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

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Message-ID: <6adeb081-33d9-47f5-b812-e867561e0ded@suse.com>
Date:   Thu, 30 Nov 2023 18:04:20 +0200
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     Borislav Petkov <bp@...en8.de>, X86 ML <x86@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/ia32: State that IA32 emulation is disabled



On 30.11.23 г. 17:52 ч., Borislav Petkov wrote:
> From: "Borislav Petkov (AMD)" <bp@...en8.de>
> 
> 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@...en8.de>
> Cc: Nikolay Borisov <nik.borisov@...e.com>
> ---
>   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 */