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

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Message-ID: <CA+55aFxLUqiT2o6G-eSaGz1=o765U78Sxvrpx+5Y1Fk=Siei=Q@mail.gmail.com>
Date:	Fri, 18 Dec 2015 15:20:18 -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 3:16 PM, Andy Lutomirski <luto@...capital.net> wrote:
>
> Yes, I think.  If I'm using protection keys to protect some critical
> data structure (important stuff in shared memory, important memory
> mapped files, pmem, etc), then I'll allocate a protection key and set
> PKRU to deny writes.  The problem is that I really, really want writes
> denied except when explicitly enabled in narrow regions of code that
> use wrpkru to enable them, and I don't want an asynchronous signal
> delivered in those narrow regions of code or newly cloned threads to
> pick up the write-allow value.  So I want baseline_pkru to have the
> deny writes entry.

Hmm. Ok, that does sound like a valid and interesting usage case. Fair enough.

                Linus
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