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

Steven Rostedt
2018-04-27T02:48:29Z

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

> On Thu, 26 Apr 2018 21:13:51 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > On Thu, 26 Apr 2018 17:10:03 +0900
> > Masami Hiramatsu <mhiramat@kernel.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