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Message-ID: <YlW/CdzKGeSYqtHY@FVFF77S0Q05N.cambridge.arm.com>
Date: Tue, 12 Apr 2022 19:03:53 +0100
From: Mark Rutland <mark.rutland@....com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>,
Alexei Starovoitov <alexei.starovoitov@...il.com>,
Daniel Borkmann <daniel@...earbox.net>,
Shubham Bansal <illusionist.neo@...il.com>,
Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
kernel-team@...com, Jiri Olsa <jolsa@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
"Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
"David S . Miller" <davem@...emloft.net>,
linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
Ard Biesheuvel <ardb@...nel.org>,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH bpf v2 0/4] kprobes: rethook,ARM,arm64: Replace kretprobe
trampoline with rethook
On Fri, Apr 08, 2022 at 09:50:35AM +0900, Masami Hiramatsu wrote:
> Hi,
Hi,
> Here is the 2nd version of the series for replacing kretprobe trampoline
> with rethook on ARM/arm64. I fixed some compiler warnings in this version.
What tree is this based on? It doesn't cleanly apply atop v5.18-rc1:
| [mark@...rids:~/src/linux]% git am v2_20220408_mhiramat_kprobes_rethook_arm_arm64_replace_kretprobe_trampoline_with_rethook.mbx
| Applying: ARM: unwind: Initialize the lr_addr field of unwind_ctrl_block
| Applying: rethook,fprobe,kprobes: Check a failure in the rethook_hook()
| Applying: ARM: rethook: Replace kretprobe trampoline with rethook
| error: patch failed: arch/arm/kernel/stacktrace.c:66
| error: arch/arm/kernel/stacktrace.c: patch does not apply
| Patch failed at 0003 ARM: rethook: Replace kretprobe trampoline with rethook
| hint: Use 'git am --show-current-patch=diff' to see the failed patch
| When you have resolved this problem, run "git am --continue".
| If you prefer to skip this patch, run "git am --skip" instead.
| To restore the original branch and stop patching, run "git am --abort".
I've done a `git am -3` locally to make that work for now.
> The previous version is here[1];
>
> [1] https://lore.kernel.org/all/164915121498.982637.12787715964983738566.stgit@devnote2/T/#u
>
> This series includes a trivial bugfix for the arm unwinder to initialize
> an internal data structure([1/4]). This is not critical for stack trace,
> but required for rethook to find the LR register from the stack.
> This also have an update for the rethook interface, which allows us to
> check the rethook_hook() failure ([2/4]). This is also required for the
> rethook on arm because unwinder is able to fail.
> The rest of patches are replacing kretprobe trampoline with rethook on
> ARM ([3/4]) and arm64 ([4/4]).
Generally, the arm and arm64 bits go via different trees, and for unwinding the
two are quite different.
IIUC the dependency between the two is just because patch 2 changes the
prototypes of some functions. Is that right?
> Background:
>
> This rethook came from Jiri's request of multiple kprobe for bpf[2].
> He tried to solve an issue that starting bpf with multiple kprobe will
> take a long time because bpf-kprobe will wait for RCU grace period for
> sync rcu events.
>
> Jiri wanted to attach a single bpf handler to multiple kprobes and
> he tried to introduce multiple-probe interface to kprobe. So I asked
> him to use ftrace and kretprobe-like hook if it is only for the
> function entry and exit, instead of adding ad-hoc interface
> to kprobes.
> For this purpose, I introduced the fprobe (kprobe like interface for
> ftrace) with the rethook (this is a generic return hook feature for
> fprobe exit handler)[3].
>
> [2] https://lore.kernel.org/all/20220104080943.113249-1-jolsa@kernel.org/T/#u
> [3] https://lore.kernel.org/all/164191321766.806991.7930388561276940676.stgit@devnote2/T/#u
>
> The rethook is basically same as the kretprobe trampoline. I just made
> it decoupled from kprobes. Eventually, the all arch dependent kretprobe
> trampolines will be replaced with the rethook trampoline instead of
> cloning the code.
>
> When I port the rethook for all arch which supports kretprobe, the
> legacy kretprobe specific code (which is for CONFIG_KRETPROBE_ON_RETHOOK=n)
> will be removed eventually.
>
> BTW, the arm Clang support for rethook is for kretprobes only. fprobe
> and ftrace seems not working with Clang yet.
Do you mean that's an existing issue?
Thanks,
Mark.
>
> Thank you,
>
> ---
>
> Masami Hiramatsu (4):
> ARM: unwind: Initialize the lr_addr field of unwind_ctrl_block
> rethook,fprobe,kprobes: Check a failure in the rethook_hook()
> ARM: rethook: Replace kretprobe trampoline with rethook
> arm64: rethook: Replace kretprobe trampoline with rethook
>
>
> arch/arm/Kconfig | 1
> arch/arm/include/asm/stacktrace.h | 5 +
> arch/arm/kernel/stacktrace.c | 13 +--
> arch/arm/kernel/unwind.c | 1
> arch/arm/probes/Makefile | 1
> arch/arm/probes/kprobes/core.c | 62 ------------
> arch/arm/probes/rethook.c | 127 +++++++++++++++++++++++++
> arch/arm64/Kconfig | 1
> arch/arm64/include/asm/kprobes.h | 2
> arch/arm64/include/asm/stacktrace.h | 2
> arch/arm64/kernel/Makefile | 1
> arch/arm64/kernel/probes/Makefile | 1
> arch/arm64/kernel/probes/kprobes.c | 15 ---
> arch/arm64/kernel/probes/kprobes_trampoline.S | 86 -----------------
> arch/arm64/kernel/rethook.c | 28 ++++++
> arch/arm64/kernel/rethook_trampoline.S | 87 +++++++++++++++++
> arch/arm64/kernel/stacktrace.c | 9 +-
> arch/x86/kernel/rethook.c | 4 +
> include/linux/rethook.h | 4 -
> kernel/kprobes.c | 8 +-
> kernel/trace/fprobe.c | 5 +
> kernel/trace/rethook.c | 12 ++
> 22 files changed, 287 insertions(+), 188 deletions(-)
> create mode 100644 arch/arm/probes/rethook.c
> delete mode 100644 arch/arm64/kernel/probes/kprobes_trampoline.S
> create mode 100644 arch/arm64/kernel/rethook.c
> create mode 100644 arch/arm64/kernel/rethook_trampoline.S
>
> --
> Masami Hiramatsu (Linaro) <mhiramat@...nel.org>
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