linux-kernel - Re: [PATCH v2] tracing, printk: Force no hashing when trace

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Date:   Tue, 3 Apr 2018 18:03:13 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Tobin C. Harding" <me@...in.cc>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Laight <David.Laight@...lab.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH v2] tracing, printk: Force no hashing when
 trace_printk() is used

On Tue, 3 Apr 2018 14:43:43 -0700
Kees Cook <keescook@...omium.org> wrote:

> > A static_key is added called "trace_debug" and if it is set, then %p will
> > not be hashed.  
> 
> Hrm, well, using a static key does make it weirder for an attacker to enable. :)

Not just weirder, much more difficult. static_keys are read only (code
segments). To enable them, the system makes the code portion rw updates
the code, then sets it back to ro.

> 
> Whatever the case, if you can get Linus's Ack, sure. I would expect

Linus you OK with this?

> he'd want you to change all the trace_printk()s to %px with
> justifications, though.

What trace_printk()s do you want to change? They are throw away
functions. trace_printk() is not something that stays in the kernel.
It's added during debugging and then removed before submitting what you
are working on upstream. It's just annoying to have to use %px instead
of %p when debugging.

-- Steve