linux-kernel - Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?

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Message-ID: <CA+55aFzJ+cXgezVu_wU462wCp=pDO_O=M6ShbxJjcuXUNRwEJQ@mail.gmail.com>
Date:	Fri, 18 Dec 2015 13:09:58 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?

On Fri, Dec 18, 2015 at 1:04 PM, Linus Torvalds
<torvalds@...ux-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
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