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From:   Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Will Deacon <will@kernel.org>,
        "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
CC:     Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Mark Rutland <mark.rutland@arm.com>
Subject: [PATCH v4] arm64: implement KPROBES_ON_FTRACE
Thread-Topic: [PATCH v4] arm64: implement KPROBES_ON_FTRACE
Thread-Index: AQHVWJwQA6oCa6sgREe9v4FYsERl0w==
Date:   Thu, 22 Aug 2019 03:45:38 +0000
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KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it
eliminates the need for a trap, as well as the need to emulate or
single-step instructions.

Tested on berlin arm64 platform.

~ # mount -t debugfs debugfs /sys/kernel/debug/
~ # cd /sys/kernel/debug/
/sys/kernel/debug # echo 'p _do_fork' > tracing/kprobe_events

before the patch:

/sys/kernel/debug # cat kprobes/list
ffffff801009fe28  k  _do_fork+0x0    [DISABLED]

after the patch:

/sys/kernel/debug # cat kprobes/list
ffffff801009ff54  k  _do_fork+0x4    [DISABLED][FTRACE]

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
---
KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it
eliminates the need for a trap, as well as the need to emulate or
single-step instructions.

Applied after arm64 FTRACE_WITH_REGS:
http://lists.infradead.org/pipermail/linux-arm-kernel/2019-August/674404.ht=
ml

Changes since v3:
  - move kprobe_lookup_name() and arch_kprobe_on_func_entry to ftrace.c sin=
ce
    we only want to choose the ftrace entry for KPROBES_ON_FTRACE.
  - only choose ftrace entry if (addr && !offset)

Changes since v2:
  - remove patch1, make it a single cleanup patch
  - remove "This patch" in the change log
  - implement arm64's kprobe_lookup_name() and arch_kprobe_on_func_entry in=
stead
    of patching the common kprobes code

Changes since v1:
  - make the kprobes/x86: use instruction_pointer and instruction_pointer_s=
et
    as patch1
  - add Masami's ACK to patch1
  - add some description about KPROBES_ON_FTRACE and why we need it on
    arm64
  - correct the log before the patch
  - remove the consolidation patch, make it as TODO
  - only adjust kprobe's addr when KPROBE_FLAG_FTRACE is set
  - if KPROBES_ON_FTRACE, ftrace_call_adjust() the kprobe's addr before
    calling ftrace_location()
  - update the kprobes-on-ftrace/arch-support.txt in doc


 .../debug/kprobes-on-ftrace/arch-support.txt  |  2 +-
 arch/arm64/Kconfig                            |  1 +
 arch/arm64/kernel/probes/Makefile             |  1 +
 arch/arm64/kernel/probes/ftrace.c             | 84 +++++++++++++++++++
 4 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/kernel/probes/ftrace.c

diff --git a/Documentation/features/debug/kprobes-on-ftrace/arch-support.tx=
t b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt
index 68f266944d5f..e8358a38981c 100644
--- a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt
+++ b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt
@@ -9,7 +9,7 @@
     |       alpha: | TODO |
     |         arc: | TODO |
     |         arm: | TODO |
-    |       arm64: | TODO |
+    |       arm64: |  ok  |
     |         c6x: | TODO |
     |        csky: | TODO |
     |       h8300: | TODO |
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 663392d1eae2..928700f15e23 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -167,6 +167,7 @@ config ARM64
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_KPROBES
+	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_KRETPROBES
 	select HAVE_GENERIC_VDSO
 	select IOMMU_DMA if IOMMU_SUPPORT
diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/M=
akefile
index 8e4be92e25b1..4020cfc66564 100644
--- a/arch/arm64/kernel/probes/Makefile
+++ b/arch/arm64/kernel/probes/Makefile
@@ -4,3 +4,4 @@ obj-$(CONFIG_KPROBES)		+=3D kprobes.o decode-insn.o	\
 				   simulate-insn.o
 obj-$(CONFIG_UPROBES)		+=3D uprobes.o decode-insn.o	\
 				   simulate-insn.o
+obj-$(CONFIG_KPROBES_ON_FTRACE)	+=3D ftrace.o
diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/probes/f=
trace.c
new file mode 100644
index 000000000000..5989c57660f3
--- /dev/null
+++ b/arch/arm64/kernel/probes/ftrace.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Dynamic Ftrace based Kprobes Optimization
+ *
+ * Copyright (C) Hitachi Ltd., 2012
+ * Copyright (C) 2019 Jisheng Zhang <jszhang@kernel.org>
+ *		      Synaptics Incorporated
+ */
+
+#include <linux/kprobes.h>
+
+/* Ftrace callback handler for kprobes -- called under preepmt disabed */
+void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
+			   struct ftrace_ops *ops, struct pt_regs *regs)
+{
+	struct kprobe *p;
+	struct kprobe_ctlblk *kcb;
+
+	/* Preempt is disabled by ftrace */
+	p =3D get_kprobe((kprobe_opcode_t *)ip);
+	if (unlikely(!p) || kprobe_disabled(p))
+		return;
+
+	kcb =3D get_kprobe_ctlblk();
+	if (kprobe_running()) {
+		kprobes_inc_nmissed_count(p);
+	} else {
+		unsigned long orig_ip =3D instruction_pointer(regs);
+		/* Kprobe handler expects regs->pc =3D pc + 4 as breakpoint hit */
+		instruction_pointer_set(regs, ip + sizeof(kprobe_opcode_t));
+
+		__this_cpu_write(current_kprobe, p);
+		kcb->kprobe_status =3D KPROBE_HIT_ACTIVE;
+		if (!p->pre_handler || !p->pre_handler(p, regs)) {
+			/*
+			 * Emulate singlestep (and also recover regs->pc)
+			 * as if there is a nop
+			 */
+			instruction_pointer_set(regs,
+				(unsigned long)p->addr + MCOUNT_INSN_SIZE);
+			if (unlikely(p->post_handler)) {
+				kcb->kprobe_status =3D KPROBE_HIT_SSDONE;
+				p->post_handler(p, regs, 0);
+			}
+			instruction_pointer_set(regs, orig_ip);
+		}
+		/*
+		 * If pre_handler returns !0, it changes regs->pc. We have to
+		 * skip emulating post_handler.
+		 */
+		__this_cpu_write(current_kprobe, NULL);
+	}
+}
+NOKPROBE_SYMBOL(kprobe_ftrace_handler);
+
+kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
+{
+	unsigned long addr =3D kallsyms_lookup_name(name);
+
+	if (addr && !offset) {
+		unsigned long faddr;
+		/*
+		 * with -fpatchable-function-entry=3D2, the first 4 bytes is the
+		 * LR saver, then the actual call insn. So ftrace location is
+		 * always on the first 4 bytes offset.
+		 */
+		faddr =3D ftrace_location_range(addr,
+					      addr + AARCH64_INSN_SIZE);
+		if (faddr)
+			return (kprobe_opcode_t *)faddr;
+	}
+	return (kprobe_opcode_t *)addr;
+}
+
+bool arch_kprobe_on_func_entry(unsigned long offset)
+{
+	return offset <=3D AARCH64_INSN_SIZE;
+}
+
+int arch_prepare_kprobe_ftrace(struct kprobe *p)
+{
+	p->ainsn.api.insn =3D NULL;
+	return 0;
+}
--=20
2.23.0.rc1