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Date: Sat, 05 Sep 2020 04:39:57 -0400
From: "Stefan O'Rear" <>
Subject: Re: Bug in mmap_fixed()

On Fri, Sep 4, 2020, at 3:52 PM, Markus Wichmann wrote:
> touch (one byte in front of the buffer). I don't know, can this crash on
> NOMMU systems? I am aware there were systems in the past lacking an MMU,
> but having a memory protection unit. I just don't know if Linux runs on
> any of them.

To answer the other question here, Linux runs on Cortex-M systems and has
code to program the memory protection unit; I was under the impression it could
do so on a per-process basis but I just checked arch/arm/mm/pmsa-v[78].c and it's
configured once at boot time.  There is an ARM FDPIC ABI but it is not implemented
in musl at this time.

Although even without precise bounds you could get a crash later if it overwrites
something important.


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