Re: [PATCH -tip] x86/kprobes: Drop removed INT3 handling code

From: Google
Date: Tue Nov 29 2022 - 11:28:29 EST


On Mon, 28 Nov 2022 15:49:05 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Fri, 25 Nov 2022 23:44:47 +0900
> "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote:
>
> > From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> >
> > Drop removed INT3 handling code from kprobe_int3_handler() because this
> > case (get_kprobe() doesn't return corresponding kprobe AND the INT3 is
> > removed) must not happen with the kprobe managed INT3, but can happen
> > with the non-kprobe INT3, which should be handled by other callbacks.
> >
> > For the kprobe managed INT3, the arch_disarm_kprobe() removes the INT3
> > and then calls text_poke_sync(). Since this text_poke_sync() uses IPI
> > to call sync_core() on all online cpus, that ensures that all running
> > INT3 exception handlers have done.
> > And, the unregister_kprobe() will remove the kprobe from the hash table
> > after arch_disarm_kprobe().
> >
> > Thus, when the kprobe managed INT3 hits, kprobe_int3_handler() should
> > be able to find corresponding kprobe always by get_kprobe(). If it can
> > not find any kprobe, this means that is NOT a kprobe managed INT3.
> >
>
> I believe this was fixed by:
>
> 5c02ece81848d ("x86/kprobes: Fix ordering while text-patching")
>
> That should be mentioned in the commit log.

Thanks for pointing! Yes, it ensures since it add text_poke_sync()
in arch_arm/disarm_kprobe(). So this is the last part of the
commit 5c02ece81848d.

>
> Anyway, looks good.
>
> Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>

Thank you!

>
> -- Steve
>
>
>
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> > ---
> > arch/x86/kernel/kprobes/core.c | 14 --------------
> > 1 file changed, 14 deletions(-)
> >
> > diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> > index 66299682b6b7..33390ed4dcf3 100644
> > --- a/arch/x86/kernel/kprobes/core.c
> > +++ b/arch/x86/kernel/kprobes/core.c
> > @@ -986,20 +986,6 @@ int kprobe_int3_handler(struct pt_regs *regs)
> > kprobe_post_process(p, regs, kcb);
> > return 1;
> > }
> > - }
> > -
> > - if (*addr != INT3_INSN_OPCODE) {
> > - /*
> > - * The breakpoint instruction was removed right
> > - * after we hit it. Another cpu has removed
> > - * either a probepoint or a debugger breakpoint
> > - * at this address. In either case, no further
> > - * handling of this interrupt is appropriate.
> > - * Back up over the (now missing) int3 and run
> > - * the original instruction.
> > - */
> > - regs->ip = (unsigned long)addr;
> > - return 1;
> > } /* else: not a kprobe fault; let the kernel handle it */
> >
> > return 0;
>


--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>