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Re: [Qemu-devel] [PATCH 11/13] tests/vm: netbsd autoinstall, using seria

From: Kamil Rytarowski
Subject: Re: [Qemu-devel] [PATCH 11/13] tests/vm: netbsd autoinstall, using serial console
Date: Thu, 9 May 2019 21:07:07 +0200
User-agent: Mozilla/5.0 (X11; NetBSD amd64; rv:60.0) Gecko/20100101 Thunderbird/60.6.0

On 09.05.2019 18:39, Richard Henderson wrote:
> On 5/8/19 11:47 PM, Gerd Hoffmann wrote:
>> So, from looking at the patch it seems you need two mappings of the same
>> page, one writable and one executable.
>> Or, maybe it is also possible with one mapping which is writable first
>> when you fill it with code, then gets flipped over to executable when
>> you are done with the initialization and want use it.
>> Is that correct?
> That's certainly the way I read that patch.
>> I suspect supporting that in tcg isn't exactly trivial.
> It shouldn't be too hard, if required.  All of the writing to the buffer is
> isolated to a couple of inline functions.
> I do wonder if using paxctl -m as a part of the build process for affected 
> *BSD
> isn't just as easy?

paxctl(8) is available only for NetBSD.

paxctl(8) is the last resort solution and shall be avoided due to a
security risk.

Only few exceptions shall be allowed to switch mapping protection or
request RWX mappings (mainly JIT and a process running under a debugger).

> r~

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