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Date: Fri, 18 Dec 2015 13:09:58 -0800
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Subject: Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Oleg Nesterov <oleg@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>
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On Fri, Dec 18, 2015 at 1:04 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> I do wonder if you need an explicit value, though. I think it's
> reasonable to say that PKRU value 0 is special. It's what we'd start
> processes with, and why not just say that it's what we run signal
> handlers in?
>
> Would any other value ever make sense, really?

Ahh. Your point about the PROT_EXEC handling means that maybe we don't
want to default to zero. Maybe we want to make the default PKRU
startup value be 1 instead, enabling access disable key for key 0?

         Linus