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

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Message-ID: <CA+55aFz9XdUP0BQXuq7UuZT1ke-+JVThs-bssMi2sV2xLubHVg@mail.gmail.com>
Date:	Fri, 18 Dec 2015 13:04:27 -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 12:49 PM, Andy Lutomirski <luto@...capital.net> wrote:
>
> IOW, I like my idea in which signal delivery always sets PKRU to the
> application-requested-by-syscall values and sigreturn restores it.

So I don't mind that, as long as the whole "sigreturn restores it" is
part of things.

Your original email with the suggestion to *not* resture PKRU I didn't
like. Setting it and restoring it is fine.

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?

                 Linus
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