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From: Andy Lutomirski <luto@amacapital.net>
Date: Wed, 02 May 2018 21:18:11 +0000
Message-ID: <CALCETrUfO=vXg5rT-n=y8pLktcq5+ORvgpsOXCHG4GaugB3k2A@mail.gmail.com>
Subject: Re: [PATCH] pkeys: Introduce PKEY_ALLOC_SIGNALINHERIT and change
 signal semantics
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To: linuxram@us.ibm.com
Cc: Florian Weimer <fweimer@redhat.com>, Dave Hansen <dave.hansen@intel.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>

On Wed, May 2, 2018 at 2:13 PM Ram Pai <linuxram@us.ibm.com> wrote:


> > Ram, would you please comment?

> on POWER the pkey behavior will remain the same at entry or at exit from
> the signal handler.  For eg:  if a key is read-disabled on entry into
> the signal handler, and gets read-enabled in the signal handler, than it
> will continue to be read-enabled on return from the signal handler.

> In other words, changes to key permissions persist across signal
> boundaries.

I don't know about POWER's ISA, but this is crappy behavior.  If a thread
temporarily grants itself access to a restrictive memory key and then gets
a signal, the signal handler should *not* have access to that key.