Re: [PATCH] pkeys: Introduce PKEY_ALLOC_SIGNALINHERIT and change signal semantics

On Wed, May 02, 2018 at 09:18:11PM +0000, Andy Lutomirski wrote:

On Wed, May 2, 2018 at 2:13 PM Ram Pai [off-list ref] wrote:

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Ram, would you please comment?

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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.

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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.

This is a new requirement that I was not aware off. Its not documented
anywhere AFAICT.  Regardless of how the ISA behaves, its still a kernel
behavior that needs to be clearly defined.

-- 
Ram Pai