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Date: Sat, 26 May 2018 18:33:23 -0700
From: Linus Torvalds <>
To: Kees Cook <>
Cc: Salvatore Mesoraca <>, Jann Horn <>, 
	Kernel Hardening <>, 
	LSM List <>, 
	Linux Kernel Mailing List <>, linux-mm <>, 
	Andrew Morton <>, Alexey Dobriyan <>, 
	Akinobu Mita <>, Dmitry Vyukov <>, 
	Arnd Bergmann <>, Davidlohr Bueso <>
Subject: Re: [PATCH] proc: prevent a task from writing on its own /proc/*/mem

On Sat, May 26, 2018 at 5:32 PM Kees Cook <> wrote:

> I went through some old threads from 2012 when e268337dfe26 was
> introduced, and later when things got looked at during DirtyCOW. There
> was discussion about removing FOLL_FORCE (in order to block writes on
> a read-only memory region).

Side note, we did that for /dev/mem, and things broke.

Thus commit f511c0b17b08 "Yes, people use FOLL_FORCE ;)"

Side note, that very sam ecommit f511c0b17b08 is also the explanation for
why the patch under discussion now seems broken.

People really do use "write to /proc/self/mem" as a way to keep the
mappings read-only, but have a way to change them when required.


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