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Subject: Re: [PATCH] pkeys: Introduce PKEY_ALLOC_SIGNALINHERIT and change
 signal semantics
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From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <f9f7edc5-6426-91aa-f279-2f9f4671957a@intel.com>
Date: Wed, 2 May 2018 15:32:42 -0700
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To: Andy Lutomirski <luto@kernel.org>
Cc: Florian Weimer <fweimer@redhat.com>, Linux-MM <linux-mm@kvack.org>, Linux API <linux-api@vger.kernel.org>, linux-x86_64@vger.kernel.org, linux-arch <linux-arch@vger.kernel.org>, X86 ML <x86@kernel.org>, linuxram@us.ibm.com

On 05/02/2018 03:22 PM, Andy Lutomirski wrote:
> That library wants other threads, signal handlers, and, in general, the
> whole rest of the process to be restricted, and that library doesn't want
> race conditions.  The problem here is that, to get this right, we either
> need the PKRU modifications to be syscalls or to take locks, and the lock
> approach is going to be fairly gross.

I totally get the idea that a RDPKRU/WRPKRU is non-atomic and that it
can't be mixed with asynchronous WRPKRU's in that thread.

But, where do those come from in this scenario?  I'm not getting the
secondary mechanism is that *makes* them unsafe.