linux-kernel - Re: [PATCH 1/3] arm64:add missing CONFIG_STRICT_KERNEL_RWX for mark_rodata

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Message-ID: <20180530080816.f74elebj4demiohl@salmiak>
Date:   Wed, 30 May 2018 09:08:16 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Nixiaoming <nixiaoming@...wei.com>
Cc:     Will Deacon <will.deacon@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "marc.zyngier@....com" <marc.zyngier@....com>,
        "james.morse@....com" <james.morse@....com>,
        "kristina.martsenko@....com" <kristina.martsenko@....com>,
        "steve.capper@....com" <steve.capper@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "zhang.jia@...ux.alibaba.com" <zhang.jia@...ux.alibaba.com>,
        "schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
        "heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>
Subject: Re: [PATCH 1/3] arm64:add missing CONFIG_STRICT_KERNEL_RWX for
 mark_rodata_ro

On Wed, May 30, 2018 at 03:31:38AM +0000, Nixiaoming wrote:
> Unable to set CONFIG_STRICT_KERNEL_RWX=n by make menuconfig ARCH=arm64

Indeed. Making this mandatory was a deliberate decision, in part because this
allows simplification of code (e.g. removal of #ifdef guards).

> When reading the code, I feel it is more appropriate to add macro control
> here.

I must disagree. I do not think it makes sense to add an #ifdef for a
configuration option that is mandatory.

There are other places in the kernel that should behave differently if
CONFIG_STRICT_KERNEL_RWX were disabled, so this wouldn't be sufficient even if
we were to make CONFIG_STRICT_KERNEL_RWX optional. i.e. the #ifdef would give
the misleading impression that STRICT_KERNEL_RWX *could* be made optional, even
though this might not function correctly.

Having an #ifdef here makes the code more complicated and confusing, for the
benefit of a case which cannot occur.

Thanks,
Mark.

> -----Original Message-----
> From: Will Deacon [mailto:will.deacon@....com] 
> Sent: Tuesday, May 29, 2018 11:45 PM
> To: Nixiaoming <nixiaoming@...wei.com>
> Cc: catalin.marinas@....com; ard.biesheuvel@...aro.org; marc.zyngier@....com; james.morse@....com; kristina.martsenko@....com; steve.capper@....com; tglx@...utronix.de; mingo@...hat.com; hpa@...or.com; akpm@...ux-foundation.org; vbabka@...e.cz; mhocko@...e.com; dave.hansen@...ux.intel.com; dan.j.williams@...el.com; kirill.shutemov@...ux.intel.com; zhang.jia@...ux.alibaba.com; schwidefsky@...ibm.com; heiko.carstens@...ibm.com; gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; x86@...nel.org; linux-s390@...r.kernel.org
> Subject: Re: [PATCH 1/3] arm64:add missing CONFIG_STRICT_KERNEL_RWX for mark_rodata_ro
> 
> On Tue, May 29, 2018 at 09:36:15PM +0800, nixiaoming wrote:
> > mark_rodata_ro is only called by the function mark_readonly when
> > CONFIG_STRICT_KERNEL_RWX=y,
> > if CONFIG_STRICT_KERNEL_RWX is not set
> > a compile warning may be triggered: unused function
> 
> How are you achieving this configuration? In our Kconfig we select this
> unconditionally.
> 
> Will