linux-kernel - Re: [PATCH 3/6] x86/dumpstack: make printk_stack

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160824192445.tiftvwceupuixays@treble>
Date:   Wed, 24 Aug 2016 14:24:45 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH 3/6] x86/dumpstack: make printk_stack_address() more
 generally useful

On Wed, Aug 24, 2016 at 12:07:06PM -0700, Joe Perches wrote:
> On Wed, 2016-08-24 at 13:43 -0500, Josh Poimboeuf wrote:
> > On Wed, Aug 24, 2016 at 10:28:38AM -0700, Joe Perches wrote:
> > > On Wed, 2016-08-24 at 11:50 -0500, Josh Poimboeuf wrote:
> > > > Change printk_stack_address() to be useful when called by an unwinder
> > > > outside the context of dump_trace().
> > > > 
> > > > Specifically:
> > > > 
> > > > - printk_stack_address()'s 'data' argument is always used as the log
> > > >   level string.  Make that explicit.
> []
> > > If this is true, and I'm not sure it is as I believe
> > > there are static strings emitted like EOE and IRQ,
> > > shouldn't this bubble up through the calling tree?
> 
> > []
> > This function needs to keep its 'void *data' argument because it's a
> > callback for stacktrace_ops, so it has to conform to the callback
> > interface.  'data' is used for passing a pointer to an opaque data
> > structure to the callback.
> > 
> > Also this is the only caller of printk_stack_address(), so there's
> > nowhere else to bubble it up to.
> 
> And that shows that print_stack_address(data is not always a log level.
> ie: walk_stack uses it to print a string not a log level.

Hm, can you be more specific?  As far as I can tell, here's the only
possible call path to print_trace_address() and printk_stack_address():

show_trace_log_lvl()
  dump_trace()				// ops is print_trace_op
    print_context_stack()		// ops->walk_stack
      print_trace_address()		// ops->address
          printk_stack_address()

So 'data' is a sneaky way to pass 'log_lvl' from show_trace_log_lvl() to
print_trace_address(), without dump_trace() and print_context_stack()
knowing what it is, because they're used in other places where 'data'
means something else.

-- 
Josh