Re: [RFC PATCH v3 2/3] arch/powerpc : optprobes for powerpc core

[Masami Hiramatsu]

On Tue, 31 May 2016 16:26:30 +0530
Anju T <anju@xxxxxxxxxxxxxxxxxx> wrote:

> Instructions which can be emulated are suppliants for
> optimization. Before optimization ensure that the address range
> between the detour buffer allocated and the instruction being probed
> is within +/- 32MB.
> 
> Signed-off-by: Anju T <anju@xxxxxxxxxxxxxxxxxx>
> ---
>  arch/powerpc/kernel/optprobes.c | 351 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 351 insertions(+)
>  create mode 100644 arch/powerpc/kernel/optprobes.c
> 
> diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
> new file mode 100644
> index 0000000..c4253b6
> --- /dev/null
> +++ b/arch/powerpc/kernel/optprobes.c
> @@ -0,0 +1,351 @@
> +/*
> + * Code for Kernel probes Jump optimization.
> + *
> + * Copyright 2016, Anju T, IBM Corp.
> + *
> + * 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.
> + */
> +
> +#include <linux/kprobes.h>
> +#include <linux/jump_label.h>
> +#include <linux/types.h>
> +#include <linux/slab.h>
> +#include <linux/list.h>
> +#include <asm/kprobes.h>
> +#include <asm/ptrace.h>
> +#include <asm/cacheflush.h>
> +#include <asm/code-patching.h>
> +#include <asm/sstep.h>
> +
> +DEFINE_INSN_CACHE_OPS(ppc_optinsn)
> +
> +#define TMPL_CALL_HDLR_IDX	\
> +	(optprobe_template_call_handler - optprobe_template_entry)
> +#define TMPL_EMULATE_IDX	\
> +	(optprobe_template_call_emulate - optprobe_template_entry)
> +#define TMPL_RET_BRANCH_IDX	\
> +	(optprobe_template_ret_branch - optprobe_template_entry)
> +#define TMPL_RET_IDX	\
> +	(optprobe_template_ret - optprobe_template_entry)
> +#define TMPL_KP_IDX	\
> +	(optprobe_template_kp_addr - optprobe_template_entry)
> +#define TMPL_OP1_IDX	\
> +	(optprobe_template_op_address1 - optprobe_template_entry)
> +#define TMPL_OP2_IDX	\
> +	(optprobe_template_op_address2 - optprobe_template_entry)
> +#define TMPL_INSN_IDX	\
> +	(optprobe_template_insn - optprobe_template_entry)
> +#define TMPL_END_IDX	\
> +	(optprobe_template_end - optprobe_template_entry)
> +
> +static unsigned long val_nip;
> +
> +static void *__ppc_alloc_insn_page(void)
> +{
> +	return &optinsn_slot;
> +}
> +
> +static void *__ppc_free_insn_page(void *page __maybe_unused)
> +{
> +	return;
> +}

Hmm, you should not return optinsn_slot twice or more, because
it actually doesn't allocate memory but just returns reserved
memory area. So, it should be something like this;

static bool insn_page_in_use;

static void *__ppc_alloc_insn_page(void)
{
	if (insn_page_in_use)
		return NULL;
	insn_page_in_use = true;
	return &optinsn_slot;
}

static void *__ppc_free_insn_page(void *page __maybe_unused)
{
	insn_page_in_use = false;
}


> +
> +struct kprobe_insn_cache kprobe_ppc_optinsn_slots = {
> +	.mutex = __MUTEX_INITIALIZER(kprobe_ppc_optinsn_slots.mutex),
> +	.pages = LIST_HEAD_INIT(kprobe_ppc_optinsn_slots.pages),
> +	/* insn_size initialized later */
> +	.alloc = __ppc_alloc_insn_page,
> +	.free = __ppc_free_insn_page,
> +	.nr_garbage = 0,
> +};
> +
> +kprobe_opcode_t *ppc_get_optinsn_slot(struct optimized_kprobe *op)
> +{
> +	/*
> +	 * The insn slot is allocated from the reserved
> +	 * area(ie &optinsn_slot).We are not optimizing probes
> +	 * at module_addr now.
> +	 */
> +	kprobe_opcode_t *slot = NULL;
> +
> +	if (is_kernel_addr(op->kp.addr))
> +		slot = get_ppc_optinsn_slot();
> +	return slot;
> +}
> +
> +static void ppc_free_optinsn_slot(struct optimized_kprobe *op)
> +{
> +	if (!op->optinsn.insn)
> +		return;
> +	if (is_kernel_addr((unsigned long)op->kp.addr))
> +		free_ppc_optinsn_slot(op->optinsn.insn, 0);
> +}
> +
> +static void
> +__arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
> +{
> +	ppc_free_optinsn_slot(op);
> +	op->optinsn.insn = NULL;
> +}
> +
> +static int can_optimize(struct kprobe *p)
> +{
> +	struct pt_regs *regs;
> +	unsigned int instr;
> +	int r;
> +
> +	/*
> +	 * Not optimizing the kprobe placed by
> +	 * kretprobe during boot time
> +	 */
> +	if ((kprobe_opcode_t)p->addr == (kprobe_opcode_t)&kretprobe_trampoline)
> +		return 0;
> +
> +	regs = kmalloc(sizeof(*regs), GFP_KERNEL);
> +	if (!regs)
> +		return -ENOMEM;
> +	memset(regs, 0, sizeof(struct pt_regs));
> +	memcpy(regs, current_pt_regs(), sizeof(struct pt_regs));
> +	regs->nip = p->addr;
> +	instr = *(p->ainsn.insn);
> +
> +	/* Ensure the instruction can be emulated*/
> +	r = emulate_step(regs, instr);
> +	val_nip = regs->nip;
> +	if (r != 1)
> +		return 0;
> +
> +	return 1;
> +}
> +
> +static void
> +create_return_branch(struct optimized_kprobe *op, struct pt_regs *regs)
> +{
> +	/*
> +	 * Create a branch back to the return address
> +	 * after the probed instruction is emulated
> +	 */
> +
> +	kprobe_opcode_t branch, *buff;
> +	unsigned long ret;
> +
> +	ret = regs->nip;
> +	buff = op->optinsn.insn;
> +	/*
> +	 * TODO: For conditional branch instructions, the return
> +	 * address may differ in SMP systems.This has to be addressed.
> +	 */
> +
> +	branch = create_branch((unsigned int *)buff + TMPL_RET_IDX,
> +			       (unsigned long)ret, 0);
> +	buff[TMPL_RET_IDX] = branch;
> +	isync();
> +}
> +
> +static void
> +optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +	unsigned long flags;
> +
> +	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);
> +	}
> +	local_irq_restore(flags);
> +}
> +NOKPROBE_SYMBOL(optimized_callback);
> +
> +void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
> +{
> +	 __arch_remove_optimized_kprobe(op, 1);
> +}
> +
> +void  create_insn(unsigned int insn, kprobe_opcode_t *addr)
> +{
> +	u32 instr, instr2;
> +
> +	/*
> +	 * emulate_step() requires insn to be emulated as
> +	 * second parameter. Hence r4 should be loaded
> +	 * with 'insn'.
> +	 * synthesize addis r4,0,(insn)@h
> +	 */
> +	instr = 0x3c000000 | 0x800000 | ((insn >> 16) & 0xffff);
> +	*addr++ = instr;
> +
> +	/* ori r4,r4,(insn)@l */
> +	instr2 = 0x60000000 | 0x40000 | 0x800000;
> +	instr2 = instr2 | (insn & 0xffff);
> +	*addr = instr2;
> +}
> +
> +void create_load_address_insn(unsigned long val, kprobe_opcode_t *addr)
> +{
> +	u32 instr1, instr2, instr3, instr4, instr5;
> +	/*
> +	 * Optimized_kprobe structure is required as a parameter
> +	 * for invoking optimized_callback() and create_return_branch()
> +	 * from detour buffer. Hence need to have a 64bit immediate
> +	 * load into r3.
> +	 *
> +	 * lis r3,(op)@highest
> +	 */
> +	instr1 = 0x3c000000 | 0x600000 | ((val >> 48) & 0xffff);
> +	*addr++ = instr1;
> +
> +	/* ori r3,r3,(op)@higher */
> +	instr2 = 0x60000000 | 0x30000 | 0x600000 | ((val >> 32) & 0xffff);
> +	*addr++ = instr2;
> +
> +	/* rldicr r3,r3,32,31 */
> +	instr3 = 0x78000004 | 0x30000 | 0x600000 | ((32 & 0x1f) << 11);
> +	instr3 = instr3 | ((31 & 0x1f) << 6) | ((32 & 0x20) >> 4);
> +	*addr++ = instr3;
> +
> +	/* oris r3,r3,(op)@h */
> +	instr4 = 0x64000000 |  0x30000 | 0x600000 | ((val >> 16) & 0xffff);
> +	*addr++ = instr4;
> +
> +	/* ori r3,r3,(op)@l */
> +	instr5 =  0x60000000 | 0x30000 | 0x600000 | (val & 0xffff);
> +	*addr = instr5;
> +}
> +
> +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
> +{
> +	kprobe_opcode_t *buff, branch, branch2, branch3;
> +	long rel_chk, ret_chk;
> +
> +	kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
> +	op->optinsn.insn = NULL;
> +
> +	if (!can_optimize(p))
> +		return -EILSEQ;
> +
> +	/* Allocate instruction slot for detour buffer*/
> +	buff = ppc_get_optinsn_slot(op);
> +	if (!buff)
> +		return -ENOMEM;
> +
> +	/*
> +	 * OPTPROBE use a 'b' instruction to branch to optinsn.insn.
> +	 *
> +	 * The target address has to be relatively nearby, to permit use
> +	 * of branch instruction in powerpc because the address is specified
> +	 * in an immediate field in the instruction opcode itself, ie 24 bits
> +	 * in the opcode specify the address. Therefore the address gap should
> +	 * be 32MB on either side of the current instruction.
> +	 */
> +	rel_chk = (long)buff - (unsigned long)p->addr;
> +	if (rel_chk < -0x2000000 || rel_chk > 0x1fffffc || rel_chk & 0x3) {
> +		ppc_free_optinsn_slot(op);
> +		return -ERANGE;
> +	}
> +	/* Check the return address is also within 32MB range */
> +	ret_chk = (long)(buff + TMPL_RET_IDX) - (unsigned long)val_nip;

No, please don't pass the "regs->nip" via hidden channel like as this val_nip
static local variable. Instead, you should run emulate_step() again here,
or, at least you must keep the address and compare it. I recommend former.


Thank you,

> +	if (ret_chk < -0x2000000 || ret_chk > 0x1fffffc || ret_chk & 0x3) {
> +		ppc_free_optinsn_slot(op);
> +		return -ERANGE;
> +	}
> +
> +	/* Do Copy arch specific instance from template*/
> +	memcpy(buff, optprobe_template_entry,
> +	       TMPL_END_IDX * sizeof(kprobe_opcode_t));
> +	create_load_address_insn((unsigned long)p->addr, buff + TMPL_KP_IDX);
> +	create_load_address_insn((unsigned long)op, buff + TMPL_OP1_IDX);
> +	create_load_address_insn((unsigned long)op, buff + TMPL_OP2_IDX);
> +
> +	/* Create a branch to the optimized_callback function */
> +	branch = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
> +			       (unsigned long)optimized_callback + 8,
> +				BRANCH_SET_LINK);
> +
> +	/* Place the branch instr into the trampoline */
> +	buff[TMPL_CALL_HDLR_IDX] = branch;
> +	create_insn(*(p->ainsn.insn), buff + TMPL_INSN_IDX);
> +
> +	/*Create a branch instruction into the emulate_step*/
> +	branch3 = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
> +				(unsigned long)emulate_step + 8,
> +				BRANCH_SET_LINK);
> +	buff[TMPL_EMULATE_IDX] = branch3;
> +
> +	/* Create a branch for jumping back*/
> +	branch2 = create_branch((unsigned int *)buff + TMPL_RET_BRANCH_IDX,
> +				(unsigned long)create_return_branch + 8,
> +				BRANCH_SET_LINK);
> +	buff[TMPL_RET_BRANCH_IDX] = branch2;
> +
> +	op->optinsn.insn = buff;
> +	smp_mb();
> +	return 0;
> +}
> +
> +int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
> +{
> +	return optinsn->insn;
> +}
> +
> +/*
> + * Here,kprobe opt always replace one instruction (4 bytes
> + * aligned and 4 bytes long). It is impossible to encounter another
> + * kprobe in the address range. So always return 0.
> + */
> +int arch_check_optimized_kprobe(struct optimized_kprobe *op)
> +{
> +	return 0;
> +}
> +
> +void arch_optimize_kprobes(struct list_head *oplist)
> +{
> +	struct optimized_kprobe *op;
> +	struct optimized_kprobe *tmp;
> +
> +	unsigned int branch;
> +
> +	list_for_each_entry_safe(op, tmp, oplist, list) {
> +		/*
> +		 * Backup instructions which will be replaced
> +		 *by jump address
> +		 */
> +		memcpy(op->optinsn.copied_insn, op->kp.addr,
> +		       RELATIVEJUMP_SIZE);
> +		branch = create_branch((unsigned int *)op->kp.addr,
> +					(unsigned long)op->optinsn.insn, 0);
> +		*op->kp.addr = branch;
> +		list_del_init(&op->list);
> +	}
> +}
> +
> +void arch_unoptimize_kprobe(struct optimized_kprobe *op)
> +{
> +	arch_arm_kprobe(&op->kp);
> +}
> +
> +void arch_unoptimize_kprobes(struct list_head *oplist,
> +			     struct list_head *done_list)
> +{
> +	struct optimized_kprobe *op;
> +	struct optimized_kprobe *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 0;
> +}
> -- 
> 2.1.0
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>