Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1420442

Re: [PATCH tip/master] [BUGFIX] kprobes/x86: Fix to clear TF bit in fault-on-single-stepping

Show all headers | View raw

On Sat, Jun 11, 2016 at 11:06:53PM +0900, Masami Hiramatsu wrote:
> Fix kprobe_fault_handler to clear TF (trap flag) bit of
> flags register in the case of fault fixup on single-stepping.
> 
> If we put a kprobe on the instruction which can cause a
> page fault (e.g. actual mov instructions in copy_user_*),
> that fault happens on a single-stepping buffer. In this
> case, kprobes resets running instance so that the CPU can
> retry execution on the original ip address.
> However, current code forgets reset TF bit. Since this
> fault happens with TF bit set for enabling single-stepping,
> when it retries, it causes a debug exception and kprobes
> can not handle it because it already reset itself.
> 
> On the most of x86-64 platform, it can be easily reproduced
> by using kprobe tracer. E.g.
> 
>   # cd /sys/kernel/debug/tracing
>   # echo p copy_user_enhanced_fast_string+5 > kprobe_events
>   # echo 1 > events/kprobes/enable
> 
> And you'll see a kernel panic on do_debug(), since the debug
> trap is not handled by kprobes.
> 
> To fix this problem, we just need to clear the TF bit when
> resetting running kprobe.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>

Good catch!

Reviewed-by: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH tip/master] [BUGFIX] kprobes/x86: Fix to clear TF bit in fault-on-single-stepping Masami Hiramatsu <mhiramat@kernel.org> - 2016-06-11 16:10 +0200
  Re: [PATCH tip/master] [BUGFIX] kprobes/x86: Fix to clear TF bit in  fault-on-single-stepping Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com> - 2016-06-13 06:40 +0200
  Re: [PATCH tip/master] [BUGFIX] kprobes/x86: Fix to clear TF bit in  fault-on-single-stepping Steven Rostedt <rostedt@goodmis.org> - 2016-06-14 01:20 +0200
    Re: [PATCH tip/master] [BUGFIX] kprobes/x86: Fix to clear TF bit in  fault-on-single-stepping Steven Rostedt <rostedt@goodmis.org> - 2016-06-14 01:30 +0200
      Re: [PATCH tip/master] [BUGFIX] kprobes/x86: Fix to clear TF bit in  fault-on-single-stepping Masami Hiramatsu <mhiramat@kernel.org> - 2016-06-14 03:30 +0200
      Re: [PATCH tip/master] [BUGFIX] kprobes/x86: Fix to clear TF bit in  fault-on-single-stepping Ingo Molnar <mingo@kernel.org> - 2016-06-14 12:00 +0200
  [tip:perf/urgent] kprobes/x86: Clear TF bit in fault on  single-stepping tip-bot for Masami Hiramatsu <tipbot@zytor.com> - 2016-06-14 13:40 +0200

csiph-web