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

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Date:	Thu, 7 May 2015 21:26:20 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	Dave Hansen <dave@...1.net>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH 00/12] [RFC] x86: Memory Protection Keys

* One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk> wrote:

> > 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.

I'd say that a 64-bit address space is large enough to hide buffers in 
from accidental corruption, without any runtime page protection 
flipping overhead?

> 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.

I think libraries are happy enough to work without bugs - apps digging 
around in library data are in a "you keep all the broken pieces" 
situation, why would a library want to slow down every good citizen 
down with extra protection flipping/unflipping accesses?

The Valgrind usecase looks somewhat legit, albeit not necessarily for 
multithreaded apps: there you generally really want protection changes 
to be globally visible, such as publishing the effects of free() or 
malloc().

Also, will apps/libraries bother if it's not a standard API and if it 
only runs on very fresh CPUs?

Thanks,

	Ingo
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