linux-kernel - Re: [PATCH 2/4] LoongArch: Add kretprobe support

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Date:   Wed, 21 Sep 2022 16:22:39 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] LoongArch: Add kretprobe support

On 09/20/2022 11:37 AM, Tiezhu Yang wrote:

> Use the generic kretprobe trampoline handler to add kretprobe
> support for LoongArch.
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>   arch/loongarch/Kconfig          |  1 +
>   arch/loongarch/kernel/kprobes.c | 49 ++++++++++++++++++++++++++++++++++++++++-
>   2 files changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 6b01073..5f8503a 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -95,6 +95,7 @@ config LOONGARCH
>   	select HAVE_IRQ_EXIT_ON_IRQ_STACK
>   	select HAVE_IRQ_TIME_ACCOUNTING
>   	select HAVE_KPROBES
> +	select HAVE_KRETPROBES
>   	select HAVE_MOD_ARCH_SPECIFIC
>   	select HAVE_NMI
>   	select HAVE_PCI
> diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/kprobes.c
> index b2c73a5..8c3efe5 100644
> --- a/arch/loongarch/kernel/kprobes.c
> +++ b/arch/loongarch/kernel/kprobes.c
> @@ -303,7 +303,54 @@ int kprobe_exceptions_notify(struct notifier_block *self,
>   }
>   NOKPROBE_SYMBOL(kprobe_exceptions_notify);
>   
> +/*
> + * For function-return probes, init_kprobes() establishes a probepoint
> + * here. When a retprobed function returns, this probe is hit and
> + * trampoline_probe_handler() runs, calling the kretprobe's handler.
> + */
> +static void __used kretprobe_trampoline_holder(void)
> +{
> +	asm volatile(".global __kretprobe_trampoline\n"
> +		     "__kretprobe_trampoline:\n"
> +		     "nop\n");
> +}
> +
> +/* Called when the probe at kretprobe trampoline is hit */
> +static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs)
> +{
> +	instruction_pointer(regs) = __kretprobe_trampoline_handler(regs, NULL);
> +	/*
> +	 * By returning a non-zero value, we are telling
> +	 * kprobe_handler() that we don't want the post_handler
> +	 * to run (and have re-enabled preemption)
> +	 */
> +	return 1;
> +}
> +NOKPROBE_SYMBOL(trampoline_probe_handler);
> +
> +static struct kprobe trampoline_p = {
> +	.addr = (kprobe_opcode_t *)__kretprobe_trampoline,
> +	.pre_handler = trampoline_probe_handler
> +};
> +
> +void arch_prepare_kretprobe(struct kretprobe_instance *ri,
> +			    struct pt_regs *regs)
> +{
> +	ri->ret_addr = (kprobe_opcode_t *)regs->regs[1];
> +	ri->fp = NULL;
> +
> +	/* Replace the return addr with trampoline addr */
> +	regs->regs[1] = (unsigned long)__kretprobe_trampoline;
> +}
> +NOKPROBE_SYMBOL(arch_prepare_kretprobe);
> +
> +int arch_trampoline_kprobe(struct kprobe *p)
> +{
> +	return p->addr == trampoline_p.addr;
> +}
> +NOKPROBE_SYMBOL(arch_trampoline_kprobe);
> +
>   int __init arch_init_kprobes(void)
>   {
> -	return 0;
> +	return register_kprobe(&trampoline_p);
Hi, Tiezhu,

For kretprobe, we can do things like arm64/riscv... did. It avoid
the break exception when function return.

Thanks,
Jinyang
>   }