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Subject[PATCH v5] arm64: kprobe: Enable OPTPROBE for arm64
Date
This patch introduce optprobe for ARM64. In optprobe, probed
instruction is replaced by a branch instruction to trampoline.

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:

common kprobe:
[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

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

As the result shows, optprobe can greatly reduce the latency. Big
latency of common kprobe will significantly impact the real result
while doing performance analysis or debugging performance issues
in lab, so optprobe is useful in this scenario.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Qi Liu <liuqi115@huawei.com>

Note:
As branch instruction in Arm64 has a 128M range limitation, optprobe
could only used when offset between probe point and trampoline
is less than 128M, otherwise kernel will choose common kprobe
automaticly.

Limitation caused by branch isn't unique to Arm64, but also to
x86/arm/powerpc.

In fact, Module PLT has been tried to get rid of limiation, but
destination of PLT must be a fixed value, and we need to modify
the destination (as each optprobe has its own trampoline).

As discussed with Masami[2], we can start with core-kernel point
(within 128M) as the first step, like other architectures.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/samples/kprobes/kretprobe_example.c
[2] https://lore.kernel.org/lkml/20211201105001.5164f98ba783e7207df1229c@kernel.org/
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/kprobes.h | 21 ++
arch/arm64/kernel/probes/Makefile | 2 +
arch/arm64/kernel/probes/opt_arm64.c | 199 ++++++++++++++++++
.../arm64/kernel/probes/optprobe_trampoline.S | 97 +++++++++
include/linux/kprobes.h | 2 +
kernel/kprobes.c | 22 ++
7 files changed, 344 insertions(+)
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 c4207cf9bb17..6b68ec498e67 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -200,6 +200,7 @@ config ARM64
select HAVE_STACKPROTECTOR
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_KPROBES
+ select HAVE_OPTPROBES
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 05cd82eeca13..3838e4317877 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -39,6 +39,27 @@ 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);
+
+struct arch_optimized_insn {
+ kprobe_opcode_t orig_insn[1];
+ kprobe_opcode_t *trampoline;
+};
+
+#define MAX_OPTIMIZED_LENGTH sizeof(kprobe_opcode_t)
+#define MAX_OPTINSN_SIZE \
+ ((unsigned long)optprobe_template_restore_end - (unsigned long)optprobe_template_entry)
+
+extern __visible kprobe_opcode_t optprobe_template_entry[];
+extern __visible kprobe_opcode_t optprobe_template_val[];
+extern __visible kprobe_opcode_t optprobe_template_common[];
+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[];
+extern __visible kprobe_opcode_t optinsn_slot[];
+
+void optprobe_common(void);
+
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 8e4be92e25b1..07105fd3261d 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/opt_arm64.c b/arch/arm64/kernel/probes/opt_arm64.c
new file mode 100644
index 000000000000..1bad5cddcdf2
--- /dev/null
+++ b/arch/arm64/kernel/probes/opt_arm64.c
@@ -0,0 +1,199 @@
+// 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/compiler.h>
+#include <asm/insn.h>
+#include <asm/kprobes.h>
+#include <asm/patching.h>
+
+#define OPTPROBE_BATCH_SIZE 64
+#define GET_LO_VAL(val) FIELD_GET(GENMASK(31, 0), val)
+#define GET_HI_VAL(val) FIELD_GET(GENMASK(63, 32), val)
+
+#define TMPL_VAL_IDX \
+ (optprobe_template_val - optprobe_template_entry)
+#define TMPL_CALL_COMMON \
+ (optprobe_template_common - 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)
+#define TMPL_END_IDX \
+ (optprobe_template_end - optprobe_template_entry)
+
+static bool insn_page_in_use;
+
+void *alloc_optinsn_page(void)
+{
+ if (insn_page_in_use)
+ return NULL;
+ insn_page_in_use = true;
+ return &optinsn_slot;
+}
+
+void free_optinsn_page(void *page)
+{
+ insn_page_in_use = false;
+}
+
+int arch_check_optimized_kprobe(struct optimized_kprobe *op)
+{
+ return 0;
+}
+
+int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
+{
+ return optinsn->trampoline != NULL;
+}
+
+int arch_within_optimized_kprobe(struct optimized_kprobe *op, kprobe_opcode_t *addr)
+{
+ return op->kp.addr == addr;
+}
+
+static void optprobe_set_pc_value(struct optimized_kprobe *op, struct pt_regs *regs)
+{
+ regs->pc = (unsigned long)op->kp.addr;
+}
+
+static int optprobe_check_branch_limit(unsigned long pc, unsigned long addr)
+{
+ long offset;
+
+ if ((pc & 0x3) || (addr & 0x3))
+ return -ERANGE;
+
+ offset = (long)addr - (long)pc;
+ if (offset < -SZ_128M || offset >= SZ_128M)
+ return -ERANGE;
+
+ return 0;
+}
+
+int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
+{
+ kprobe_opcode_t *code, *buf;
+ u32 insn;
+ int ret = -ENOMEM;
+ int i;
+
+ buf = kcalloc(MAX_OPTINSN_SIZE, sizeof(kprobe_opcode_t), GFP_KERNEL);
+ if (!buf)
+ return ret;
+
+ code = get_optinsn_slot();
+ if (!code)
+ goto out;
+
+ if (optprobe_check_branch_limit((unsigned long)code, (unsigned long)orig->addr + 8)) {
+ ret = -ERANGE;
+ goto error;
+ }
+
+ op->set_pc = optprobe_set_pc_value;
+ memcpy(buf, optprobe_template_entry, MAX_OPTINSN_SIZE * sizeof(kprobe_opcode_t));
+
+ insn = aarch64_insn_gen_branch_imm((unsigned long)&code[TMPL_CALL_COMMON],
+ (unsigned long)&optprobe_common,
+ AARCH64_INSN_BRANCH_LINK);
+ buf[TMPL_CALL_COMMON] = insn;
+
+ insn = aarch64_insn_gen_branch_imm((unsigned long)&code[TMPL_RESTORE_END],
+ (unsigned long)op->kp.addr + 4,
+ AARCH64_INSN_BRANCH_NOLINK);
+ buf[TMPL_RESTORE_END] = insn;
+
+ buf[TMPL_VAL_IDX] = cpu_to_le32(GET_LO_VAL((unsigned long)op));
+ buf[TMPL_VAL_IDX + 1] = cpu_to_le32(GET_HI_VAL((unsigned long)op));
+ buf[TMPL_RESTORE_ORIGN_INSN] = orig->opcode;
+
+ /* Setup template */
+ for (i = 0; i < MAX_OPTINSN_SIZE; i++)
+ aarch64_insn_patch_text_nosync(code + i, buf[i]);
+
+ flush_icache_range((unsigned long)code, (unsigned long)(&code[TMPL_VAL_IDX]));
+ /* Set op->optinsn.trampoline means prepared. */
+ op->optinsn.trampoline = code;
+
+out:
+ kfree(buf);
+ return ret;
+
+error:
+ free_optinsn_slot(code, 0);
+ goto out;
+}
+
+void arch_optimize_kprobes(struct list_head *oplist)
+{
+ struct optimized_kprobe *op, *tmp;
+ kprobe_opcode_t insns[OPTPROBE_BATCH_SIZE];
+ void *addrs[OPTPROBE_BATCH_SIZE];
+ int i = 0;
+
+ list_for_each_entry_safe(op, tmp, oplist, list) {
+ WARN_ON(kprobe_disabled(&op->kp));
+
+ /*
+ * Backup instructions which will be replaced
+ * by jump address
+ */
+ memcpy(op->optinsn.orig_insn, op->kp.addr, AARCH64_INSN_SIZE);
+
+ addrs[i] = (void *)op->kp.addr;
+ insns[i] = aarch64_insn_gen_branch_imm((unsigned long)op->kp.addr,
+ (unsigned long)op->optinsn.trampoline,
+ AARCH64_INSN_BRANCH_NOLINK);
+
+ list_del_init(&op->list);
+ if (++i == OPTPROBE_BATCH_SIZE)
+ break;
+ }
+
+ aarch64_insn_patch_text(addrs, insns, i);
+}
+
+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;
+ kprobe_opcode_t insns[OPTPROBE_BATCH_SIZE];
+ void *addrs[OPTPROBE_BATCH_SIZE];
+ int i = 0;
+
+ list_for_each_entry_safe(op, tmp, oplist, list) {
+ addrs[i] = (void *)op->kp.addr;
+ insns[i] = BRK64_OPCODE_KPROBES;
+ list_move(&op->list, done_list);
+
+ if (++i == OPTPROBE_BATCH_SIZE)
+ break;
+ }
+
+ aarch64_insn_patch_text(addrs, insns, i);
+}
+
+void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
+{
+ if (op->optinsn.trampoline) {
+ free_optinsn_slot(op->optinsn.trampoline, 1);
+ op->optinsn.trampoline = NULL;
+ }
+}
diff --git a/arch/arm64/kernel/probes/optprobe_trampoline.S b/arch/arm64/kernel/probes/optprobe_trampoline.S
new file mode 100644
index 000000000000..1376daeae844
--- /dev/null
+++ b/arch/arm64/kernel/probes/optprobe_trampoline.S
@@ -0,0 +1,97 @@
+/* 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>
+
+#define OPT_SLOT_SIZE 65536
+
+ .global optinsn_slot
+optinsn_slot:
+ .space OPT_SLOT_SIZE
+
+SYM_CODE_START(optprobe_common)
+ 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 x2, sp, #PT_REGS_SIZE
+ str x2, [sp, #S_SP]
+ /* Construct a useful saved PSTATE */
+ mrs x2, nzcv
+ mrs x3, daif
+ orr x2, x2, x3
+ mrs x3, CurrentEL
+ orr x2, x2, x3
+ mrs x3, SPSel
+ orr x2, x2, x3
+ stp xzr, x2, [sp, #S_PC]
+
+ /* set the pt_regs address to x1 */
+ mov x1, sp
+ /* store lr of optprobe_common temporary */
+ sub sp, sp, #0x10
+ str lr, [sp, #0x8]
+
+ bl optprobe_optimized_callback
+
+ ldr lr, [sp, #0x8]
+ add sp, sp, #0x10
+ 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]
+ ret
+SYM_CODE_END(optprobe_common)
+
+ .global optprobe_template_entry
+optprobe_template_entry:
+ sub sp, sp, #PT_REGS_SIZE
+ str lr, [sp, #S_LR]
+ stp x0, x1, [sp, #S_X0]
+ /* Get parameters to optimized_callback() */
+ ldr x0, 1f
+ .global optprobe_template_common
+optprobe_template_common:
+ nop
+ 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_val
+optprobe_template_val:
+ 1: .long 0
+ .long 0
+ .global optprobe_template_end
+optprobe_template_end:
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 8c8f7a4d93af..7be680155df7 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -329,6 +329,7 @@ struct optimized_kprobe {
struct kprobe kp;
struct list_head list; /* list for optimizing queue */
struct arch_optimized_insn optinsn;
+ void (*set_pc)(struct optimized_kprobe *op, struct pt_regs *regs);
};

/* Architecture dependent functions for direct jump optimization */
@@ -345,6 +346,7 @@ extern int arch_within_optimized_kprobe(struct optimized_kprobe *op,
kprobe_opcode_t *addr);

extern void opt_pre_handler(struct kprobe *p, struct pt_regs *regs);
+extern void optprobe_optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs);

DEFINE_INSN_CACHE_OPS(optinsn);

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 21eccc961bba..d799e562a39a 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -430,6 +430,28 @@ void opt_pre_handler(struct kprobe *p, struct pt_regs *regs)
}
NOKPROBE_SYMBOL(opt_pre_handler);

+void optprobe_optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
+{
+ if (kprobe_disabled(&op->kp))
+ return;
+
+ preempt_disable();
+
+ if (kprobe_running()) {
+ kprobes_inc_nmissed_count(&op->kp);
+ } else {
+ op->set_pc(op, regs);
+ __this_cpu_write(current_kprobe, &op->kp);
+ get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+ opt_pre_handler(&op->kp, regs);
+ __this_cpu_write(current_kprobe, NULL);
+ }
+
+ preempt_enable();
+}
+NOKPROBE_SYMBOL(optprobe_optimized_callback)
+
+
/* Free optimized instructions and optimized_kprobe */
static void free_aggr_kprobe(struct kprobe *p)
{
--
2.33.0
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