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

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Date:   Wed, 25 Apr 2018 22:10:42 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        stable@...nel.org, linuxram@...ibm.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>, mpe@...erman.id.au,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>, shuah@...nel.org
Subject: Re: [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC

On Mon, Mar 26, 2018 at 5:27 PM, Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
>
> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> I got a bug report that the following code (roughly) was
> causing a SIGSEGV:
>
>         mprotect(ptr, size, PROT_EXEC);
>         mprotect(ptr, size, PROT_NONE);
>         mprotect(ptr, size, PROT_READ);
>         *ptr = 100;
>
> The problem is hit when the mprotect(PROT_EXEC)
> is implicitly assigned a protection key to the VMA, and made
> that key ACCESS_DENY|WRITE_DENY.  The PROT_NONE mprotect()
> failed to remove the protection key, and the PROT_NONE->
> PROT_READ left the PTE usable, but the pkey still in place
> and left the memory inaccessible.
>
> To fix this, we ensure that we always "override" the pkee
> at mprotect() if the VMA does not have execute-only
> permissions, but the VMA has the execute-only pkey.
>
> We had a check for PROT_READ/WRITE, but it did not work
> for PROT_NONE.  This entirely removes the PROT_* checks,
> which ensures that PROT_NONE now works.
>
> Reported-by: Shakeel Butt <shakeelb@...gle.com>
>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Fixes: 62b5f7d013f ("mm/core, x86/mm/pkeys: Add execute-only protection keys support")

Hi Dave, are you planning to send the next version of this patch or
going with this one?