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From: Masami Hiramatsu <mhiramat@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Wang ShaoBo <bobo.shaobowang@huawei.com>,
	cj.chengjian@huawei.com, huawei.libin@huawei.com,
	xiexiuqi@huawei.com, liwei391@huawei.com,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com,
	will@kernel.org, zengshun.wu@outlook.com,
	Jiri Olsa <jolsa@kernel.org>
Subject: Re: [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines
Date: Wed, 11 May 2022 23:34:50 +0900	[thread overview]
Message-ID: <20220511233450.40136cdf6a53eb32cd825be8@kernel.org> (raw)
In-Reply-To: <20220510104446.6d23b596@gandalf.local.home>

On Tue, 10 May 2022 10:44:46 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 10 May 2022 18:10:12 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > >
> > > This was suggested by both Peter Zijlstra and Thomas Gleixner when I
> > > introduced FTRACE_WITH_ARGS, where all functions can now get the arguments
> > > from fregs, but not the full pt_regs.  
> > 
> > Hmm, I thought the ftrace_get_regs() is the all-or-nothing interface, or
> > is there any way to get the arguments from fregs?
> 
> Not yet generically. But that can easily be added. If you look at x86 live
> patching, since it is arch specific, it just took the regs parameter
> directly, knowing that the args were already set up. That is, ftrace_regs is
> just a wrapper around pt_regs with just the regs for the arguments and stack
> initialized. If you get regs from ftrace_get_regs(fregs) it will return
> NULL if it wasn't full set of regs. But we can add generic functions to get
> the parameters.
> 
> That is, we can create a ftrace_get_kernel_argument() function that takes
> fregs instead of pt_regs, and produce the same thing as
> regs_get_kernel_argument().
> 
> x86 live kernel patching has this:
> 
> arch/x86/include/asm/ftrace.h:
> 
>  #define ftrace_instruction_pointer_set(fregs, _ip)     \
>        do { (fregs)->regs.ip = (_ip); } while (0)
> 
> 
> arch/x86/include/asm/livepatch.h:
> 
>  static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
>  {
>         ftrace_instruction_pointer_set(fregs, ip);
>  }
> 
> Where fregs is not a full set of regs.

OK, so fregs::regs will have a subset of pt_regs, and accessibility of
the registers depends on the architecture. If we can have a checker like

ftrace_regs_exist(fregs, reg_offset)

kprobe on ftrace or fprobe user (BPF) can filter user's requests.
I think I can introduce a flag for kprobes so that user can make a
kprobe handler only using a subset of registers. 
Maybe similar filter code is also needed for BPF 'user space' library
because this check must be done when compiling BPF.

Thank you,


> > 
> > > If a ftrace_ops has the REGS flag set
> > > (using ftrace_regs_caller), the ftrace_get_regs(fregs) will return the
> > > pt_regs, or it will return NULL if ftrace_regs_caller was not used.
> > > 
> > > This way the same parameter can provide full pt_regs or a subset, and have
> > > an generic interface to tell the difference.  
> > 
> > If it can provide a partial (subset of) pt_regs, that could be good for me
> > too, since at least kprobe-events on ftrace can check the traced register
> > is in the subset or not and reject it if it doesn't saved.
> 
> That's exactly the use case for ftrace_regs.
> 
> -- Steve


-- 
Masami Hiramatsu <mhiramat@kernel.org>

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  reply	other threads:[~2022-05-11 14:36 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-16 10:01 [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 1/4] arm64: introduce aarch64_insn_gen_load_literal Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 2/4] arm64/ftrace: introduce ftrace dynamic trampoline entrances Wang ShaoBo
2022-03-16 10:01 ` [RFC PATCH -next v2 3/4] arm64/ftrace: support dynamically allocated trampolines Wang ShaoBo
2022-04-21 13:10   ` Mark Rutland
2022-04-21 14:06     ` Steven Rostedt
2022-04-21 14:08       ` Steven Rostedt
2022-04-21 15:14       ` Mark Rutland
2022-04-21 15:42         ` Steven Rostedt
2022-04-21 16:27           ` Mark Rutland
2022-04-21 17:06             ` Steven Rostedt
2022-04-22 10:12               ` Mark Rutland
2022-04-22 15:45                 ` Steven Rostedt
2022-04-22 17:27                   ` Mark Rutland
2022-04-26  8:47                     ` Masami Hiramatsu
2022-05-04 10:24                       ` Mark Rutland
2022-05-05  3:15                         ` Masami Hiramatsu
2022-05-09 18:22                           ` Steven Rostedt
2022-05-10  9:10                             ` Masami Hiramatsu
2022-05-10 14:44                               ` Steven Rostedt
2022-05-11 14:34                                 ` Masami Hiramatsu [this message]
2022-05-11 15:12                                   ` Steven Rostedt
2022-05-12 12:02                                     ` Masami Hiramatsu
2022-05-12 13:50                                       ` Steven Rostedt
2022-05-25 12:17                                       ` Mark Rutland
2022-05-25 13:43                                         ` Steven Rostedt
2022-05-25 17:12                                           ` Mark Rutland
2022-05-30  1:03                                         ` Masami Hiramatsu
2022-05-30 12:38                                           ` Jiri Olsa
2022-05-31  1:00                                             ` Masami Hiramatsu
2022-05-04 12:43               ` Mark Rutland
2022-05-05  2:57             ` Wangshaobo (bobo)
2022-05-25 12:27               ` Mark Rutland
2022-04-27  8:54       ` Wangshaobo (bobo)
2022-03-16 10:01 ` [RFC PATCH -next v2 4/4] arm64/ftrace: implement long jump for dynamic trampolines Wang ShaoBo
2022-04-21 13:47   ` Mark Rutland
2022-03-16 14:29 ` [RFC PATCH -next v2 0/4] arm64/ftrace: support dynamic trampoline Steven Rostedt
2022-04-20 18:11 ` Steven Rostedt
2022-04-21  1:13   ` Wangshaobo (bobo)
2022-04-21 12:37     ` Steven Rostedt
2022-05-25 12:45       ` Mark Rutland
2022-05-25 13:58         ` Steven Rostedt
2022-05-25 17:26           ` Mark Rutland
2022-04-21 12:53 ` Mark Rutland

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