Messages in this thread | | | Date | Mon, 29 Nov 2021 23:35:14 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64 |
| |
Hi,
On Mon, 29 Nov 2021 14:50:22 +0800 "liuqi (BA)" <liuqi115@huawei.com> wrote:
> > > On 2021/11/29 13:00, Masami Hiramatsu wrote: > > On Mon, 29 Nov 2021 09:40:30 +0800 > > "liuqi (BA)" <liuqi115@huawei.com> wrote: > > > >> > >> > >> On 2021/11/27 20:23, Masami Hiramatsu wrote: > >>> On Fri, 26 Nov 2021 18:31:06 +0800 > >>> "liuqi (BA)" <liuqi115@huawei.com> wrote: > >>> > >>>> > >>>> > >>>> On 2021/8/24 18:50, Mark Rutland wrote: > >>>>>> diff --git a/arch/arm64/kernel/probes/optprobe_trampoline.S b/arch/arm64/kernel/probes/optprobe_trampoline.S > >>>>>> new file mode 100644 > >>>>>> index 000000000000..24d713d400cd > >>>>>> --- /dev/null > >>>>>> +++ b/arch/arm64/kernel/probes/optprobe_trampoline.S > >>>>>> @@ -0,0 +1,37 @@ > >>>>>> +/* SPDX-License-Identifier: GPL-2.0 */ > >>>>>> +/* > >>>>>> + * trampoline entry and return code for optprobes. > >>>>>> + */ > >>>>>> + > >>>>>> +#include <linux/linkage.h> > >>>>>> +#include <asm/asm-offsets.h> > >>>>>> +#include <asm/assembler.h> > >>>>>> + > >>>>>> + .global optprobe_template_entry > >>>>>> +optprobe_template_entry: > >>>>> Please use SYM_*(); see arch/arm64/kernel/entry-ftrace.S for examples of > >>>>> how to use that for trampolines. > >>>>> > >>>>> This should be: > >>>>> > >>>>> SYM_CODE_START(optprobe_template) > >>>>> > >>>> 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,
> > > > Also, the trampoline can be minimized, since what we need is the > > probed address (and the address of struct optprobe). > > A single trampoline entry will do the following; > > > > 1. push lr and a victim register (here, x0) > > 2. load the address of optprobe to x0 > > 3. call(br) common-optprobe asm code > > 4. pop lr and x0 > > 5. jump back to (next to) the original place > > > > Here the common-optprobe asm code does; > > > > c1. push all registers on the stack (like save_all_base_regs) for making > > struct pt_regs. > > c2. set the pt_regs address to x1. > > c3. call optimized_callback() > > c4. return > > > > Since arm64 will emulate the probed instruction, we can do this. > > (On the other hand, x86 needs to run the probed insn in trampoline > > code, it will do that between step 4 and 5) > > > > I'll try to minimize the trampoline according to this, > > Thanks, > Qi > > The trampoline entry code is just 5 instructions (but may need an > > immediate value (&optprobe) needs to be embedded). > > > > Thank you, > > > >> > >> Thanks, > >> Qi > >> > >>>> > >>>> So how to reuse SYM_CODE_START in this situation, does anyone has a > >>>> good idea? > >>>> > >>>> Thanks, > >>>> Qi > >>>>> ... and note the matching end below. > >>>>> > >>>>>> + sub sp, sp, #PT_REGS_SIZE > >>>>>> + save_all_base_regs > >>>>>> + /* Get parameters to optimized_callback() */ > >>>>>> + ldr x0, 1f > >>>>>> + mov x1, sp > >>>>>> + /* Branch to optimized_callback() */ > >>>>>> + .global optprobe_template_call > >>>>>> +optprobe_template_call: > >>>>> SYM_INNER_LABEL(optprobe_template_call, SYM_L_GLOBAL) > >>>>> > >>>>> ...and likewise for all the other labels. > >>>>> > >>>>>> + nop > >>>>>> + restore_all_base_regs > >>>>>> + ldr lr, [sp, #S_LR] > >>>>>> + add sp, sp, #PT_REGS_SIZE > >>>>>> + .global optprobe_template_restore_orig_insn > >>>>>> +optprobe_template_restore_orig_insn: > >>>>>> + nop > >>>>>> + .global optprobe_template_restore_end > >>>>>> +optprobe_template_restore_end: > >>>>>> + nop > >>>>>> + .global optprobe_template_end > >>>>>> +optprobe_template_end: > >>>>>> + .global optprobe_template_val > >>>>>> +optprobe_template_val: > >>>>>> + 1: .long 0 > >>>>>> + .long 0 > >>>>>> + .global optprobe_template_max_length > >>>>>> +optprobe_template_max_length: > >>>>> SYM_INNER_LABEL(optprobe_template_end, SYM_L_GLOBAL) > >>>>> SYM_CODE_END(optprobe_template) > >>>>> > >>>>> Thanks, > >>>>> Mark. > >>>>> > >>>>>> -- > >>> > >>> > > > >
-- Masami Hiramatsu <mhiramat@kernel.org>
| |