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Date: Mon, 28 May 2018 11:32:13 +0200
From: Salvatore Mesoraca <>
To: Linus Torvalds <>
Cc: Kees Cook <>, 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

2018-05-27 3:33 GMT+02:00 Linus Torvalds <>:
> 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.

Oh, I didn't expect this, interesting...
A configurable LSM is probably the right way to do this.

Thank you for your time,


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