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Subject[PATCH v10 2/2] ARM: kprobes: enable OPTPROBES for ARM 32
Date
This patch introduce kprobeopt for ARM 32.

Limitations:
- Currently only kernel compiled with ARM ISA is supported.

- Offset between probe point and optinsn slot must not larger than
32MiB. Masami Hiramatsu suggests replacing 2 words, it will make
things complex. Futher patch can make such optimization.

Kprobe opt on ARM is relatively simpler than kprobe opt on x86 because
ARM instruction is always 4 bytes aligned and 4 bytes long. This patch
replace probed instruction by a 'b', branch to trampoline code and then
calls optimized_callback(). optimized_callback() calls opt_pre_handler()
to execute kprobe handler. It also emulate/simulate replaced instruction.

When unregistering kprobe, the deferred manner of unoptimizer may leave
branch instruction before optimizer is called. Different from x86_64,
which only copy the probed insn after optprobe_template_end and
reexecute them, this patch call singlestep to emulate/simulate the insn
directly. Futher patch can optimize this behavior.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Jon Medhurst (Tixy) <tixy@linaro.org>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>

---

v1 -> v2:

- Improvement: if replaced instruction is conditional, generate a
conditional branch instruction for it;

- Introduces RELATIVEJUMP_OPCODES due to ARM kprobe_opcode_t is 4
bytes;

- Removes size field in struct arch_optimized_insn;

- Use arm_gen_branch() to generate branch instruction;

- Remove all recover logic: ARM doesn't use tail buffer, no need
recover replaced instructions like x86;

- Remove incorrect CONFIG_THUMB checking;

- can_optimize() always returns true if address is well aligned;

- Improve optimized_callback: using opt_pre_handler();

- Bugfix: correct range checking code and improve comments;

- Fix commit message.

v2 -> v3:

- Rename RELATIVEJUMP_OPCODES to MAX_COPIED_INSNS;

- Remove unneeded checking:
arch_check_optimized_kprobe(), can_optimize();

- Add missing flush_icache_range() in arch_prepare_optimized_kprobe();

- Remove unneeded 'return;'.

v3 -> v4:

- Use __mem_to_opcode_arm() to translate copied_insn to ensure it
works in big endian kernel;

- Replace 'nop' placeholder in trampoline code template with
'.long 0' to avoid confusion: reader may regard 'nop' as an
instruction, but it is value in fact.

v4 -> v5:

- Don't optimize stack store operations.

- Introduce prepared field to arch_optimized_insn to indicate whether
it is prepared. Similar to size field with x86. See v1 -> v2.

v5 -> v6:

- Dynamically reserve stack according to instruction.

- Rename: kprobes-opt.c -> kprobes-opt-arm.c.

- Set op->optinsn.insn after all works are done.

v6 -> v7:

- Using checker to check stack consumption.

v7 -> v8:

- Small code adjustments.

v8 -> v9:

- Utilize original kprobe passed to arch_prepare_optimized_kprobe()
to avoid copy ainsn twice.

- A bug in arch_prepare_optimized_kprobe() is found and fixed.

v9 -> v10:

- Commit message improvements.
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/kprobes.h | 26 ++++
arch/arm/kernel/Makefile | 3 +-
arch/arm/kernel/kprobes-opt-arm.c | 290 ++++++++++++++++++++++++++++++++++++++
4 files changed, 319 insertions(+), 1 deletion(-)
create mode 100644 arch/arm/kernel/kprobes-opt-arm.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 89c4b5c..8281cea 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -59,6 +59,7 @@ config ARM
select HAVE_MEMBLOCK
select HAVE_MOD_ARCH_SPECIFIC if ARM_UNWIND
select HAVE_OPROFILE if (HAVE_PERF_EVENTS)
+ select HAVE_OPTPROBES if (!THUMB2_KERNEL)
select HAVE_PERF_EVENTS
select HAVE_PERF_REGS
select HAVE_PERF_USER_STACK_DUMP
diff --git a/arch/arm/include/asm/kprobes.h b/arch/arm/include/asm/kprobes.h
index 56f9ac6..c1016cb 100644
--- a/arch/arm/include/asm/kprobes.h
+++ b/arch/arm/include/asm/kprobes.h
@@ -50,5 +50,31 @@ int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
int kprobe_exceptions_notify(struct notifier_block *self,
unsigned long val, void *data);

+/* 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;
+
+#define MAX_OPTIMIZED_LENGTH (4)
+#define MAX_OPTINSN_SIZE \
+ (((unsigned long)&optprobe_template_end - \
+ (unsigned long)&optprobe_template_entry))
+#define RELATIVEJUMP_SIZE (4)
+
+struct arch_optimized_insn {
+ /*
+ * copy of the original instructions.
+ * Different from x86, ARM kprobe_opcode_t is u32.
+ */
+#define MAX_COPIED_INSN ((RELATIVEJUMP_SIZE) / sizeof(kprobe_opcode_t))
+ kprobe_opcode_t copied_insn[MAX_COPIED_INSN];
+ /* detour code buffer */
+ kprobe_opcode_t *insn;
+ /*
+ * we always copies one instruction on arm32,
+ * size always be 4, so no size field.
+ */
+};

#endif /* _ARM_KPROBES_H */
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 45aed4b..8a16fcf 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -52,11 +52,12 @@ obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o insn.o
obj-$(CONFIG_JUMP_LABEL) += jump_label.o insn.o patch.o
obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o
obj-$(CONFIG_UPROBES) += probes.o probes-arm.o uprobes.o uprobes-arm.o
-obj-$(CONFIG_KPROBES) += probes.o kprobes.o kprobes-common.o patch.o probes-checkers-common.o
+obj-$(CONFIG_KPROBES) += probes.o kprobes.o kprobes-common.o patch.o probes-checkers-common.o insn.o
ifdef CONFIG_THUMB2_KERNEL
obj-$(CONFIG_KPROBES) += kprobes-thumb.o probes-thumb.o probes-checkers-thumb.o
else
obj-$(CONFIG_KPROBES) += kprobes-arm.o probes-arm.o probes-checkers-arm.o
+obj-$(CONFIG_OPTPROBES) += kprobes-opt-arm.o
endif
obj-$(CONFIG_ARM_KPROBES_TEST) += test-kprobes.o
test-kprobes-objs := kprobes-test.o
diff --git a/arch/arm/kernel/kprobes-opt-arm.c b/arch/arm/kernel/kprobes-opt-arm.c
new file mode 100644
index 0000000..f9d213c
--- /dev/null
+++ b/arch/arm/kernel/kprobes-opt-arm.c
@@ -0,0 +1,290 @@
+/*
+ * Kernel Probes Jump Optimization (Optprobes)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2002, 2004
+ * Copyright (C) Hitachi Ltd., 2012
+ * Copyright (C) Huawei Inc., 2014
+ */
+
+#include <linux/kprobes.h>
+#include <linux/jump_label.h>
+#include <asm/kprobes.h>
+#include <asm/cacheflush.h>
+/* for arm_gen_branch */
+#include "insn.h"
+/* for patch_text */
+#include "patch.h"
+
+/*
+ * NOTE: the first sub and add instruction will be modified according
+ * to the stack cost of the instruction.
+ */
+asm (
+ ".global optprobe_template_entry\n"
+ "optprobe_template_entry:\n"
+ " sub sp, sp, #0xff\n"
+ " stmia sp, {r0 - r14} \n"
+ " add r3, sp, #0xff\n"
+ " str r3, [sp, #52]\n"
+ " mrs r4, cpsr\n"
+ " str r4, [sp, #64]\n"
+ " mov r1, sp\n"
+ " ldr r0, 1f\n"
+ " ldr r2, 2f\n"
+ " blx r2\n"
+ " ldr r1, [sp, #64]\n"
+ " msr cpsr_fs, r1\n"
+ " ldmia sp, {r0 - r15}\n"
+ ".global optprobe_template_val\n"
+ "optprobe_template_val:\n"
+ "1: .long 0\n"
+ ".global optprobe_template_call\n"
+ "optprobe_template_call:\n"
+ "2: .long 0\n"
+ ".global optprobe_template_end\n"
+ "optprobe_template_end:\n");
+
+#define TMPL_VAL_IDX \
+ ((long)&optprobe_template_val - (long)&optprobe_template_entry)
+#define TMPL_CALL_IDX \
+ ((long)&optprobe_template_call - (long)&optprobe_template_entry)
+#define TMPL_END_IDX \
+ ((long)&optprobe_template_end - (long)&optprobe_template_entry)
+
+/*
+ * ARM can always optimize an instruction when using ARM ISA, except
+ * instructions like 'str r0, [sp, r1]' which store to stack and unable
+ * to determine stack space consumption statically.
+ */
+int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
+{
+ return optinsn->insn != NULL;
+}
+
+/*
+ * In ARM ISA, kprobe opt always replace one instruction (4 bytes
+ * aligned and 4 bytes long). It is impossiable to encounter another
+ * kprobe in the address range. So always return 0.
+ */
+int arch_check_optimized_kprobe(struct optimized_kprobe *op)
+{
+ return 0;
+}
+
+/* Caller must ensure addr & 3 == 0 */
+static int can_optimize(struct kprobe *kp)
+{
+ if (kp->ainsn.stack_space < 0)
+ return 0;
+ /*
+ * 255 is the biggest imm can be used in 'sub r0, r0, #<imm>'.
+ * Number larger than 255 needs special encoding.
+ */
+ if (kp->ainsn.stack_space > 255 - sizeof(struct pt_regs))
+ return 0;
+ return 1;
+}
+
+/* Free optimized instruction slot */
+static void
+__arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
+{
+ if (op->optinsn.insn) {
+ free_optinsn_slot(op->optinsn.insn, dirty);
+ op->optinsn.insn = NULL;
+ }
+}
+
+extern void kprobe_handler(struct pt_regs *regs);
+
+static void
+optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
+{
+ unsigned long flags;
+ struct kprobe *p = &op->kp;
+ struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+
+ /* Save skipped registers */
+ regs->ARM_pc = (unsigned long)op->kp.addr;
+ regs->ARM_ORIG_r0 = ~0UL;
+
+ local_irq_save(flags);
+
+ if (kprobe_running()) {
+ kprobes_inc_nmissed_count(&op->kp);
+ } else {
+ __this_cpu_write(current_kprobe, &op->kp);
+ kcb->kprobe_status = KPROBE_HIT_ACTIVE;
+ opt_pre_handler(&op->kp, regs);
+ __this_cpu_write(current_kprobe, NULL);
+ }
+
+ /* In each case, we must singlestep the replaced instruction. */
+ op->kp.ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
+
+ local_irq_restore(flags);
+}
+
+int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *orig)
+{
+ u8 *buf;
+ unsigned long *code;
+ unsigned long rel_chk;
+ unsigned long val;
+ unsigned long stack_protect = sizeof(struct pt_regs);
+
+ if (!can_optimize(orig))
+ return -EILSEQ;
+
+ buf = (u8 *)get_optinsn_slot();
+ if (!buf)
+ return -ENOMEM;
+
+ /*
+ * Verify if the address gap is in 32MiB 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 28 27 24 23 0
+ * +------+---+---+---+---+----------------+
+ * | cond | 1 | 0 | 1 | 0 | imm24 |
+ * +------+---+---+---+---+----------------+
+ *
+ * imm24 is a signed 24 bits integer. The real branch offset is computed
+ * by: imm32 = SignExtend(imm24:'00', 32);
+ *
+ * So the maximum forward branch should be:
+ * (0x007fffff << 2) = 0x01fffffc = 0x1fffffc
+ * The maximum backword branch should be:
+ * (0xff800000 << 2) = 0xfe000000 = -0x2000000
+ *
+ * We can simply check (rel & 0xfe000003):
+ * if rel is positive, (rel & 0xfe000000) shoule be 0
+ * if rel is negitive, (rel & 0xfe000000) should be 0xfe000000
+ * the last '3' is used for alignment checking.
+ */
+ rel_chk = (unsigned long)((long)buf -
+ (long)orig->addr + 8) & 0xfe000003;
+
+ if ((rel_chk != 0) && (rel_chk != 0xfe000000)) {
+ /*
+ * Different from x86, we free buf directly instead of
+ * calling __arch_remove_optimized_kprobe() because
+ * we have not fill any field in op.
+ */
+ free_optinsn_slot((kprobe_opcode_t *)buf, 0);
+ return -ERANGE;
+ }
+
+ /* Copy arch-dep-instance from template. */
+ memcpy(buf, &optprobe_template_entry, TMPL_END_IDX);
+
+ /* Adjust buffer according to instruction. */
+ BUG_ON(orig->ainsn.stack_space < 0);
+ stack_protect += orig->ainsn.stack_space;
+
+ /* Should have been filtered by can_optimize(). */
+ BUG_ON(stack_protect > 255);
+
+ /* Create a 'sub sp, sp, #<stack_protect>' */
+ code = (unsigned long *)(buf);
+ code[0] = __opcode_to_mem_arm(0xe24dd000 | stack_protect);
+ /* Create a 'add r3, sp, #<stack_protect>' */
+ code[2] = __opcode_to_mem_arm(0xe28d3000 | stack_protect);
+
+ /* Set probe information */
+ val = (unsigned long)op;
+ memcpy(buf + TMPL_VAL_IDX, &val, sizeof(val));
+
+ /* Set probe function call */
+ val = (unsigned long)optimized_callback;
+ memcpy(buf + TMPL_CALL_IDX, &val, sizeof(val));
+
+ flush_icache_range((unsigned long)buf,
+ (unsigned long)buf + TMPL_END_IDX);
+
+ /* Set op->optinsn.insn means prepared */
+ op->optinsn.insn = (kprobe_opcode_t *)buf;
+ return 0;
+}
+
+void arch_optimize_kprobes(struct list_head *oplist)
+{
+ struct optimized_kprobe *op, *tmp;
+
+ list_for_each_entry_safe(op, tmp, oplist, list) {
+ unsigned long 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 = arm_gen_branch((unsigned long)op->kp.addr,
+ (unsigned long)op->optinsn.insn);
+ BUG_ON(insn == 0);
+
+ /*
+ * Make it a conditional branch if replaced insn
+ * is consitional
+ */
+ insn = (__mem_to_opcode_arm(
+ op->optinsn.copied_insn[0]) & 0xf0000000) |
+ (insn & 0x0fffffff);
+
+ patch_text(op->kp.addr, insn);
+
+ 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);
+ }
+}
+
+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);
+}
+
+void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
+{
+ __arch_remove_optimized_kprobe(op, 1);
+}
--
1.8.4


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