linux-kernel - Re: [PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64

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Date:   Fri, 26 Nov 2021 18:31:06 +0800
From:   "liuqi (BA)" <liuqi115@...wei.com>
To:     Mark Rutland <mark.rutland@....com>, <mhiramat@...nel.org>
CC:     <catalin.marinas@....com>, <will@...nel.org>,
        <naveen.n.rao@...ux.ibm.com>, <anil.s.keshavamurthy@...el.com>,
        <davem@...emloft.net>, <mhiramat@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <song.bao.hua@...ilicon.com>, <prime.zeng@...ilicon.com>,
        <robin.murphy@....com>, <f.fangjian@...wei.com>,
        <linuxarm@...wei.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] arm64: kprobe: Enable OPTPROBE for arm64



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.

Using optprobe_template_entry will not have this problem, as each 
optprobe has its own trampoline space (alloced in get_opinsn_slot()).

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.
> 
>> --