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From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
	Oleg Nesterov <oleg@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	"David S . Miller" <davem@davemloft.net>, X86 ML <x86@kernel.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC PATCH 1/1] x86/kprobes: Use int3 instead of debug trap for single-step
Date: Tue, 2 Mar 2021 09:41:31 +0100	[thread overview]
Message-ID: <YD36O5wCpSElA9Fi@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <161460769556.430263.12936080446789384938.stgit@devnote2>

On Mon, Mar 01, 2021 at 11:08:15PM +0900, Masami Hiramatsu wrote:
> Use int3 instead of debug trap exception for single-stepping the
> probed instructions. Some instructions which change the ip
> registers or modify IF flags are emulated because those are not
> able to be single-stepped by int3 or may allow the interrupt
> while single-stepping.
> 
> This actually changes the kprobes behavior.
> 
> - kprobes can not probe following instructions; int3, iret,
>   far jmp/call which get absolute address as immediate,
>   indirect far jmp/call, indirect near jmp/call with addressing
>   by memory (register-based indirect jmp/call are OK), and
>   vmcall/vmlaunch/vmresume/vmxoff.
> 
> - If the kprobe post_handler doesn't set before registering,
>   it may not be called in some case even if you set it afterwards.
>   (IOW, kprobe booster is enabled at registration, user can not
>    change it)
> 
> But both are rare issue, unsupported instructions will not be
> used in the kernel (or rarely used), and post_handlers are
> rarely used (I don't see it except for the test code).
> 
> Suggested-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>

Very nice!

Aside of a few nits:

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

  parent reply	other threads:[~2021-03-02  9:21 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-23 23:24 Why do kprobes and uprobes singlestep? Andy Lutomirski
2021-02-24  1:17 ` Masami Hiramatsu
2021-02-24 19:45   ` Andy Lutomirski
2021-02-25  2:22     ` Masami Hiramatsu
2021-02-25  6:03       ` Andy Lutomirski
2021-02-25  9:11         ` Masami Hiramatsu
2021-03-01 14:08       ` [RFC PATCH 0/1] x86/kprobes: Remoev single-step trap from x86 kprobes Masami Hiramatsu
2021-03-01 14:08         ` [RFC PATCH 1/1] x86/kprobes: Use int3 instead of debug trap for single-step Masami Hiramatsu
2021-03-02  8:06           ` Peter Zijlstra
2021-03-02  8:38           ` Peter Zijlstra
2021-03-02  8:41           ` Peter Zijlstra [this message]
2021-03-02  8:54             ` Peter Zijlstra
2021-03-02 12:51               ` Masami Hiramatsu
2021-03-02 13:58               ` Peter Zijlstra
2021-03-02 15:25       ` [PATCH -tip 0/3] x86/kprobes: Remoev single-step trap from x86 kprobes Masami Hiramatsu
2021-03-02 15:25         ` [PATCH -tip 1/3] x86/kprobes: Retrieve correct opcode for group instruction Masami Hiramatsu
2021-03-23 15:15           ` [tip: x86/core] " tip-bot2 for Masami Hiramatsu
2021-03-02 15:25         ` [PATCH -tip 2/3] x86/kprobes: Identify far indirect JMP correctly Masami Hiramatsu
2021-03-23 15:15           ` [tip: x86/core] " tip-bot2 for Masami Hiramatsu
2021-03-02 15:25         ` [PATCH -tip 3/3] x86/kprobes: Use int3 instead of debug trap for single-step Masami Hiramatsu
2021-03-23 15:15           ` [tip: x86/core] " tip-bot2 for Masami Hiramatsu
2021-03-17 14:55         ` [PATCH -tip 0/3] x86/kprobes: Remoev single-step trap from x86 kprobes Masami Hiramatsu
2021-03-17 16:26           ` Peter Zijlstra
2021-03-17 17:45             ` Andy Lutomirski
2021-02-25  9:59     ` Why do kprobes and uprobes singlestep? Peter Zijlstra
2021-03-01 16:51 ` Oleg Nesterov
2021-03-02  1:36   ` Andy Lutomirski
2021-03-02 20:24     ` Alexei Starovoitov
2021-03-02 21:02       ` Andy Lutomirski
2021-03-03  1:22         ` Alexei Starovoitov
2021-03-03  1:46           ` Andy Lutomirski
2021-03-03  2:18             ` Alexei Starovoitov
2021-03-03 13:27               ` Oleg Nesterov
2021-03-03 18:11               ` Daniel Xu
2021-03-03 19:14                 ` Andy Lutomirski
2021-03-02 20:25     ` Oleg Nesterov
2021-03-02 20:35       ` Andy Lutomirski
2021-03-02 20:28     ` Oleg Nesterov
2021-03-02  2:22   ` Masami Hiramatsu
2021-03-02  2:48     ` Andy Lutomirski
2021-03-02 20:31     ` Oleg Nesterov

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