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Date: Tue, 24 Nov 2015 16:44:07 -0800
From: Kees Cook <>
To: Andy Lutomirski <>
Cc: linux-arch <>, Thomas Gleixner <>, 
	Ingo Molnar <>, 
	"" <>, 
	"" <>, Arnd Bergmann <>, 
	X86 ML <>, "H. Peter Anvin" <>, Michael Ellerman <>
Subject: Re: [PATCH 1/2] x86: introduce post-init read-only memory

On Tue, Nov 24, 2015 at 4:34 PM, Andy Lutomirski <> wrote:
> On Nov 24, 2015 1:38 PM, "Kees Cook" <> wrote:
>> One of the easiest ways to protect the kernel from attack is to reduce
>> the internal attack surface exposed when a "write" flaw is available. By
>> making as much of the kernel read-only as possible, we reduce the
>> attack surface.
>> Many things are written to only during __init, and never changed
>> again. These cannot be made "const" since the compiler will do the wrong
>> thing (we do actually need to write to them). Instead, move these items
>> into a memory region that will be made read-only during mark_rodata_ro()
>> which happens after all kernel __init code has finished.
>> This introduces __read_only as a way to mark such memory, and adds some
>> documentation about the existing __read_mostly marking.
> Obligatory bikeshed:  __ro_after_init, please.  It's barely longer,
> and it directly explains what's going on.  __read_only makes me think
> that it's really read-only and could, for example, actually be in ROM.

I'm fine with that. Anyone else want to chime in before I send a v2?


Kees Cook
Chrome OS & Brillo Security

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