[PATCH v1 2/2] arm64: kprobes: add support for KPROBES_ON_FTRACE

[Janet Liu]

From: Janet Liu <janet.liu@xxxxxxxxxx>

This patch allow kprobes on ftrace call sites. This optimization
avoids use of a trap with regular kprobes.

This depends on HAVE_DYNAMIC_FTRACE_WITH_REGS which depends on
"patchable-function-entry" options which is only implemented with newer
toolchains.

Signed-off-by: Janet Liu <janet.liu@xxxxxxxxxx>
---
 arch/arm64/Kconfig                 |  1 +
 arch/arm64/kernel/probes/Makefile  |  1 +
 arch/arm64/kernel/probes/ftrace.c  | 73 ++++++++++++++++++++++++++++++++++++++
 arch/arm64/kernel/probes/kprobes.c | 27 ++++++++++++++
 4 files changed, 102 insertions(+)
 create mode 100644 arch/arm64/kernel/probes/ftrace.c

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index ab07251..c3fd0dd 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -200,6 +200,7 @@ config ARM64
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_KPROBES
 	select HAVE_OPTPROBES
+	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/Makefile
index c77c92a..d9b204f 100644
--- a/arch/arm64/kernel/probes/Makefile
+++ b/arch/arm64/kernel/probes/Makefile
@@ -3,5 +3,6 @@ obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o	\
 				   kprobes_trampoline.o		\
 				   simulate-insn.o
 obj-$(CONFIG_OPTPROBES) 	+= opt.o opt_head.o
+obj-$(CONFIG_KPROBES_ON_FTRACE) += ftrace.o
 obj-$(CONFIG_UPROBES)		+= uprobes.o decode-insn.o	\
 				   simulate-insn.o
diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/probes/ftrace.c
new file mode 100644
index 0000000..46ea92e
--- /dev/null
+++ b/arch/arm64/kernel/probes/ftrace.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-only
+//
+// Dynamic Ftrace based Kprobes Optimization
+//
+// Copyright (C) 2021, Unisoc Inc.
+// Author: Janet Liu <janet.liu@xxxxxxxxxx>
+#include <linux/kprobes.h>
+#include <linux/ptrace.h>
+#include <linux/hardirq.h>
+#include <linux/preempt.h>
+#include <linux/ftrace.h>
+
+
+/* Ftrace callback handler for kprobes*/
+void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
+			   struct ftrace_ops *ops, struct ftrace_regs *fregs)
+{
+	struct kprobe *p;
+	struct kprobe_ctlblk *kcb;
+	struct pt_regs *regs = ftrace_get_regs(fregs);
+	int bit;
+
+	bit = ftrace_test_recursion_trylock(ip, parent_ip);
+	if (bit < 0)
+		return;
+
+	preempt_disable_notrace();
+	p = get_kprobe((kprobe_opcode_t *)ip);
+	if (unlikely(!p) || kprobe_disabled(p))
+		goto end;
+
+	kcb = get_kprobe_ctlblk();
+	if (kprobe_running()) {
+		kprobes_inc_nmissed_count(p);
+	} else {
+		unsigned long orig_ip = instruction_pointer(regs);
+
+		instruction_pointer_set(regs, ip);
+
+		__this_cpu_write(current_kprobe, p);
+		kcb->kprobe_status = 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 = 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);
+	}
+end:
+	preempt_enable_notrace();
+	ftrace_test_recursion_unlock(bit);
+}
+NOKPROBE_SYMBOL(kprobe_ftrace_handler);
+
+int arch_prepare_kprobe_ftrace(struct kprobe *p)
+{
+	p->ainsn.api.insn = NULL;
+	p->ainsn.api.restore = 0;
+	return 0;
+}
diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 6dbcc89..3d371d3 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -417,6 +417,33 @@ int __kprobes arch_trampoline_kprobe(struct kprobe *p)
 	return 0;
 }
 
+kprobe_opcode_t __kprobes *kprobe_lookup_name(const char *name, unsigned int offset)
+{
+	kprobe_opcode_t *addr;
+
+	addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);
+#ifdef CONFIG_KPROBES_ON_FTRACE
+	if (addr && !offset) {
+		unsigned long faddr;
+
+		faddr = ftrace_location_range((unsigned long)addr,
+					      (unsigned long)addr + 8);
+		if (faddr)
+			addr = (kprobe_opcode_t *)faddr;
+	}
+#endif
+	return addr;
+}
+
+bool __kprobes arch_kprobe_on_func_entry(unsigned long offset)
+{
+#ifdef CONFIG_KPROBES_ON_FTRACE
+	return offset <= 8;
+#else
+	return !offset;
+#endif
+}
+
 int __init arch_init_kprobes(void)
 {
 	register_kernel_break_hook(&kprobes_break_hook);
-- 
1.9.1