linux-kernel - Re: [PATCH 3/6] x86/cpu: proc - remove "wp" status line in cpuinfo

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Date:   Tue, 14 Feb 2017 10:13:22 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Mathias Krause <minipli@...glemail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jesper Nilsson <jesper.nilsson@...s.com>,
        Mikael Starvik <starvik@...s.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 3/6] x86/cpu: proc - remove "wp" status line in cpuinfo

On 02/12/17 13:12, Mathias Krause wrote:
> As of commit a5c2a893dbd4 ("x86, 386 removal: Remove
> CONFIG_X86_WP_WORKS_OK") the kernel won't boot if CR0.WP isn't working
> correctly. This makes a process reading this file always see "wp : yes"
> here -- otherwise there would be no process to begin with ;)
> 
> As this status line in /proc/cpuinfo serves no purpose for quite some
> time now, get rid of it.
> 
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: H. Peter Anvin <hpa@...ux.intel.com>
> Signed-off-by: Mathias Krause <minipli@...glemail.com>
> ---
>  arch/x86/kernel/cpu/proc.c |    6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index 6df621ae62a7..c6c5217a7980 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -30,8 +30,7 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
>  		   "coma_bug\t: %s\n"
>  		   "fpu\t\t: %s\n"
>  		   "fpu_exception\t: %s\n"
> -		   "cpuid level\t: %d\n"
> -		   "wp\t\t: yes\n",
> +		   "cpuid level\t: %d\n",
>  		   static_cpu_has_bug(X86_BUG_FDIV) ? "yes" : "no",
>  		   static_cpu_has_bug(X86_BUG_F00F) ? "yes" : "no",
>  		   static_cpu_has_bug(X86_BUG_COMA) ? "yes" : "no",
> @@ -45,8 +44,7 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
>  	seq_printf(m,
>  		   "fpu\t\t: yes\n"
>  		   "fpu_exception\t: yes\n"
> -		   "cpuid level\t: %d\n"
> -		   "wp\t\t: yes\n",
> +		   "cpuid level\t: %d\n",
>  		   c->cpuid_level);
>  }
>  #endif
> 

Potential userspace breakage, which is why the line was left in the
first place despite its value now being hard-coded.  Removing it will
save a whopping 9 bytes of kernel rodata; this is a very small price to
pay for guaranteeing continued compatibility.

Nacked-by: H. Peter Anvin <hpa@...or.com>