linux-kernel - Re: [PATCH -tip v8 08/13] arm: kprobes: Make a space for regs->ARM_pc at kretprobe

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Message-ID: <YOK9Gbcd63QkU5LB@gmail.com>
Date:   Mon, 5 Jul 2021 10:04:41 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, 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, Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>, kernel-team@...com,
        yhs@...com, linux-ia64@...r.kernel.org,
        Abhishek Sagar <sagar.abhishek@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Subject: Re: [PATCH -tip v8 08/13] arm: kprobes: Make a space for
 regs->ARM_pc at kretprobe_trampoline


* Masami Hiramatsu <mhiramat@...nel.org> wrote:

> Change kretprobe_trampoline to make a space for regs->ARM_pc so that
> kretprobe_trampoline_handler can call instruction_pointer_set()
> safely.

The idiom is "make space", but in any case, what does this mean?

Was the stack frame set up in kretprobe_trampoline() and calling 
trampoline_handler() buggy?

If yes, then explain the bad effects of the bug, and make all of this clear 
in the title & changelog.

Thanks,

	Ingo