Re: [PATCH v4 04/23] arm64: kprobes: Use generic kretprobe trampoline handler

peterz
2020-08-28T13:41:46Z

On Fri, Aug 28, 2020 at 02:31:31PM +0100, Mark Rutland wrote:
> Hi,
>
> On Fri, Aug 28, 2020 at 09:27:22PM +0900, Masami Hiramatsu wrote:
> > Use the generic kretprobe trampoline handler, and use the
> > kernel_stack_pointer(regs) for framepointer verification.
> >
> > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> > ---
> > arch/arm64/kernel/probes/kprobes.c | 78 +-----------------------------------
> > 1 file changed, 3 insertions(+), 75 deletions(-)
>
> > + return (void *)kretprobe_trampoline_handler(regs, &kretprobe_trampoline,
> > + (void *)kernel_stack_pointer(regs));
> > }
> >
> > void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
> > struct pt_regs *regs)
> > {
> > ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
> > + ri->fp = (void *)kernel_stack_pointer(regs);
>
> This is probably a nomenclature problem, but what exactly is
> kretprobe_instance::fp used for?
>
> I ask because arm64's frame pointer lives in x29 (and is not necessarily
> the same as the stack pointer at function boundaries), so the naming
> is potentially misleading and possibly worth a comment or rename.

IIUC ri->rp is used for matching up the frame between the moment we
install the return trampoline on the stack and actually hitting that
trampoline.