linux-kernel - Re: [PATCH 00/12] [RFC] x86: Memory Protection Keys

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Message-ID: <20150507201843.0ccf0938@lxorguk.ukuu.org.uk>
Date:	Thu, 7 May 2015 20:18:43 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Dave Hansen <dave@...1.net>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH 00/12] [RFC] x86: Memory Protection Keys

> Data structures like logs or journals that are only written to in very
> limited code paths, but that you want to protect from "stray" writes.

Anything with lots of data where you want to minimise the risk of stray
accesses even if just as a debug aid (consider things like memcached).
> 
> Maybe even a database where a query operation will never need to write
> to memory, but an insert would.  You could keep the data R/O during the
> entire operation except when an insert is actually in progress.  It
> narrows the window where data might be corrupted.  This becomes even
> more valuable if a stray write to memory is guaranteed to hit storage...
> like with persistent memory.
> 
> Someone mentioned to me that valgrind does lots of mprotect()s and might
> benefit from this.

You can also use it for certain types of emulator trickery, and I suspect
even for things like interpreters and controlling access to "tainted"
values.

Other obvious uses are making it a shade harder for SSL or ssh type
errors to leak things like key data by reducing the damage done by out of
bound accesses.

> We could keep heap metadata as R/O and only make it R/W inside of
> malloc() itself to catch corruption more quickly.

If you implement multiple malloc pools you can chop up lots of stuff.

In library land it isn't just stuff like malloc, you can use it as
a debug weapon to protect library private data from naughty application
code.

There are some other debug uses when catching faults - fast ways to do
range access breakpoints for example.

Alan
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