linux-kernel - Re: [PATCH v4] printk: hash addresses printed with %p

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Date:   Wed, 18 Oct 2017 17:04:06 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     kernel-hardening@...ts.openwall.com,
        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 <will.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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] printk: hash addresses printed with %p

On Wed, Oct 18, 2017 at 02:44:31PM +0900, Sergey Senozhatsky wrote:
> On (10/18/17 15:21), Tobin C. Harding wrote:
> [..]
> > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > index 86c3385b9eb3..4609738cd2cd 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -33,6 +33,8 @@
> >  #include <linux/uuid.h>
> >  #include <linux/of.h>
> >  #include <net/addrconf.h>
> > +#include <linux/siphash.h>
> > +#include <linux/spinlock.h>
> >  #ifdef CONFIG_BLOCK
> >  #include <linux/blkdev.h>
> >  #endif
> > @@ -1591,6 +1593,70 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
> >  	return widen_string(buf, buf - buf_start, end, spec);
> >  }
> >  
> > +/* protects ptr_secret and have_key */
> > +DEFINE_SPINLOCK(key_lock);
> > +static siphash_key_t ptr_secret __read_mostly;
> > +static atomic_t have_key = ATOMIC_INIT(0);
> > +
> > +static int initialize_ptr_secret(void)
> > +{
> > +	spin_lock(&key_lock);
> > +	if (atomic_read(&have_key) == 1)
> > +		goto unlock;
> > +
> > +	get_random_bytes(&ptr_secret, sizeof(ptr_secret));
> > +	atomic_set(&have_key, 1);
> > +
> > +unlock:
> > +	spin_unlock(&key_lock);
> > +	return 0;
> > +}
> 
> is this spinlock legal? what happens if we are getting interrupted by NMI?

I think we can do without the spinlock. I think I was already told that when
I tried to put it [some where else] in v1.

It's fun failing in public ;)

> printk()
>  vprintk_emit()
>   vscnprintf()
>    pointer()
>     ptr_to_id()
>      initialize_ptr_secret()
>       spin_lock(&key_lock)
> 
> ----> NMI
> 
>       printk()
>        printk_safe_log_store()
>         vscnprintf()
>          pointer()
>           ptr_to_id()
>            initialize_ptr_secret()
>             spin_lock(&key_lock)   <<<<
> 
> 
> or am I completely misreading the patch? sorry if so.
> 
> 	-ss

thanks,
Tobin.