linux-kernel - Re: [PATCH -tip v2 4/7] kprobes: Replace %p with other pointer types

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Date:   Thu, 26 Apr 2018 22:48:24 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Ananth N Mavinakayanahalli <ananth@...ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jon Medhurst <tixy@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "Tobin C . Harding" <me@...in.cc>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        akpm@...ux-foundation.org, acme@...nel.org,
        brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        stable@...r.kernel.org
Subject: Re: [PATCH -tip v2 4/7] kprobes: Replace %p with other pointer
 types

On Fri, 27 Apr 2018 11:39:51 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Thu, 26 Apr 2018 21:13:51 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Thu, 26 Apr 2018 17:10:03 +0900
> > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >   
> > > Replace %p with appropriate pointer types (or just remove it)
> > >  - Use %pS if possible
> > >  - Use %px only for the function right before BUG().
> > >  - Remove unneeded error message.  
> > 
> > I'm not sure "right before BUG()" is legitimate for using %px. Why not
> > still use %pS?  
> 
> Since BUG() will dump all registers and stacks which includes
> raw address information and reboot the system (means reset the
> kaslr base offset), I thought it may not add additional damage.

BUG() has been changed to print out %pS and not the address while doing
the stack dump. It only prints the address if it doesn't find a
function name. For example:

CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.11.0-rc3-test+ #48
Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 02/22/2014
Call Trace:
 dump_stack+0x68/0x92
 lockdep_rcu_suspicious+0xf7/0x100
 rcu_read_lock+0x5f/0x61
 __is_insn_slot_addr+0x23/0x5c
 __kernel_text_address+0x4a/0x80
 show_trace_log_lvl+0x157/0x296
 ? module_assert_mutex_or_preempt+0x4f/0x51
 show_stack+0x3d/0x3f
 dump_stack+0x68/0x92
 __warn+0xc2/0xdd
 ? 0xffffffffa0026077
 warn_slowpath_null+0x1d/0x1f
 module_assert_mutex_or_preempt+0x4f/0x51
 __module_address+0x2a/0xac
 ? 0xffffffffa0026077
 __module_text_address+0x12/0x59
 ? 0xffffffffa0026077
 is_module_text_address+0xe/0x16
 __kernel_text_address+0x2b/0x80
 ? 0xffffffffa0026077
 unwind_get_return_address+0x50/0x5c

> 
> Anyway, for this patch we can use %pS. For the next [5/7] patch,
> I'm not sure %pS is good for dumping a stack address...

Although it now is.

-- Steve