Re: [PATCH] x86-64: Fix the tcb field load for x32 [BZ #31185]

Re: [PATCH] x86-64: Fix the tcb field load for x32 [BZ #31185]

[H.J. Lu]

On Wed, Dec 20, 2023 at 7:42 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> _dl_tlsdesc_undefweak and _dl_tlsdesc_dynamic access the thread pointer
> via the tcb field in TCB:
>
> _dl_tlsdesc_undefweak:
>         _CET_ENDBR
>         movq    8(%rax), %rax
>         subq    %fs:0, %rax
>         ret
>
> _dl_tlsdesc_dynamic:
>         ...
>         subq    %fs:0, %rax
>         movq    -8(%rsp), %rdi
>         ret
>
> Since the tcb field in TCB is a pointer, %fs:0 is a 32-bit location,
> not 64-bit. It should use "sub %fs:0, %RAX_LP" instead.  Since
> _dl_tlsdesc_undefweak returns ptrdiff_t and _dl_make_tlsdesc_dynamic
> returns void *, RAX_LP is appropriate here for x32 and x86-64.  This
> fixes BZ #31185.
> ---
>  sysdeps/x86_64/dl-tlsdesc.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/sysdeps/x86_64/dl-tlsdesc.S b/sysdeps/x86_64/dl-tlsdesc.S
> index c4823547d7..4579424bf7 100644
> --- a/sysdeps/x86_64/dl-tlsdesc.S
> +++ b/sysdeps/x86_64/dl-tlsdesc.S
> @@ -61,7 +61,7 @@ _dl_tlsdesc_return:
>  _dl_tlsdesc_undefweak:
>         _CET_ENDBR
>         movq    8(%rax), %rax
> -       subq    %fs:0, %rax
> +       sub     %fs:0, %RAX_LP
>         ret
>         cfi_endproc
>         .size   _dl_tlsdesc_undefweak, .-_dl_tlsdesc_undefweak
> @@ -116,7 +116,7 @@ _dl_tlsdesc_dynamic:
>         addq    TLSDESC_MODOFF(%rdi), %rax
>  .Lret:
>         movq    -16(%rsp), %rsi
> -       subq    %fs:0, %rax
> +       sub     %fs:0, %RAX_LP
>         movq    -8(%rsp), %rdi
>         ret
>  .Lslow:
> --
> 2.43.0
>

I will check it in tomorrow and back it to release branches later.

Thanks.

-- 
H.J.