linux-kernel - Re: [PATCH tip/core/rcu 02/20] torture: Prepare scripting for shift from %p to %pK

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Date:   Sun, 10 Dec 2017 12:39:11 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        David Laight <David.Laight@...lab.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "jiangshanlai@...il.com" <jiangshanlai@...il.com>,
        "dipankar@...ibm.com" <dipankar@...ibm.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mathieu.desnoyers@...icios.com" <mathieu.desnoyers@...icios.com>,
        "josh@...htriplett.org" <josh@...htriplett.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "fweisbec@...il.com" <fweisbec@...il.com>,
        "oleg@...hat.com" <oleg@...hat.com>
Subject: Re: [PATCH tip/core/rcu 02/20] torture: Prepare scripting for shift
 from %p to %pK

On Sun, Dec 10, 2017 at 4:52 AM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>>
>>> Perhaps it should have printed a fixed, non-zero value for non-zero
>>> pointers.
>>
>> I must leave this to the people who have a dog in that contest.  ;-)
>
> Since there is an ongoing discussion with security people near to %pK
> and alike, I added Kees and Linus to Cc list.
>
> The proposed change can be done easily, though I have no knowledge
> about possible implications.

I'd rather make %pK act more like %p than have gratuitous differences.

I also think %pK is kind of pointless in general. It has not been a
big success, and the whole "root or not" is kind of nasty anyway. Root
in a container? Things like that.

So I think that if people worry  about leaking pointers, they should
primarily go for:

 - just use %p and now get the hashed value

 - if the hashed value is pointless, ask yourself whether the pointer
itself is important. Maybe it should be removed?

 - as a last option, if you really  think the true pointer value is
important, why is root so special, and maybe you should use %px and
make sure you have proper sensible permissions.

..and %pK just isn't really the answer in any of those cases.

         Linus