Message-ID: <CAKv+Gu_qGN8SG7ajkF7zAoAJd=qskC1oonmjzsqzZyGb9rYGLA@mail.gmail.com>
Date:   Tue, 9 Apr 2019 10:43:18 -0700
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Raphael Gault <raphael.gault@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Julien Thierry <julien.thierry@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 0/6] objtool: Add support for Arm64

On Tue, 9 Apr 2019 at 06:53, Raphael Gault <raphael.gault@....com> wrote:
>
> Hi,
>
> As of now, objtool only supports the x86_64 architecture but the
> groundwork has already been done in order to add support for other
> architecture without too much effort.
>
> This series of patches adds support for the arm64 architecture
> based on the Armv8.5 Architecture Reference Manual.
>

I think it makes sense to clarify *why* we want this on arm64. Also,
we should identify things that objtool does today that maybe we don't
want on arm64, rather than buy into all of it by default.

> * Patch 1 adapts the existing code to be able to add support for other
>   architecture.
> * Patch 2 provide implementation of the required function for the arm64
>   architecture.
> * Patch 3 adapts the checking of the stack state for the arm64
>   architecture.
> * Patch 4 & 5 fix some warning objtool raised in some particular
>   functions of ~/arch/arm64/kernel/sleep.S. Patch 4 add a macro to
>   signal that some function should be ignored by objtool.
> * Patch 6 enables stack validation for arm64.
>
> Theses patches should provide support for the main cases and behaviour.
> However a few corner cases are not yet handled by objtool:
>
> * In the `~/arch/arm64/crypto/` directory, I noticed that some plain
>   data are sometimes stored in the `.text` section causing objtool to mistake
>   this for instructions and trying (and failing) to interprete them.  If someone
>   could explain to me why we store data directly in the .text section I would
>   appreciate it.
>

Just for convenience, basically. Not specifying a section at all when
emitting a literal amounts to putting it into .text, and a a bonus, it
is guaranteed to be in range for a ADR instructions (which is not the
case when the code is built into the kernel rather than enabled as a
module)

Due to Spectre I have already updated some of the code so larger
tables are moved into .rodata (since literal data might contain binary
sequences that are usable as spectre gadgets), but some work remains
to be done.

> * In the support for arm32 architecture such as in `~/arch/arm64/kernel/kuser32.S`
>   some A32 instructions are used but such instructions are not understood by
>   objtool causing a warning.
>
> I also have a few unclear points I would like to bring to your
> attention:
>
> * For x86_64, when looking for a symbol relocation with explicit
>   addend, objtool systematically adds a +4 offset to the addend.
>   I don't understand why even if I have a feeling it is related
>   to the type of relacation.
>
> * I currently don't have a clear understanding about how switch-tables
>   are generated on arm64 and how to retrieve them (based on relocations).
>
> Please provide me with any feedback and comments as well on the content
> than the style of these patches.
>
> Thanks,
>
> Raphael
>
> ->
>
> Raphael Gault (6):
>   objtool: Refactor code to make it more suitable for multiple
>     architecture support
>   objtool: arm64: Add required implementation for supporting the aarch64
>     architecture in objtool.
>   objtool: arm64: Adapt the stack frame checks and the section analysis
>     for the arm architecture
>   arm64: assembler: Add macro to annotate asm function having non
>     standard stack-frame.
>   arm64: sleep: Add stack frame setup for __cpu_supsend_enter
>   objtool: arm64: Enable stack validation for arm64
>
>  arch/arm64/Kconfig                            |    1 +
>  arch/arm64/include/asm/assembler.h            |   18 +
>  arch/arm64/kernel/sleep.S                     |    4 +
>  tools/objtool/Build                           |    1 -
>  tools/objtool/arch.h                          |   11 +
>  tools/objtool/arch/arm64/Build                |    6 +
>  tools/objtool/arch/arm64/bit_operations.c     |   65 +
>  tools/objtool/arch/arm64/decode.c             | 2870 +++++++++++++++++
>  .../objtool/arch/arm64/include/arch_special.h |   44 +
>  .../arch/arm64/include/asm/orc_types.h        |  109 +
>  .../arch/arm64/include/bit_operations.h       |   22 +
>  tools/objtool/arch/arm64/include/cfi.h        |   76 +
>  .../objtool/arch/arm64/include/insn_decode.h  |  219 ++
>  tools/objtool/arch/arm64/orc_gen.c            |   40 +
>  tools/objtool/arch/x86/Build                  |    1 +
>  tools/objtool/arch/x86/decode.c               |  111 +
>  tools/objtool/arch/x86/include/arch_special.h |   35 +
>  tools/objtool/{ => arch/x86/include}/cfi.h    |    0
>  tools/objtool/{ => arch/x86}/orc_gen.c        |   10 +-
>  tools/objtool/check.c                         |  209 +-
>  tools/objtool/check.h                         |    1 +
>  tools/objtool/elf.c                           |    3 +-
>  tools/objtool/orc.h                           |    4 +-
>  tools/objtool/special.c                       |   18 +-
>  24 files changed, 3740 insertions(+), 138 deletions(-)
>  create mode 100644 tools/objtool/arch/arm64/Build
>  create mode 100644 tools/objtool/arch/arm64/bit_operations.c
>  create mode 100644 tools/objtool/arch/arm64/decode.c
>  create mode 100644 tools/objtool/arch/arm64/include/arch_special.h
>  create mode 100644 tools/objtool/arch/arm64/include/asm/orc_types.h
>  create mode 100644 tools/objtool/arch/arm64/include/bit_operations.h
>  create mode 100644 tools/objtool/arch/arm64/include/cfi.h
>  create mode 100644 tools/objtool/arch/arm64/include/insn_decode.h
>  create mode 100644 tools/objtool/arch/arm64/orc_gen.c
>  create mode 100644 tools/objtool/arch/x86/include/arch_special.h
>  rename tools/objtool/{ => arch/x86/include}/cfi.h (100%)
>  rename tools/objtool/{ => arch/x86}/orc_gen.c (96%)
>
> --
> 2.17.1
>
>
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