kernel-hardening - Re: [PATCH v7] printk: hash addresses printed with %p

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Message-ID: <20171030212428.GR12341@eros>
Date: Tue, 31 Oct 2017 08:24:28 +1100
From: "Tobin C. Harding" <me@...in.cc>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
	kernel-hardening@...ts.openwall.com, Theodore Ts'o <tytso@....edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Tycho Andersen <tycho@...ker.com>,
	"Roberts, William C" <william.c.roberts@...el.com>,
	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>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <wilal.deacon@....com>, Chris Fries <cfries@...gle.com>,
	Dave Weinstein <olorin@...gle.com>,
	Daniel Micay <danielmicay@...il.com>,
	Djalal Harouni <tixxdz@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7] printk: hash addresses printed with %p

On Mon, Oct 30, 2017 at 04:22:44PM -0400, Steven Rostedt wrote:
> On Wed, 25 Oct 2017 14:49:34 +1100
> "Tobin C. Harding" <me@...in.cc> wrote:
> > 
> > First, the static_key stuff.
> > 
> > DEFINE_STATIC_KEY_TRUE(no_ptr_secret) : Doesn't sleep, just a
> > declaration. 
> > 
> > if (static_branch_unlikely(&no_ptr_secret)) {} : Doesn't sleep, just
> > some assembler to jump to returning true or false.
> > 
> > static_branch_disable(&no_ptr_secret) : Doesn't sleep, just atomic read
> > and set and maybe a WARN_ONCE.
> 
> How quickly do you need static_branch_disable() executed? You could
> always pass the work off to a worker thread (that can schedule).
> 
> random_ready_callback -> initiates worker thread -> enables the static branch
> 
> -- Steve

thanks Steve, v8 and onward does away with the static branch and uses a
global boolean instead.

thanks,
Tobin.

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