linux-hardening - Re: [PATCH v4 22/26] arm64: mm: move ro_after

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Message-ID: <202206160917.D7DB8221@keescook>
Date:   Thu, 16 Jun 2022 09:18:13 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-hardening@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Brown <broonie@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: Re: [PATCH v4 22/26] arm64: mm: move ro_after_init section into the
 data segment

On Thu, Jun 16, 2022 at 01:31:23PM +0200, Ard Biesheuvel wrote:
> We used to have
> 
> text
> --
> rodata
> (ro_after_init)
> --
> inittext
> --
> initdata
> --
> data
> bss
> 
> where -- are the segment boundaries, which are always aligned to 64k on arm64
> 
> After this patch, we get
> 
> text
> --
> rodata
> --
> inittext
> --
> initdata
> --
> (ro_after_init)
> data
> bss
> 
> so in terms of padding due to alignment, there is not a lot of difference.

But how is ro_after_init read-only and data isn't, if there isn't a
segment alignment to make that work out?

-- 
Kees Cook