linux-kernel - Re: [PATCH v2 6/9] x86: elf: Use e_machine to select setup_additional

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Date:   Thu, 1 Oct 2020 14:50:29 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Robert Richter <rric@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>, kernel@...labora.com
Subject: Re: [PATCH v2 6/9] x86: elf: Use e_machine to select
 setup_additional_pages for x32

On Thu, Oct 1, 2020 at 1:59 PM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Since TIF_X32 is going away, avoid using it to find the ELF type when
> choosing which additional pages to set up.
>
> According to SysV AMD64 ABI Draft, an AMD64 ELF object using ILP32 must
> have ELFCLASS32 with (E_MACHINE == EM_X86_64), so use that ELF field to
> differentiate a x32 object from a IA32 object when executing
> start_thread in compat mode.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
> ---
>  arch/x86/entry/vdso/vma.c  | 21 ++++++++++++---------
>  arch/x86/include/asm/elf.h | 11 ++++++++---
>  2 files changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index 9185cb1d13b9..7a3cda8294a3 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -412,22 +412,25 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
>  }
>
>  #ifdef CONFIG_COMPAT
> -int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
> -                                      int uses_interp)
> +int compat_arch_setup_additional_pages_ia32(struct linux_binprm *bprm,
> +                                           int uses_interp)
>  {
> -#ifdef CONFIG_X86_X32_ABI
> -       if (test_thread_flag(TIF_X32)) {
> -               if (!vdso64_enabled)
> -                       return 0;
> -               return map_vdso_randomized(&vdso_image_x32);
> -       }
> -#endif
>  #ifdef CONFIG_IA32_EMULATION
>         return load_vdso32();
>  #else
>         return 0;
>  #endif
>  }
> +
> +int compat_arch_setup_additional_pages_x32(struct linux_binprm *bprm,
> +                                          int uses_interp)
> +{
> +#ifdef CONFIG_X86_X32_ABI
> +       if (vdso64_enabled)
> +               return map_vdso_randomized(&vdso_image_x32);
> +#endif
> +       return 0;
> +}
>  #endif
>  #else
>  int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> index 33c1c9be2e07..4d91f5b1079f 100644
> --- a/arch/x86/include/asm/elf.h
> +++ b/arch/x86/include/asm/elf.h
> @@ -388,9 +388,14 @@ struct linux_binprm;
>  #define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
>  extern int arch_setup_additional_pages(struct linux_binprm *bprm,
>                                        int uses_interp);
> -extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
> -                                             int uses_interp);
> -#define compat_arch_setup_additional_pages compat_arch_setup_additional_pages
> +extern int compat_arch_setup_additional_pages_ia32(struct linux_binprm *bprm,
> +                                                  int uses_interp);
> +extern int compat_arch_setup_additional_pages_x32(struct linux_binprm *bprm,
> +                                                 int uses_interp);
> +
> +#define compat_arch_setup_additional_pages                             \
> +       ((elf_ex->e_machine == EM_X86_64) ?                             \
> +        compat_arch_setup_additional_pages_x32 : compat_arch_setup_additional_pages_ia32)
>

As in the previous patch, can you wire up the new argument for real, please?