linux-kernel - Re: [RFC PATCH 7/7 v1]powerpc: Deliver SEGV signal on protection key violation.

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Message-ID: <1497653684.2897.104.camel@kernel.crashing.org>
Date:   Sat, 17 Jun 2017 08:54:44 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Ram Pai <linuxram@...ibm.com>
Cc:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, paulus@...ba.org,
        aneesh.kumar@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH 7/7 v1]powerpc: Deliver SEGV signal on protection
 key violation.

On Fri, 2017-06-16 at 12:15 -0700, Ram Pai wrote:
> gp_regs size is not changed, nor is the layout. A unused field in
> the gp_regs is used to fill in the AMR contents. Old binaries will not
> be knowing about this unused field, and hence should not break.
> 
> New binaries can leverage this already existing but newly defined
> field; to read the contents of AMR.
> 
> Is it still a concern?

Calls to sys_swapcontext with a made-up context will end up with a crap
AMR if done by code who didn't know about that register.

Ben.