[PATCH v3 2/2] arm64: kprobe: Enable OPTPROBE for arm64
From: Qi Liu
Date: Tue Aug 10 2021 - 05:18:07 EST
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.
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
Note:
To guarantee the offset between probe point and kprobe pre_handler
is smaller than 128MiB, users should set
CONFIG_RANDOMIZE_MODULE_REGION_FULL=N or set nokaslr in command line, or
optprobe will not work and fall back to normal kprobe.
Signed-off-by: Qi Liu <liuqi115@xxxxxxxxxx>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/kprobes.h | 24 ++
arch/arm64/kernel/probes/Makefile | 2 +
arch/arm64/kernel/probes/kprobes.c | 19 +-
arch/arm64/kernel/probes/opt_arm64.c | 239 ++++++++++++++++++
.../arm64/kernel/probes/optprobe_trampoline.S | 37 +++
6 files changed, 319 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 b5b13a932561..b05d1d275d87 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 5d38ff4a4806..6b2fdd2ad7d8 100644
--- a/arch/arm64/include/asm/kprobes.h
+++ b/arch/arm64/include/asm/kprobes.h
@@ -39,6 +39,30 @@ 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[];
+extern __visible kprobe_opcode_t optprobe_template_max_length[];
+
+#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 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/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 6dbcc89f6662..83755ad62abe 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -11,6 +11,7 @@
#include <linux/kasan.h>
#include <linux/kernel.h>
#include <linux/kprobes.h>
+#include <linux/moduleloader.h>
#include <linux/sched/debug.h>
#include <linux/set_memory.h>
#include <linux/slab.h>
@@ -113,9 +114,21 @@ 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 000000000000..d59b6a31a005
--- /dev/null
+++ b/arch/arm64/kernel/probes/opt_arm64.c
@@ -0,0 +1,239 @@
+// 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/insn.h>
+#include <asm/kprobes.h>
+#include <asm/patching.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)
+#define TMPL_MAX_LENGTH \
+ (optprobe_template_max_length - 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)
+
+static bool is_offset_in_range(unsigned long start, unsigned long end)
+{
+ long offset = end - start;
+
+ /*
+ * 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) = 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.
+ */
+ return (offset >= -0x8000000 && offset <= 0x7fffffc && !(offset & 0x3));
+}
+
+int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
+ struct kprobe *orig)
+{
+ kprobe_opcode_t *code, *buf;
+ void **addrs;
+ u32 insn;
+ int ret, i;
+
+ addrs = kcalloc(TMPL_MAX_LENGTH, sizeof(void *), GFP_KERNEL);
+ if (!addrs)
+ return -ENOMEM;
+
+ buf = kcalloc(TMPL_MAX_LENGTH, sizeof(kprobe_opcode_t), GFP_KERNEL);
+ if (!buf) {
+ kfree(addrs);
+ return -ENOMEM;
+ }
+
+ code = get_optinsn_slot();
+ if (!code) {
+ kfree(addrs);
+ kfree(buf);
+ return -ENOMEM;
+ }
+
+ if (!is_offset_in_range((unsigned long)code,
+ (unsigned long)orig->addr + 8)) {
+ ret = -ERANGE;
+ goto error;
+ }
+
+ if (!is_offset_in_range((unsigned long)code + TMPL_CALL_BACK,
+ (unsigned long)optimized_callback)) {
+ ret = -ERANGE;
+ goto error;
+ }
+
+ if (!is_offset_in_range((unsigned long)&code[TMPL_RESTORE_END],
+ (unsigned long)op->kp.addr + 4)) {
+ ret = -ERANGE;
+ goto error;
+ }
+
+ memcpy(buf, optprobe_template_entry,
+ TMPL_END_IDX * sizeof(kprobe_opcode_t));
+
+ buf[TMPL_VAL_IDX] = FIELD_GET(GENMASK(31, 0), (unsigned long long)op);
+ buf[TMPL_VAL_IDX + 1] =
+ FIELD_GET(GENMASK(63, 32), (unsigned long long)op);
+ buf[TMPL_RESTORE_ORIGN_INSN] = orig->opcode;
+
+ insn = aarch64_insn_gen_branch_imm(
+ (unsigned long)(&code[TMPL_CALL_BACK]),
+ (unsigned long)optimized_callback, AARCH64_INSN_BRANCH_LINK);
+ buf[TMPL_CALL_BACK] = 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;
+
+ /* Setup template */
+ for (i = 0; i < TMPL_MAX_LENGTH; i++)
+ addrs[i] = code + i;
+
+ ret = aarch64_insn_patch_text(addrs, buf, TMPL_MAX_LENGTH);
+ if (ret < 0)
+ goto error;
+
+ flush_icache_range((unsigned long)code,
+ (unsigned long)(&code[TMPL_END_IDX]));
+
+ /* Set op->optinsn.insn means prepared. */
+ op->optinsn.insn = code;
+
+out:
+ kfree(addrs);
+ 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;
+
+ 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 000000000000..24d713d400cd
--- /dev/null
+++ b/arch/arm64/kernel/probes/optprobe_trampoline.S
@@ -0,0 +1,37 @@
+/* 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
+ save_all_base_regs
+ /* Get parameters to optimized_callback() */
+ ldr x0, 1f
+ mov x1, sp
+ /* Branch to optimized_callback() */
+ .global optprobe_template_call
+optprobe_template_call:
+ nop
+ restore_all_base_regs
+ 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
+ .global optprobe_template_max_length
+optprobe_template_max_length:
--
2.17.1