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

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Message-ID: <20171018054431.GA597@jagdpanzerIV>
Date:   Wed, 18 Oct 2017 14:44:31 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     "Tobin C. Harding" <me@...in.cc>
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 (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?

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