linux-kernel - Re: [PATCH] x86/refcount: Implement fast refcount

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Message-ID: <CAGXu5jLK9YwgaPSyykGoyXD1Ls=yZZ7b76Lns6pZY2+dpP+05w@mail.gmail.com>
Date:   Mon, 24 Apr 2017 13:21:38 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Eric Biggers <ebiggers3@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>,
        "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jann Horn <jann@...jh.net>,
        "David S. Miller" <davem@...emloft.net>,
        linux-arch <linux-arch@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        PaX Team <pageexec@...email.hu>
Subject: Re: [PATCH] x86/refcount: Implement fast refcount_t handling

On Mon, Apr 24, 2017 at 3:48 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Apr 21, 2017 at 03:09:39PM -0700, Kees Cook wrote:
>> diff --git a/drivers/misc/lkdtm_bugs.c b/drivers/misc/lkdtm_bugs.c
>> index e3f4cd8876b5..1bdafb29b802 100644
>> --- a/drivers/misc/lkdtm_bugs.c
>> +++ b/drivers/misc/lkdtm_bugs.c
>> @@ -135,9 +135,15 @@ void lkdtm_HUNG_TASK(void)
>>       schedule();
>>  }
>>
>> +#ifdef CONFIG_FAST_REFCOUNT
>> +#define REFCOUNT_MAX INT_MAX
>> +#else
>> +#define REFCOUNT_MAX UINT_MAX
>> +#endif
>
> That doesn't seem like a sensible place for this.

I'll drop the LKDTM changes from this particular patch. As for the
define, I think it's only interesting to LKDTM since it's the only
part interested in refcount_t internals. (i.e. nothing else would (or
should) use this information.)

-Kees

-- 
Kees Cook
Pixel Security