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Message-ID: <20171022233216.GM29874@eros>
Date: Mon, 23 Oct 2017 10:32:16 +1100
From: "Tobin C. Harding" <me@...in.cc>
To: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.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>,
Steven Rostedt <rostedt@...dmis.org>,
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 v5] printk: hash addresses printed with %p
On Thu, Oct 19, 2017 at 07:49:06AM +0200, Jason A. Donenfeld wrote:
> A small detail carried over from the other thread:
>
> >
> > but a bigger problem might the following thing:
> >
> > vscnprintf()
> > pointer()
> > ptr_to_id()
> > initialize_ptr_secret()
> > get_random_bytes()
> > _get_random_bytes()
> > extract_crng()
> > _extract_crng()
> > spin_lock_irqsave(&crng->lock, flags); <<<<<
> >
> >
> > this, once again, can deadlock. can it? just like before:
>
> So, actually, then, we need to do this as an initcall. Fortunately,
> that simplifies things greatly. Here's a rough sketch of what that
> looks like, which you'll probably need to debug and refine:
>
>
>
> static siphash_key_t ptr_secret __ro_after_init;
> static DEFINE_STATIC_KEY_TRUE(no_ptr_secret);
>
> static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
> {
> if (static_branch_unlikely(&no_ptr_secret))
> return "(pointer value)";
>
> hashval = ....
>
> }
>
> static void fill_random_ptr_key(struct random_ready_callback *rdy)
> {
> get_random_bytes(&ptr_secret, sizeof(ptr_secret));
> static_branch_disable(&no_ptr_secret);
> }
>
> static struct random_ready_callback random_ready = {
> .func = fill_random_ptr_key
> };
>
> static int __init initialize_ptr_random(void)
> {
> int ret = add_random_ready_callback(&random_ready);
>
> if (!ret)
> return 0;
> else if (ret == -EALREADY) {
> fill_random_ptr_key(&random_ready);
> return 0;
> }
>
> return ret;
> }
> early_initcall(initialize_ptr_random);
Thanks for this Jason. This is _conceptually_ what I wanted since before v1, I obviously did not ask
the right questions. Not to worry, we got there in the end. The process works, thanks to every
bodies patience :)
Implemented for v6 as suggested (including __read_mostly), you even got it fast for the usual
case. Thanks, I learned a whole bunch from this email.
Tobin.
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