linux-kernel - Re: [PATCH -tip 3/5] kprobes: treewide: Remove trampoline_address from kretprobe_trampoline

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Message-ID: <alpine.LSU.2.21.2103101258070.18547@pobox.suse.cz>
Date:   Wed, 10 Mar 2021 15:21:01 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Masami Hiramatsu <mhiramat@...nel.org>
cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, kuba@...nel.org, mingo@...hat.com,
        ast@...nel.org, tglx@...utronix.de, kernel-team@...com, yhs@...com
Subject: Re: [PATCH -tip 3/5] kprobes: treewide: Remove trampoline_address
 from kretprobe_trampoline_handler()

Hi Masami,

> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -205,15 +205,23 @@ extern void arch_prepare_kretprobe(struct kretprobe_instance *ri,
>  				   struct pt_regs *regs);
>  extern int arch_trampoline_kprobe(struct kprobe *p);
>  
> +void kretprobe_trampoline(void);
> +/*
> + * Since some architecture uses structured function pointer,
> + * use arch_deref_entry_point() to get real function address.

s/arch_deref_entry_point/dereference_function_descriptor/ ?

> + */
> +static nokprobe_inline void *kretprobe_trampoline_addr(void)
> +{
> +	return dereference_function_descriptor(kretprobe_trampoline);
> +}
> +

Would it make sense to use this in s390 and powerpc reliable unwinders?

Both

arch/s390/kernel/stacktrace.c:arch_stack_walk_reliable()
arch/powerpc/kernel/stacktrace.c:__save_stack_trace_tsk_reliable()

have

	if (state.ip == (unsigned long)kretprobe_trampoline)
		return -EINVAL;

which you wanted to hide previously if I am not mistaken.

Miroslav