Re: [PATCH] x86/ia32: State that IA32 emulation is disabled

[Nikolay Borisov]

On 30.11.23 г. 17:52 ч., Borislav Petkov wrote:
> From: "Borislav Petkov (AMD)" <bp@xxxxxxxxx>
>
> Issue a short message once, on the first try to load a 32-bit process to
> save people time when wondering why it won't load and says:
>
>    -bash: ./strsep32: cannot execute binary file: Exec format error
>
> No functional changes.
>
> Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
> Cc: Nikolay Borisov <nik.borisov@xxxxxxxx>
> ---
>   arch/x86/include/asm/elf.h  | 2 +-
>   arch/x86/include/asm/ia32.h | 9 ++++++++-
>   2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> index a0234dfd1031..1e16bd5ac781 100644
> --- a/arch/x86/include/asm/elf.h
> +++ b/arch/x86/include/asm/elf.h
> @@ -150,7 +150,7 @@ do {						\
>   	((x)->e_machine == EM_X86_64)
>   
>   #define compat_elf_check_arch(x)					\
> -	((elf_check_arch_ia32(x) && ia32_enabled()) ||			\
> +	((elf_check_arch_ia32(x) && ia32_enabled_verbose()) ||		\
>   	 (IS_ENABLED(CONFIG_X86_X32_ABI) && (x)->e_machine == EM_X86_64))
>   
>   static inline void elf_common_init(struct thread_struct *t,
> diff --git a/arch/x86/include/asm/ia32.h b/arch/x86/include/asm/ia32.h
> index 5a2ae24b1204..43e02b52ad19 100644
> --- a/arch/x86/include/asm/ia32.h
> +++ b/arch/x86/include/asm/ia32.h
> @@ -2,7 +2,6 @@
>   #ifndef _ASM_X86_IA32_H
>   #define _ASM_X86_IA32_H
>   
> -
>   #ifdef CONFIG_IA32_EMULATION
>   
>   #include <linux/compat.h>
> @@ -84,4 +83,12 @@ static inline bool ia32_enabled(void)
>   
>   #endif
>   
> +static inline bool ia32_enabled_verbose(void)
> +{
> +#ifdef CONFIG_IA32_EMULATION
> +	pr_notice_once("32-bit emulation disabled. You can reenable with ia32_emulation=on\n");

	Actually this will result in a false-positive, even with the 
DEFAULT_DISABLED but booting with ia32_emulation = 0 so it's best if 
it's predicated on the output of ia32_enabled. This means we'll always 
pay the price of the branch even if it's disabled but removes a spurious 
notice in a certain case.

> +#endif
> +	return ia32_enabled();
> +}
> +
>   #endif /* _ASM_X86_IA32_H */