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

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Message-ID: <CA+55aFwU7cjSTB3Yk7S1Bcfo244WS9cm==WXZZcN3ZAs+J2jug@mail.gmail.com>
Date:	Fri, 18 Dec 2015 15:08:50 -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 2:28 PM, Andy Lutomirski <luto@...capital.net> wrote:
>
> Apps that don't want to use the baseline_pkru mechanism could use
> syscalls to claim ownership of protection keys but then manage them
> purely with WRPKRU directly.  We could optionally disallow
> mprotect_key on keys that weren't allocated in advance.
>
> Does that seem sane?

So everything seems sane except for the need for that baseline_pkru.

I'm not seeing why it couldn't just be a fixed value. Is there any
real downside to it?

                    Linus
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