From: Masami Hiramatsu <firstname.lastname@example.org>
To: "liuqi (BA)" <email@example.com>
Cc: Linuxarm <firstname.lastname@example.org>,
Mark Rutland <email@example.com>, <firstname.lastname@example.org>,
Subject: Re: [PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64
Date: Wed, 1 Dec 2021 10:50:01 +0900 [thread overview]
Message-ID: <email@example.com> (raw)
On Tue, 30 Nov 2021 14:48:06 +0800
"liuqi (BA)" <firstname.lastname@example.org> wrote:
> On 2021/11/29 22:35, Masami Hiramatsu wrote:
> >>>>>> Hi all,
> >>>>>> I meet a problem when I use SYM_CODE_START(optprobe_template) to replace
> >>>>>> optprobe_template_entry.
> >>>>>> If SYM_CODE_START is used, all optprobe will share one trampoline space.
> >>>>>> Under this circumstances, if user register two optprobes, trampoline
> >>>>>> will be overwritten by the newer one, and this will cause kernel panic
> >>>>>> when the old optprobe is trigger.
> >>>>> Hm, this is curious, because the template should be copied to the
> >>>>> trampoline buffer for each optprobe and be modified.
> >>>>>> Using optprobe_template_entry will not have this problem, as each
> >>>>>> optprobe has its own trampoline space (alloced in get_opinsn_slot()).
> >>>>> Yes, it is designed to do so.
> >>>>> Thank you,
> >>>> Hi Masami,
> >>>> Thanks for your reply. But I also met a problem when using
> >>>> get_opinsn_slot() to alloc trampoline buffer.
> >>>> As module_alloc(like x86) is used to alloc buffer, trampoline is in
> >>>> module space, so if origin insn is in kernel space, the range between
> >>>> origin insn and trampoline is out of 128M.
> >>>> As module PLT cannot used here, I have no idea to achieve long jump in
> >>>> this situation. Do you have any good idea?
> >> Hi Masami,
> >> Thanks so much for your reply.
> >>> One possible solution is to use pre-allocated trampoline space in
> >>> the text area, as same as ppc64 does.
> >>> (See arch/powerpc/kernel/optprobes_head.S, it embeds a space at "optinsn_slot")
> >> I find something interesting in arch/powerpc/kernel/optprobes.c, it use
> >> "optinsn_slot" as a public buffer, and use a static "insn_page_in_use"
> >> to make sure there is only one optprobe in kernel.
> >> If we use this solution , users could only register one optprobe each
> >> time. This will also be a limitation for users, what's your opinion
> >> about this?
> > No, that is just a memory area for pooling trampoline buffer. So optprobe
> > can allocate the buffer from that area. Please see kernel/kprobes.c:344.
> > optprobe allocates "insn_slot" from kprobe_optinsn_slots, which uses
> > alloc_optinsn_page() to allocate the pool of slots.
> > Thank you,
> Thanks for your reply, I test alloc_optinsn_page() and it does work well
> to alloc the pool of slots.
> But when I tried to use module PLT, something seems wrong here.
> Arm64 Module PLT in mod->arch.ftrace_trampolines is set in
> module_finalize, after that, mod->arch.ftrace_trampolines seems to be a
> read-only memory. But in arch_optimize_kprobes() we need to modify the
> destination of PLT (as each optprobe has its own trampoline buffer), if
> so, we cannot get rid of the 128M branch limit :(
Hmm, OK, we need to introduce trampoline buffer allocation pool for modules
for such arch. But that should be another story. I think you should start
from the core-kernel. At this moment, if the probe address is in the module,
please return -ERANGE from arch_prepare_optimized_kprobe().
Module support must be done in the next step (series), since that will involve
the kprobes generic code change.
Masami Hiramatsu <email@example.com>
next prev parent reply other threads:[~2021-12-01 1:53 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-18 7:33 [PATCH v4 0/2] arm64: Enable OPTPROBE for arm64 Qi Liu
2021-08-18 7:33 ` [PATCH v4 1/2] Make save_all_base_regs and restore_all_base_regs as common macro Qi Liu
2021-08-18 7:33 ` [PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64 Qi Liu
2021-08-18 16:27 ` Masami Hiramatsu
2021-08-24 10:50 ` Mark Rutland
2021-08-24 11:50 ` Barry Song
2021-08-24 12:11 ` Mark Rutland
2021-08-24 12:42 ` Barry Song
2021-08-25 2:13 ` Masami Hiramatsu
2021-08-25 3:12 ` Barry Song
2021-09-07 3:14 ` liuqi (BA)
2021-11-26 10:31 ` liuqi (BA)
2021-11-27 12:23 ` Masami Hiramatsu
2021-11-29 1:40 ` liuqi (BA)
2021-11-29 5:00 ` Masami Hiramatsu
2021-11-29 6:50 ` liuqi (BA)
2021-11-29 14:35 ` Masami Hiramatsu
2021-11-30 6:48 ` liuqi (BA)
2021-12-01 1:50 ` Masami Hiramatsu [this message]
2021-12-01 2:55 ` liuqi (BA)
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