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>
next prev parent reply other threads:[~2022-05-11 14:35 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220511233450.40136cdf6a53eb32cd825be8@kernel.org \
--to=mhiramat@kernel.org \
--cc=bobo.shaobowang@huawei.com \
--cc=catalin.marinas@arm.com \
--cc=cj.chengjian@huawei.com \
--cc=huawei.libin@huawei.com \
--cc=jolsa@kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=liwei391@huawei.com \
--cc=mark.rutland@arm.com \
--cc=rostedt@goodmis.org \
--cc=will@kernel.org \
--cc=xiexiuqi@huawei.com \
--cc=zengshun.wu@outlook.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).