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From:   Qi Liu <liuqi115@huawei.com>
To:     <catalin.marinas@arm.com>, <will@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
CC:     <song.bao.hua@hisilicon.com>, <prime.zeng@hisilicon.com>,
        <robin.murphy@arm.com>, <liuqi115@huawei.com>,
        <linuxarm@huawei.com>, <linux-kernel@vger.kernel.org>
Subject: [RFC PATCH] arm64: kprobes: Enable OPTPROBE for arm64
Date:   Fri, 4 Jun 2021 18:50:39 +0800
Message-ID: <1622803839-27354-1-git-send-email-liuqi115@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

This patch introduce optprobe for ARM64. In optprobe, probed
instruction is replaced by a branch instruction to detour
buffer. Detour buffer contains trampoline code and a call to
optimized_callback(). optimized_callback() calls opt_pre_handler()
to execute kprobe handler.

Limitations:
- We only support !CONFIG_RANDOMIZE_MODULE_REGION_FULL case to
guarantee the offset between probe point and kprobe pre_handler
is not larger than 128MiB.

Performance of optprobe on Hip08 platform is test using kprobe
example module[1] to analyze the latency of a kernel function,
and here is the result:

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/samples/kprobes/kretprobe_example.c

kprobe before optimized:
[280709.846380] do_empty returned 0 and took 1530 ns to execute
[280709.852057] do_empty returned 0 and took 550 ns to execute
[280709.857631] do_empty returned 0 and took 440 ns to execute
[280709.863215] do_empty returned 0 and took 380 ns to execute
[280709.868787] do_empty returned 0 and took 360 ns to execute
[280709.874362] do_empty returned 0 and took 340 ns to execute
[280709.879936] do_empty returned 0 and took 320 ns to execute
[280709.885505] do_empty returned 0 and took 300 ns to execute
[280709.891075] do_empty returned 0 and took 280 ns to execute
[280709.896646] do_empty returned 0 and took 290 ns to execute
[280709.902220] do_empty returned 0 and took 290 ns to execute
[280709.907807] do_empty returned 0 and took 290 ns to execute

optprobe:
[ 2965.964572] do_empty returned 0 and took 90 ns to execute
[ 2965.969952] do_empty returned 0 and took 80 ns to execute
[ 2965.975332] do_empty returned 0 and took 70 ns to execute
[ 2965.980714] do_empty returned 0 and took 60 ns to execute
[ 2965.986128] do_empty returned 0 and took 80 ns to execute
[ 2965.991507] do_empty returned 0 and took 70 ns to execute
[ 2965.996884] do_empty returned 0 and took 70 ns to execute
[ 2966.002262] do_empty returned 0 and took 80 ns to execute
[ 2966.007642] do_empty returned 0 and took 70 ns to execute
[ 2966.013020] do_empty returned 0 and took 70 ns to execute
[ 2966.018400] do_empty returned 0 and took 70 ns to execute
[ 2966.023779] do_empty returned 0 and took 70 ns to execute
[ 2966.029158] do_empty returned 0 and took 70 ns to execute

Signed-off-by: Qi Liu <liuqi115@huawei.com>
---
TODO:
- Veneer will be used latter to extend the range of branch and
support long jump.

 arch/arm64/Kconfig                             |   1 +
 arch/arm64/include/asm/kprobes.h               |  23 +++
 arch/arm64/kernel/probes/Makefile              |   2 +
 arch/arm64/kernel/probes/kprobes.c             |  19 ++-
 arch/arm64/kernel/probes/opt-arm64.c           | 218 +++++++++++++++++++++++++
 arch/arm64/kernel/probes/optprobe_trampoline.S |  81 +++++++++
 6 files changed, 341 insertions(+), 3 deletions(-)
 create mode 100644 arch/arm64/kernel/probes/opt-arm64.c
 create mode 100644 arch/arm64/kernel/probes/optprobe_trampoline.S

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 2e242dbb..ab1a795 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -189,6 +189,7 @@ config ARM64
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_KPROBES
+	select HAVE_OPTPROBES if !RANDOMIZE_MODULE_REGION_FULL
 	select HAVE_KRETPROBES
 	select HAVE_GENERIC_VDSO
 	select IOMMU_DMA if IOMMU_SUPPORT
diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
index 5d38ff4..9e1c492 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -39,6 +39,29 @@ void arch_remove_kprobe(struct kprobe *);
 int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
 int kprobe_exceptions_notify(struct notifier_block *self,
 			     unsigned long val, void *data);
+
+#define RELATIVEJUMP_SIZE (4)
+#define MAX_COPIED_INSN	DIV_ROUND_UP(RELATIVEJUMP_SIZE, sizeof(kprobe_opcode_t))
+struct arch_optimized_insn {
+	kprobe_opcode_t copied_insn[MAX_COPIED_INSN];
+	/* detour code buffer */
+	kprobe_opcode_t *insn;
+};
+
+/* optinsn template addresses */
+extern __visible kprobe_opcode_t optprobe_template_entry[];
+extern __visible kprobe_opcode_t optprobe_template_val[];
+extern __visible kprobe_opcode_t optprobe_template_call[];
+extern __visible kprobe_opcode_t optprobe_template_end[];
+extern __visible kprobe_opcode_t optprobe_template_restore_begin[];
+extern __visible kprobe_opcode_t optprobe_template_restore_orig_insn[];
+extern __visible kprobe_opcode_t optprobe_template_restore_end[];
+
+#define MAX_OPTIMIZED_LENGTH	4
+#define MAX_OPTINSN_SIZE				\
+	((unsigned long)optprobe_template_end -	\
+	 (unsigned long)optprobe_template_entry)
+
 void kretprobe_trampoline(void);
 void __kprobes *trampoline_probe_handler(struct pt_regs *regs);
 
diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile
index 8e4be92..52cf5d4 100644
--- a/arch/arm64/kernel/probes/Makefile
+++ b/arch/arm64/kernel/probes/Makefile
@@ -4,3 +4,5 @@ obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o	\
 				   simulate-insn.o
 obj-$(CONFIG_UPROBES)		+= uprobes.o decode-insn.o	\
 				   simulate-insn.o
+obj-$(CONFIG_OPTPROBES)		+= opt-arm64.o			\
+				   optprobe_trampoline.o
diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 66aac28..baaceed 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -11,6 +11,7 @@
 #include <linux/kernel.h>
 #include <linux/kprobes.h>
 #include <linux/extable.h>
+#include <linux/moduleloader.h>
 #include <linux/slab.h>
 #include <linux/stop_machine.h>
 #include <linux/sched/debug.h>
@@ -111,9 +112,21 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 
 void *alloc_insn_page(void)
 {
-	return __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START, VMALLOC_END,
-			GFP_KERNEL, PAGE_KERNEL_ROX, VM_FLUSH_RESET_PERMS,
-			NUMA_NO_NODE, __builtin_return_address(0));
+	void *page;
+
+	page = module_alloc(PAGE_SIZE);
+	if (!page)
+		return NULL;
+
+	set_vm_flush_reset_perms(page);
+	/*
+	 * First make the page read-only, and only then make it executable to
+	 * prevent it from being W+X in between.
+	 */
+	set_memory_ro((unsigned long)page, 1);
+	set_memory_x((unsigned long)page, 1);
+
+	return page;
 }
 
 /* arm kprobe: install breakpoint in text */
diff --git a/arch/arm64/kernel/probes/opt-arm64.c b/arch/arm64/kernel/probes/opt-arm64.c
new file mode 100644
index 0000000..09ffa75
--- /dev/null
+++ b/arch/arm64/kernel/probes/opt-arm64.c
@@ -0,0 +1,218 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Code for Kernel probes Jump optimization.
+ *
+ * Copyright (C) 2021 Hisilicon Limited
+ */
+
+#include <linux/jump_label.h>
+#include <linux/kprobes.h>
+
+#include <asm/cacheflush.h>
+#include <asm/kprobes.h>
+/* for aarch64_insn_gen_branch_imm */
+#include <asm/insn.h>
+
+#define TMPL_VAL_IDX \
+	(optprobe_template_val - optprobe_template_entry)
+#define TMPL_CALL_BACK \
+	(optprobe_template_call - optprobe_template_entry)
+#define TMPL_END_IDX \
+	(optprobe_template_end - optprobe_template_entry)
+#define TMPL_RESTORE_ORIGN_INSN \
+	(optprobe_template_restore_orig_insn - optprobe_template_entry)
+#define TMPL_RESTORE_END \
+	(optprobe_template_restore_end - optprobe_template_entry)
+
+int arch_check_optimized_kprobe(struct optimized_kprobe *op)
+{
+	return 0;
+}
+
+int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
+{
+	return optinsn->insn != NULL;
+}
+
+int arch_within_optimized_kprobe(struct optimized_kprobe *op,
+				unsigned long addr)
+{
+	return ((unsigned long)op->kp.addr <= addr &&
+		(unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
+}
+
+static void
+optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
+{
+	/* This is possible if op is under delayed unoptimizing */
+	if (kprobe_disabled(&op->kp))
+		return;
+
+	preempt_disable();
+
+	if (kprobe_running()) {
+		kprobes_inc_nmissed_count(&op->kp);
+	} else {
+		__this_cpu_write(current_kprobe, &op->kp);
+		regs->pc = (unsigned long)op->kp.addr;
+		get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+		opt_pre_handler(&op->kp, regs);
+		__this_cpu_write(current_kprobe, NULL);
+	}
+
+	preempt_enable_no_resched();
+}
+NOKPROBE_SYMBOL(optimized_callback)
+
+bool is_offset_in_branch_range(long offset)
+{
+	return (offset >= -0x08000000 && offset <= 0x07fffffc && !(offset & 0x3));
+}
+
+int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
+{
+	kprobe_opcode_t *code;
+	long rel_chk;
+	u32 insn, size;
+	int ret, i;
+	void *addr;
+
+	code = get_optinsn_slot();
+	if (!code)
+		return -ENOMEM;
+
+	/*
+	 * Verify if the address gap is in 128MiB range, because this uses
+	 * a relative jump.
+	 *
+	 * kprobe opt use a 'b' instruction to branch to optinsn.insn.
+	 * According to ARM manual, branch instruction is:
+	 *
+	 *   31  30                  25              0
+	 *  +----+---+---+---+---+---+---------------+
+	 *  |cond| 0 | 0 | 1 | 0 | 1 |     imm26     |
+	 *  +----+---+---+---+---+---+---------------+
+	 *
+	 * imm26 is a signed 26 bits integer. The real branch offset is computed
+	 * by: imm64 = SignExtend(imm26:'00', 64);
+	 *
+	 * So the maximum forward branch should be:
+	 *   (0x01ffffff << 2) = 1720x07fffffc =  0x07fffffc
+	 * The maximum backward branch should be:
+	 *   (0xfe000000 << 2) = 0xFFFFFFFFF8000000 = -0x08000000
+	 *
+	 * We can simply check (rel & 0xf8000003):
+	 *  if rel is positive, (rel & 0xf8000003) should be 0
+	 *  if rel is negitive, (rel & 0xf8000003) should be 0xf8000000
+	 *  the last '3' is used for alignment checking.
+	 */
+	rel_chk = (unsigned long)code -
+			(unsigned long)orig->addr + 8;
+	if (!is_offset_in_branch_range(rel_chk)) {
+		pr_err("%s is out of branch range.\n", orig->symbol_name);
+		free_optinsn_slot(code, 0);
+		return -ERANGE;
+	}
+
+	/* Setup template */
+	size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);
+	for (i = 0; i < size; i++) {
+		addr = code + i;
+		insn = *(optprobe_template_entry + i);
+		ret = aarch64_insn_patch_text(&addr, &insn, 1);
+		if (ret < 0) {
+			free_optinsn_slot(code, 0);
+			return -ERANGE;
+		}
+	}
+
+	/* Set probe information */
+	addr = code + TMPL_VAL_IDX;
+	insn =  (unsigned long long)op & 0xffffffff;
+	aarch64_insn_patch_text(&addr, &insn, 1);
+
+	addr = addr + 4;
+	insn = ((unsigned long long)op & GENMASK_ULL(63, 32)) >> 32;
+	aarch64_insn_patch_text(&addr, &insn, 1);
+
+	addr = code + TMPL_CALL_BACK;
+	insn =  aarch64_insn_gen_branch_imm((unsigned long)addr,
+				(unsigned long)optimized_callback,
+				AARCH64_INSN_BRANCH_LINK);
+	aarch64_insn_patch_text(&addr, &insn, 1);
+
+	/* The original probed instruction */
+	addr = code + TMPL_RESTORE_ORIGN_INSN;
+	insn =  orig->opcode;
+	aarch64_insn_patch_text(&addr, &insn, 1);
+
+	/* Jump back to next instruction */
+	addr = code + TMPL_RESTORE_END;
+	insn = aarch64_insn_gen_branch_imm(
+				(unsigned long)(&code[TMPL_RESTORE_END]),
+				(unsigned long)(op->kp.addr) + 4,
+				AARCH64_INSN_BRANCH_NOLINK);
+	aarch64_insn_patch_text(&addr, &insn, 1);
+
+	flush_icache_range((unsigned long)code,
+			   (unsigned long)(&code[TMPL_END_IDX]));
+	/* Set op->optinsn.insn means prepared. */
+	op->optinsn.insn = code;
+	return 0;
+}
+
+void arch_optimize_kprobes(struct list_head *oplist)
+{
+	struct optimized_kprobe *op, *tmp;
+
+	list_for_each_entry_safe(op, tmp, oplist, list) {
+		u32 insn;
+
+		WARN_ON(kprobe_disabled(&op->kp));
+
+		/*
+		 * Backup instructions which will be replaced
+		 * by jump address
+		 */
+		memcpy(op->optinsn.copied_insn, op->kp.addr,
+			RELATIVEJUMP_SIZE);
+		insn = aarch64_insn_gen_branch_imm((unsigned long)op->kp.addr,
+				(unsigned long)op->optinsn.insn,
+				AARCH64_INSN_BRANCH_NOLINK);
+
+		WARN_ON(insn == 0);
+
+		aarch64_insn_patch_text((void *)&(op->kp.addr), &insn, 1);
+
+		list_del_init(&op->list);
+	}
+}
+
+void arch_unoptimize_kprobe(struct optimized_kprobe *op)
+{
+	arch_arm_kprobe(&op->kp);
+}
+
+/*
+ * Recover original instructions and breakpoints from relative jumps.
+ * Caller must call with locking kprobe_mutex.
+ */
+void arch_unoptimize_kprobes(struct list_head *oplist,
+			    struct list_head *done_list)
+{
+	struct optimized_kprobe *op, *tmp;
+
+	list_for_each_entry_safe(op, tmp, oplist, list) {
+		arch_unoptimize_kprobe(op);
+		list_move(&op->list, done_list);
+	}
+}
+
+void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
+{
+	if (op->optinsn.insn) {
+		free_optinsn_slot(op->optinsn.insn, 1);
+		op->optinsn.insn = NULL;
+	}
+}
+
diff --git a/arch/arm64/kernel/probes/optprobe_trampoline.S b/arch/arm64/kernel/probes/optprobe_trampoline.S
new file mode 100644
index 0000000..95d1529
--- /dev/null
+++ b/arch/arm64/kernel/probes/optprobe_trampoline.S
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * trampoline entry and return code for optprobes.
+ */
+
+#include <linux/linkage.h>
+#include <asm/asm-offsets.h>
+#include <asm/assembler.h>
+
+	.global optprobe_template_entry
+optprobe_template_entry:
+	sub sp, sp, #PT_REGS_SIZE
+	stp x0, x1, [sp, #S_X0]
+	stp x2, x3, [sp, #S_X2]
+	stp x4, x5, [sp, #S_X4]
+	stp x6, x7, [sp, #S_X6]
+	stp x8, x9, [sp, #S_X8]
+	stp x10, x11, [sp, #S_X10]
+	stp x12, x13, [sp, #S_X12]
+	stp x14, x15, [sp, #S_X14]
+	stp x16, x17, [sp, #S_X16]
+	stp x18, x19, [sp, #S_X18]
+	stp x20, x21, [sp, #S_X20]
+	stp x22, x23, [sp, #S_X22]
+	stp x24, x25, [sp, #S_X24]
+	stp x26, x27, [sp, #S_X26]
+	stp x28, x29, [sp, #S_X28]
+	add x0, sp, #PT_REGS_SIZE
+	stp lr, x0, [sp, #S_LR]
+	/*
+	 * Construct a useful saved PSTATE
+	 */
+	mrs x0, nzcv
+	mrs x1, daif
+	orr x0, x0, x1
+	mrs x1, CurrentEL
+	orr x0, x0, x1
+	mrs x1, SPSel
+	orr x0, x0, x1
+	stp xzr, x0, [sp, #S_PC]
+	/* Get parameters to optimized_callback() */
+	ldr	x0, 1f
+	mov	x1, sp
+	/* Branch to optimized_callback() */
+	.global optprobe_template_call
+optprobe_template_call:
+	nop
+        /* Restore registers */
+	ldr x0, [sp, #S_PSTATE]
+	and x0, x0, #(PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT)
+	msr nzcv, x0
+	ldp x0, x1, [sp, #S_X0]
+	ldp x2, x3, [sp, #S_X2]
+	ldp x4, x5, [sp, #S_X4]
+	ldp x6, x7, [sp, #S_X6]
+	ldp x8, x9, [sp, #S_X8]
+	ldp x10, x11, [sp, #S_X10]
+	ldp x12, x13, [sp, #S_X12]
+	ldp x14, x15, [sp, #S_X14]
+	ldp x16, x17, [sp, #S_X16]
+	ldp x18, x19, [sp, #S_X18]
+	ldp x20, x21, [sp, #S_X20]
+	ldp x22, x23, [sp, #S_X22]
+	ldp x24, x25, [sp, #S_X24]
+	ldp x26, x27, [sp, #S_X26]
+	ldp x28, x29, [sp, #S_X28]
+	ldr lr, [sp, #S_LR]
+        add sp, sp, #PT_REGS_SIZE
+	.global optprobe_template_restore_orig_insn
+optprobe_template_restore_orig_insn:
+	nop
+	.global optprobe_template_restore_end
+optprobe_template_restore_end:
+	nop
+	.global optprobe_template_end
+optprobe_template_end:
+	.global optprobe_template_val
+optprobe_template_val:
+	1:	.long 0
+		.long 0
+
-- 
2.7.4