Subject: [PATCH v8 2/2] ARM: kprobes: enable OPTPROBES for ARM 32

From: [email-masked] (Wang Nan)
Date: Wed, 19 Nov 2014 15:08:05 +0800

On 2014/11/18 14:32, 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.
> 
> 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.
> 
> Signed-off-by: Wang Nan <[email-masked]>
> Acked-by: Masami Hiramatsu <[email-masked]>
> Cc: Jon Medhurst (Tixy) <[email-masked]>
> Cc: Russell King - ARM Linux <[email-masked]>
> Cc: Will Deacon <[email-masked]>
> ---
>  arch/arm/Kconfig                  |   1 +
>  arch/arm/include/asm/kprobes.h    |  26 ++++
>  arch/arm/kernel/Makefile          |   3 +-
>  arch/arm/kernel/kprobes-opt-arm.c | 285 ++++++++++++++++++++++++++++++++++++++
>  4 files changed, 314 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..55eb3ea
> --- /dev/null
> +++ b/arch/arm/kernel/kprobes-opt-arm.c
> @@ -0,0 +1,285 @@
> +/*
> + *  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 optimized_kprobe *op)
> +{
> +	if (op->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 (op->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)
> +{
> +	u8 *buf;
> +	unsigned long *code;
> +	unsigned long rel_chk;
> +	unsigned long val;
> +	unsigned long stack_protect = sizeof(struct pt_regs);
> +
> +	if (!can_optimize(op))
> +		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)op->kp.addr + 8) & 0xfe000003;
> +
> +	if ((rel_chk != 0) && (rel_chk != 0xfe000000)) {
> +		__arch_remove_optimized_kprobe(op, 0);

Here is a bug. Different from x86_64, ARM code doesn't set op->optinsn.insn
here, so __arch_remove_optimized_kprobe won't do anything. In version 9 patch
series I fix this problem by calling free_optinsn_slot(buf, 0) directly.
However, I forgot to mention it in its commit message.

> +		return -ERANGE;
> +	}
> +
> +	/* Copy arch-dep-instance from template. */
> +	memcpy(buf, &optprobe_template_entry, TMPL_END_IDX);
> +
> +	/* Adjust buffer according to instruction. */
> +	BUG_ON(op->kp.ainsn.stack_space < 0);
> +	stack_protect += op->kp.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);
> +}
>