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Date: Fri, 18 Dec 2015 15:20:18 -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 3:16 PM, Andy Lutomirski <luto@amacapital.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