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From: Masami Hiramatsu <mhiramat@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>, X86 ML <x86@kernel.org>,
	Daniel Xu <dxu@dxuuu.xyz>,
	linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
	kuba@kernel.org, mingo@redhat.com, ast@kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	kernel-team@fb.com, yhs@fb.com, linux-ia64@vger.kernel.org,
	Abhishek Sagar <sagar.abhishek@gmail.com>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>
Subject: Re: [PATCH -tip v8 08/13] arm: kprobes: Make a space for regs->ARM_pc at kretprobe_trampoline
Date: Mon, 5 Jul 2021 23:40:14 +0900	[thread overview]
Message-ID: <20210705234014.4e0a9ec6a60ef2db5ff93819@kernel.org> (raw)
In-Reply-To: <YOK9Gbcd63QkU5LB@gmail.com>

On Mon, 5 Jul 2021 10:04:41 +0200
Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Masami Hiramatsu <mhiramat@kernel.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?

Since arm's kretprobe_trampoline() saves partial pt_regs, regs->ARM_pc
is not accessible (it points the caller function's stack frame).
Therefore, this extends the stack frame for storing regs->ARM_pc.

> 
> 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.

This is actually buggy from the specification viewpoint. And if
the kretprobe handler sets the instruction pointer, it must be
ignored, but in reallty, it breaks the stack frame (this does
not happen in the ftrace/perf dynamic events, but a custom kretprobe
kernel module can do this.)

Thank you,

> 
> Thanks,
> 
> 	Ingo


-- 
Masami Hiramatsu <mhiramat@kernel.org>

  reply	other threads:[~2021-07-05 14:40 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-18  7:05 [PATCH -tip v8 00/13] kprobes: Fix stacktrace with kretprobes on x86 Masami Hiramatsu
2021-06-18  7:05 ` [PATCH -tip v8 01/13] ia64: kprobes: Fix to pass correct trampoline address to the handler Masami Hiramatsu
2021-07-05  7:46   ` Ingo Molnar
2021-07-05 10:05     ` Masami Hiramatsu
2021-06-18  7:05 ` [PATCH -tip v8 02/13] kprobes: treewide: Replace arch_deref_entry_point() with dereference_symbol_descriptor() Masami Hiramatsu
2021-07-05  7:48   ` Ingo Molnar
2021-07-05 12:03     ` Masami Hiramatsu
2021-07-07 18:28   ` Andrii Nakryiko
2021-07-08  4:08     ` Masami Hiramatsu
2021-06-18  7:05 ` [PATCH -tip v8 03/13] kprobes: treewide: Remove trampoline_address from kretprobe_trampoline_handler() Masami Hiramatsu
2021-07-05  7:03   ` Ingo Molnar
2021-07-05 10:03     ` Masami Hiramatsu
2021-07-05  7:49   ` Ingo Molnar
2021-06-18  7:05 ` [PATCH -tip v8 04/13] kprobes: Add kretprobe_find_ret_addr() for searching return address Masami Hiramatsu
2021-07-05  7:42   ` Ingo Molnar
2021-07-05 14:11     ` Masami Hiramatsu
2021-06-18  7:06 ` [PATCH -tip v8 05/13] x86/kprobes: Add UNWIND_HINT_FUNC on kretprobe_trampoline code Masami Hiramatsu
2021-07-05  8:02   ` Ingo Molnar
2021-07-09 15:31     ` Masami Hiramatsu
2021-07-10  1:41       ` Masami Hiramatsu
2021-07-10 19:01         ` Josh Poimboeuf
2021-07-10 19:24           ` [PATCH 1/2] objtool: Add frame-pointer-specific function ignore Josh Poimboeuf
2021-07-11  1:16             ` Masami Hiramatsu
2021-07-29  2:31             ` Masami Hiramatsu
2021-07-10 19:25           ` [PATCH 2/2] objtool: Ignore unwind hints for ignored functions Josh Poimboeuf
2021-07-11  2:07             ` Masami Hiramatsu
2021-06-18  7:06 ` [PATCH -tip v8 06/13] ARC: Add instruction_pointer_set() API Masami Hiramatsu
2021-06-18  7:06 ` [PATCH -tip v8 07/13] ia64: " Masami Hiramatsu
2021-06-18  7:06 ` [PATCH -tip v8 08/13] arm: kprobes: Make a space for regs->ARM_pc at kretprobe_trampoline Masami Hiramatsu
2021-07-05  8:04   ` Ingo Molnar
2021-07-05 14:40     ` Masami Hiramatsu [this message]
2021-06-18  7:06 ` [PATCH -tip v8 09/13] kprobes: Enable stacktrace from pt_regs in kretprobe handler Masami Hiramatsu
2021-06-18 14:04   ` Josh Poimboeuf
2021-06-18  7:06 ` [PATCH -tip v8 10/13] x86/kprobes: Push a fake return address at kretprobe_trampoline Masami Hiramatsu
2021-07-05  8:17   ` Ingo Molnar
2021-07-09 14:55     ` Masami Hiramatsu
2021-06-18  7:07 ` [PATCH -tip v8 11/13] x86/unwind: Recover kretprobe trampoline entry Masami Hiramatsu
2021-07-05 11:36   ` Peter Zijlstra
2021-07-05 15:42     ` Masami Hiramatsu
2021-07-06  7:55       ` Peter Zijlstra
2021-07-06 15:11         ` Steven Rostedt
2021-07-07  8:20           ` Peter Zijlstra
2021-07-07  8:36             ` Peter Zijlstra
2021-07-07 10:15             ` Masami Hiramatsu
2021-07-07 10:20               ` Peter Zijlstra
2021-07-07 10:45                 ` Masami Hiramatsu
2021-07-07 13:29                   ` Masami Hiramatsu
2021-07-07 14:42                     ` Matt Wu
2021-07-11 14:09                       ` Masami Hiramatsu
2021-07-11 15:28                         ` Matt Wu
2021-07-12  4:57                           ` Masami Hiramatsu
2021-06-18  7:07 ` [PATCH -tip v8 12/13] tracing: Show kretprobe unknown indicator only for kretprobe_trampoline Masami Hiramatsu
2021-06-18  7:07 ` [PATCH -tip v8 13/13] x86/kprobes: Fixup return address in generic trampoline handler Masami Hiramatsu
2021-07-05  8:34   ` Ingo Molnar
2021-07-06 12:57     ` Masami Hiramatsu
2021-06-18 17:44 ` [PATCH -tip v8 00/13] kprobes: Fix stacktrace with kretprobes on x86 Andrii Nakryiko
2021-06-28 13:50 ` Masami Hiramatsu

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