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Date: Thu, 19 Oct 2017 07:49:06 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: "Tobin C. Harding" <me@...in.cc>
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
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);
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