Re: [PATCH v9 2/2] ARM: kprobes: enable OPTPROBES for ARM 32
From: Masami Hiramatsu
Date: Wed Nov 19 2014 - 23:04:34 EST
(2014/11/19 15:50), Wang Nan wrote:
> 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.
The part of kprobes-related things looks good to me :)
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Will need to be reviewed by arm32 maintainers too.
>
> 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.
>
> Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> Cc: Jon Medhurst (Tixy) <tixy@xxxxxxxxxx>
> Cc: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> ---
> 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);
> +}
>
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/