linux-kernel - Re: [RFC PATCH -tip 3/3] x86/kprobes,orc: Unwind optprobe trampoline correctly

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Message-Id: <20210401105422.bc7953889a2e0aaf03201b92@kernel.org>
Date:   Thu, 1 Apr 2021 10:54:22 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        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,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH -tip 3/3] x86/kprobes,orc: Unwind optprobe
 trampoline correctly

On Wed, 31 Mar 2021 14:44:56 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:


> +#ifdef CONFIG_UNWINDER_ORC
> +unsigned long recover_optprobe_trampoline(unsigned long addr, unsigned long *sp)
> +{
> +	unsigned long offset, entry, probe_addr;
> +	struct optimized_kprobe *op;
> +	struct orc_entry *orc;
> +
> +	entry = find_kprobe_optinsn_slot_entry(addr);
> +	if (!entry)
> +		return addr;
> +
> +	offset = addr - entry;
> +
> +	/* Decode arg1 and get the optprobe */
> +	op = (void *)extract_set_arg1((void *)(entry + TMPL_MOVE_IDX));
> +	if (!op)
> +		return addr;
> +
> +	probe_addr = (unsigned long)op->kp.addr;
> +
> +	if (offset < TMPL_END_IDX) {

Maybe I should add a comment here.

/*
 * Since this is on the trampoline code based on the template code,
 * ORC information on the template code can be used for adjusting
 * stack pointer. The template code may change the stack pointer to
 * store pt_regs.
 */

> +		orc = orc_find((unsigned long)optprobe_template_func + offset);
> +		if (!orc || orc->sp_reg != ORC_REG_SP)
> +			return addr;
> +		/*
> +		 * Since optprobe trampoline doesn't push caller on the stack,
> +		 * need to decrement 1 stack entry size
> +		 */
> +		*sp += orc->sp_offset - sizeof(long);
> +		return probe_addr;
> +	} else {

/*
 * In this case, the address is on the instruction copied from probed
 * address, and jump instruction. Here the stack pointer is exactly
 * the same as the value where it was copied by the kprobes.
 */

> +		return probe_addr + offset - TMPL_END_IDX;
> +	}
> +}
> +#endif
> +


Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>