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

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Message-ID: <CA+rthh-fJSd2j55013_zsKUnW6DEuqSO0tz+zTOF=NEVtMSLNg@mail.gmail.com>
Date:   Tue, 28 Feb 2017 08:15:50 +0100
From:   Mathias Krause <minipli@...glemail.com>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        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-ml <x86@...nel.org>,
        "linux-kernel@...r.kernel.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 14 February 2017 at 22:42, Mathias Krause <minipli@...glemail.com> wrote:
> On 14 February 2017 at 19:13, H. Peter Anvin <hpa@...or.com> wrote:
>> 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.
>
> Indeed. That's why I've separated the removal into an extra patch --
> to make it easier not to take it.
>
>>
>> Nacked-by: H. Peter Anvin <hpa@...or.com>
>
> Do you want me to send the series again without this patch and patch
> #6 (Geert took it already) or are you okay with sorting them out
> yourself?
>

Ping...
Peter, what's your preference here?

Mathias