Openwall GNU/*/Linux - a small security-enhanced Linux distro for servers
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Date: Sat, 7 Oct 2017 17:08:29 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: "Theodore Ts'o" <tytso@....edu>
Cc: "Roberts, William C" <william.c.roberts@...el.com>, "Tobin C. Harding" <me@...in.cc>, Tejun Heo <tj@...nel.org>, 
	Jordan Glover <Golden_Miller83@...tonmail.ch>, Greg KH <gregkh@...uxfoundation.org>, 
	Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>, Ian Campbell <ijc@...lion.org.uk>, 
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, 
	Steven Rostedt <rostedt@...dmis.org>, Chris Fries <cfries@...gle.com>, 
	Dave Weinstein <olorin@...gle.com>
Subject: Re: [RFC V2 0/6] add more kernel pointer filter options

On Sat, Oct 7, 2017 at 4:44 PM, Theodore Ts'o <tytso@....edu> wrote:
>
> Maybe this is overkill, but what about *encrypting* the pointer using
> fixed, per-boot random key?  It would have to be a block crypto
> algorithm, like Tea/XXTea/XXTEA or Speck.  That has all of the
> benefits of hashing, plus if the key is available (only to privileged
> users, of course), then it would be possible to get the pointer for
> debugging purposes.

I doubt it's going to be used enough to be worth it.

So I'd rather just make it a hash that gives you that identity for
people who want it, and then people who actually need the address
would need to decide whether they _really_ need it in the first place,
or whether they would use %lx instead together with stricty security
rules.

I did test the patch I sent out (using jhash - so not a cryptographic
hash, and with a "random value" that was just a constant) just to see
that it doesn't break anything obvious. As expected, it did break
kernel profiling (which uses /proc/kallsyms), and it obviously made
the kernel pointers I'd already found in dmesg be just garbage, but it
didn't seem insurmountable. More like a "with a couple of fixup cases,
it might all work fine".

So I'd be willing to try it for the next merge window, and see if it
causes unexpected problems..

                Linus

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