size of the PLTs.
>>> 2) --bti: In the presence of this option, the linker enables BTI with
>>> the GNU_PROPERTY_AARCH64_FEATURE_1_BTI feature and also uses a BTI
>>> enabled PLT. It also uses the dynamic tag DT_AARCH64_BTI_PLT to
>>> reflect the choice of the PLTs. Other tools like Objdump can use this
>>> to determine the size of the PLTs. Using this option can give a
>>> warning if not all input objects are marked with
>>> GNU_PROPERTY_AARCH64_FEATURE_1_BTI.
>>> 3)--bti-nowarn - Same as above but does not emit any warnings.
>>>
>>> In terms of the PLTs, in the presence of both --pac-plt and
>>> --bti/--bti-nowarn, the linker chooses the PLTs protected with both
>>> BTI and PAC and uses both DT_AARCH64_PAC_PLT and DT_AARCH64_BTI_PLT.
>>>
>>> Interaction between Command line arguments and GNU NOTE section
>>> 1) For PAC, in the presence of --pac-plt along with BIND_NOW, the
>>> linker can choose to ignore the pac-plt directive and use smaller
>>> PLTs without compromising on security,
>>> 2) For BTI, the linker must also check for the
>>> GNU_PROPERTY_AARCH64_FEATURE_1_BTI in its input. If all inputs have
>>> GNU_PROPERTY_AARCH64_FEATURE_1_BTI, the final output will also be
>>> marked as such. The PLT should also be protected with a BTI PLT in
>>> this case. Thus even if there is no linker option to use BTI PLT, the
>>> linker
>>> should be able to use them depending on the NOTE section. The user
>>> can use the linker option --bti, to make sure that their intention of
>>> having all input objects (and hence the output) marked with BTI is
>>> not disrupted by any stray objects as this option will warn about it.
>>>
>>>
>>> The following patches implement these changes as follows:
>>> [1/4] Add support for GNU PROPERTIES in AArch64 for BTI and PAC:
>>> [2/4] Add --bti-nowarn to enable BTI without warning and to select
>>> BTI enabled PLTs
>>> [3/4] Add --bti to enable BTI and select BTI enabled PLTs but also
>>> warn for missing NOTE sections.
>>> [4/4] Add --pac-plt to enable PLTs protected with PAC.
>>>
>>> This is my first time making such intrusive changes to the linker.
>>> Please be kind :P
>>>
>>> Thanks
>>> Sudi
>>
>> This is part of the patch series to add support for BTI and
>> PAC in AArch64 linker.
>>
>> This patch implements the following:
>> 1) This extends in the gnu property support in the linker for
>> AArch64 by defining backend hooks for elf_backend_setup_gnu_properties,
>> elf_backend_merge_gnu_properties and elf_backend_parse_gnu_properties.
>> 2) It defines AArch64 specific GNU property
>> GNU_PROPERTY_AARCH64_FEATURE_1_AND and 2 bit for BTI and PAC in it.
>> 3) It also adds support in readelf.c to read and print these new
>> GNU properties in AArch64.
>> All these are made according to the new AArch64 ELF ABI
>> https://developer.arm.com/docs/ihi0056/latest/elf-for-the-arm-64-bit-architecture-aarch64-abi-2018q4
>>
>>
>> Build and regression tests all pass on aarch64-none-linux-gnu and
>> new tests are added.
>>
>> Is this ok for trunk?
>>
>> Thanks
>> Sudi
>>
>> *** bfd/ChangeLog ***
>>
>> 2019-xx-xx Sudakshina Das <sudi.das@arm.com>
>>
>> * elf-properties.c (_bfd_elf_link_setup_gnu_properties): Exclude
>> linker created inputs from merge.
>> * elfnn-aarch64.c (struct elf_aarch64_obj_tdata): Add field for
>> GNU_PROPERTY_AARCH64_FEATURE_1_AND properties.
>> (elfNN_aarch64_link_setup_gnu_properties): New.
>> (elfNN_aarch64_merge_gnu_properties): New.
>> (elf_backend_setup_gnu_properties): Define for AArch64.
>> (elf_backend_merge_gnu_properties): Likewise.
>> * elfxx-aarch64.c (_bfd_aarch64_elf_link_setup_gnu_properties):
>> Define.
>> (_bfd_aarch64_elf_parse_gnu_properties): Define.
>> (_bfd_aarch64_elf_merge_gnu_properties): Define.
>> * elfxx-aarch64.h (_bfd_aarch64_elf_link_setup_gnu_properties):
>> Declare.
>> (_bfd_aarch64_elf_parse_gnu_properties): Declare.
>> (_bfd_aarch64_elf_merge_gnu_properties): Declare.
>> (elf_backend_parse_gnu_properties): Define for AArch64.
>>
>> *** binutils/ChangeLog ***
>>
>> 2019-xx-xx Sudakshina Das <sudi.das@arm.com>
>>
>> * readelf.c (decode_aarch64_feature_1_and): New.
>> (print_gnu_property_note): Add case for AArch64 gnu notes.
>>
>> *** include/ChangeLog ***
>>
>> 2019-xx-xx Sudakshina Das <sudi.das@arm.com>
>>
>> * elf/common.h (GNU_PROPERTY_AARCH64_FEATURE_1_AND): New.
>> (GNU_PROPERTY_AARCH64_FEATURE_1_BTI): New.
>> (GNU_PROPERTY_AARCH64_FEATURE_1_PAC): New.
>>
>> *** ld/ChangeLog ***
>>
>> 2019-xx-xx Sudakshina Das <sudi.das@arm.com>
>>
>> * NEWS: Document GNU_PROPERTY_AARCH64_FEATURE_1_BTI and
>> GNU_PROPERTY_AARCH64_FEATURE_1_PAC.
>> * testsuite/ld-aarch64/aarch64-elf.exp: Add run commands for new
>> tests.
>> * testsuite/ld-aarch64/property-bti-pac1.d: New test.
>> * testsuite/ld-aarch64/property-bti-pac1.s: New test.
>> * testsuite/ld-aarch64/property-bti-pac2.d: New test.
>> * testsuite/ld-aarch64/property-bti-pac2.s: New test.
>> * testsuite/ld-aarch64/property-bti-pac3.d: New test.
>
> This is part of the patch series to add support for BTI and
> PAC in AArch64 linker.
>
> 1) This patch adds a new ld command line option: --bti-nowarn.
> In the presence of this option, the linker enables BTI with the
> GNU_PROPERTY_AARCH64_FEATURE_1_BTI feature. This gives no warning
> in case of missing gnu notes for BTI in inputs.
> 2) It also defines a new set of BTI enabled PLTs. These are used either
> when all the inputs are marked with GNU_PROPERTY_AARCH64_FEATURE_1_BTI
> or when the new --bti-nowarn option is used. This required adding new
> fields in elf_aarch64_link_hash_table so that we could make the PLT
> related information more generic.
> 3) It also defines a dynamic tag DT_AARCH64_BTI_PLT. The linker uses
> this whenever it picks BTI enabled PLTs.
> All these are made according to the new AArch64 ELF ABI
> https://developer.arm.com/docs/ihi0056/latest/elf-for-the-arm-64-bit-architecture-aarch64-abi-2018q4
>
>
> Build and regression tests all pass on aarch64-none-linux-gnu and
> new tests are added.
>
> Is this ok for trunk?
>
> Thanks
> Sudi
>
> *** bfd/ChangeLog ***
>
> 2019-xx-xx Sudakshina Das <sudi.das@arm.com>
> Szabolcs Nagy <szabolcs.nagy@arm.com>
>
> * bfd-in.h (aarch64_plt_type, aarch64_enable_bti_type): New.
> (aarch64_bti_pac_info): New.
> (bfd_elf64_aarch64_set_options): Add aarch64_bti_pac_info argument.
> (bfd_elf32_aarch64_set_options): Likewise.
> * bfd-in2.h: Regenerate
> * elfnn-aarch64.c (PLT_BTI_ENTRY_SIZE): New.
> (PLT_BTI_SMALL_ENTRY_SIZE, PLT_BTI_TLSDESC_ENTRY_SIZE): New.
> (elfNN_aarch64_small_plt0_bti_entry): New.
> (elfNN_aarch64_small_plt_bti_entry): New.
> (elfNN_aarch64_tlsdesc_small_plt_bti_entry): New.
> (elf_aarch64_obj_tdata): Add no_enable_bti_warn and plt_type fields.
> (elf_aarch64_link_hash_table): Add plt0_entry, plt_entry and
> tlsdesc_plt_entry_size fields.
> (elfNN_aarch64_link_hash_table_create): Initialise the new fields.
> (setup_plt_values): New helper function.
> (bfd_elfNN_aarch64_set_options): Use new bp_info to set plt sizes and
> bti enable type.
> (elfNN_aarch64_allocate_dynrelocs): Use new size members instead of
> fixed macros.
> (elfNN_aarch64_size_dynamic_sections): Likewise and add checks.
> (elfNN_aarch64_create_small_pltn_entry): Use new generic pointers
> to plt stubs instead of fixed ones and update filling them according
> to the need for bti.
> (elfNN_aarch64_init_small_plt0_entry): Likewise.
> (elfNN_aarch64_finish_dynamic_sections): Likewise.
> (get_plt_type, elfNN_aarch64_get_synthetic_symtab): New.
> (elfNN_aarch64_plt_sym_val): Update size accordingly.
> (elfNN_aarch64_link_setup_gnu_properties): Set up plts if BTI GNU NOTE
> is set.
> (bfd_elfNN_get_synthetic_symtab): Define.
>
> *** binutils/ChangeLog ***
>
> 2019-xx-xx Sudakshina Das <sudi.das@arm.com>
> Szabolcs Nagy <szabolcs.nagy@arm.com>
>
> * readelf.c (get_aarch64_dynamic_type): New.
> (get_dynamic_type): Use above for EM_AARCH64.
> (dynamic_section_aarch64_val): New.
> (process_dynamic_section): Use above for EM_AARCH64.
>
> *** include/ChangeLog ***
>
> 2019-xx-xx Sudakshina Das <sudi.das@arm.com>
> Szabolcs Nagy <szabolcs.nagy@arm.com>
>
> * elf/aarch64.h (DT_AARCH64_BTI_PLT): New.
>
> *** ld/ChangeLog ***
>
> 2019-xx-xx Sudakshina Das <sudi.das@arm.com>
> Szabolcs Nagy <szabolcs.nagy@arm.com>
>
> * NEWS: Document --bti-nowarn.
> * emultempl/aarch64elf.em (plt_type, bti_type, OPTION_BTI_NOWARN):
> New.
> (PARSE_AND_LIST_SHORTOPTS, PARSE_AND_LIST_OPTIONS): Add bti-nowarn.
> (PARSE_AND_LIST_ARGS_CASES): Handle OPTION_BTI_NOWARN.
> * testsuite/ld-aarch64/aarch64-elf.exp: Add all the tests below.
> * testsuite/ld-aarch64/bti-plt-1.d: New test.
> * testsuite/ld-aarch64/bti-plt-1.s: New test.
> * testsuite/ld-aarch64/bti-plt-2.d: New test.
> * testsuite/ld-aarch64/bti-plt-3.d: New test.
> * testsuite/ld-aarch64/bti-plt-4.d: New test.
> * testsuite/ld-aarch64/bti-plt-5.d: New test.
> * testsuite/ld-aarch64/bti-plt-so.s: New test.
> * testsuite/ld-aarch64/bti-plt.ld: New test.
This is part of the patch series to add support for BTI and
PAC in AArch64 linker.
This patch adds a new ld command line option: --bti.
In the presence of this option, the linker enables BTI with the
GNU_PROPERTY_AARCH64_FEATURE_1_BTI feature. It also uses the BTI
enabled PLTs and marks with DT_AARCH64_BTI_PLT. This also gives a
warning in case of missing gnu notes for BTI in inputs.
All these are made according to the new AArch64 ELF ABI
https://developer.arm.com/docs/ihi0056/latest/elf-for-the-arm-64-bit-architecture-aarch64-abi-2018q4
Build and regression tests all pass on aarch64-none-linux-gnu and
new tests are added.
Is this ok for trunk?
Thanks
Sudi
*** bfd/ChangeLog ***
2019-xx-xx Sudakshina Das <sudi.das@arm.com>
* elfnn-aarch64.c (elfNN_aarch64_merge_gnu_properties): Give out
warning with --bti and mising BTI NOTE SECTION.
*** ld/ChangeLog ***
2019-xx-xx Sudakshina Das <sudi.das@arm.com>
* NEWS: Document --bti.
* emultempl/aarch64elf.em (OPTION_BTI_WARN): Define.
(PARSE_AND_LIST_LONGOPTS, PARSE_AND_LIST_OPTIONS): Add --bti.
(PARSE_AND_LIST_ARGS_CASES): Handle OPTION_BTI_WARN.
* testsuite/ld-aarch64/aarch64-elf.exp: Add below tests.
* testsuite/ld-aarch64/bti-plt-6.d: New test.
* testsuite/ld-aarch64/bti-plt-7.d: New test.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: rb10236.patch
Type: text/x-patch
Size: 5654 bytes
Desc: rb10236.patch
URL: <https://sourceware.org/pipermail/binutils/attachments/20190306/03ec15bd/attachment.bin>
More information about the Binutils
mailing list