Re: [PATCH v2 01/17] MdePkg/ProcessorBind AARCH64: Add asm macro to emit GNU BTI note

["Leif Lindholm" <quic_llindhol@quicinc.com>]

On Mon, Mar 27, 2023 at 13:00:56 +0200, Ard Biesheuvel wrote:
> Implement a CPP macro that can be called from .S files to emit the .note
> section carrying the annotation that informs the linker that the object
> file is compatible with BTI control flow integrity checks.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
>  MdePkg/Include/AArch64/ProcessorBind.h | 31 ++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/MdePkg/Include/AArch64/ProcessorBind.h b/MdePkg/Include/AArch64/ProcessorBind.h
> index abe2571245c665f3..11814f1ffaef698a 100644
> --- a/MdePkg/Include/AArch64/ProcessorBind.h
> +++ b/MdePkg/Include/AArch64/ProcessorBind.h
> @@ -186,6 +186,37 @@ typedef INT64 INTN;
>  #define GCC_ASM_IMPORT(func__)  \
>           .extern  _CONCATENATE (__USER_LABEL_PREFIX__, func__)
>  
> +#if defined(__ARM_FEATURE_BTI_DEFAULT) && __ARM_FEATURE_BTI_DEFAULT == 1
> +#define AARCH64_BTI(__type)                                        \
> +    .ifnc         __type,                                         ;\
> +    bti           __type                                          ;\
> +    .endif                                                        ;\
> +    .ifndef       .Lgnu_bti_notesize                              ;\
> +    .pushsection  .note.gnu.property, "a"                         ;\
> +    .set          NT_GNU_PROPERTY_TYPE_0, 0x5                     ;\
> +    .set          GNU_PROPERTY_AARCH64_FEATURE_1_AND, 0xc0000000  ;\
> +    .set          GNU_PROPERTY_AARCH64_FEATURE_1_BTI, 0x1         ;\
> +    .align        3                                               ;\
> +    .long         .Lnamesize                                      ;\
> +    .long         .Lgnu_bti_notesize                              ;\
> +    .long         NT_GNU_PROPERTY_TYPE_0                          ;\
> +0:  .asciz        "GNU"                                           ;\
> +    .set          .Lnamesize, . - 0b                              ;\
> +    .align        3                                               ;\
> +1:  .long         GNU_PROPERTY_AARCH64_FEATURE_1_AND              ;\
> +    .long         .Lvalsize                                       ;\
> +2:  .long         GNU_PROPERTY_AARCH64_FEATURE_1_BTI              ;\
> +    .set          .Lvalsize, . - 2b                               ;\
> +    .align        3                                               ;\
> +    .set          .Lgnu_bti_notesize, . - 1b                      ;\
> +    .popsection                                                   ;\
> +    .endif
> +#endif
> +
> +#endif

Is that second endif superflouous?

/
    Leif

> +
> +#ifndef AARCH64_BTI
> +#define AARCH64_BTI(__type)
>  #endif
>  
>  /**
> -- 
> 2.39.2
>