linux-kernel - Re: [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT

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Message-ID: <aedcb0b6-73f5-f72f-742e-b417131895d3@intel.com>
Date:   Thu, 26 Apr 2018 10:57:31 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ram Pai <linuxram@...ibm.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        shakeelb@...gle.com, stable@...nel.org, tglx@...utronix.de,
        mpe@...erman.id.au, mingo@...nel.org, akpm@...ux-foundation.org,
        shuah@...nel.org
Subject: Re: [PATCH 4/9] x86, pkeys: override pkey when moving away from
 PROT_EXEC

On 04/06/2018 06:09 PM, Ram Pai wrote:
> Well :). my point is add this code and delete the other
> code that you add later in that function.

I don't think I'm understanding what your suggestion was.  I looked at
the code and I honestly do not think I can remove any of it.

For the plain (non-explicit pkey_mprotect()) case, there are exactly
four paths through __arch_override_mprotect_pkey(), resulting in three
different results.

1. New prot==PROT_EXEC, no pkey-exec support -> do not override
2. New prot!=PROT_EXEC, old VMA not PROT_EXEC-> do not override
3. New prot==PROT_EXEC, w/ pkey-exec support -> override to exec pkey
4. New prot!=PROT_EXEC, old VMA is PROT_EXEC -> override to default

I don't see any redundancy there, or any code that we can eliminate or
simplify.  It was simpler before, but that's what where bug was.