Subject: Re: [RFC PATCH v2 2/3] arch/powerpc : optprobes for powerpc core

From: Masami Hiramatsu <[email-masked]>
Date: Fri, 20 May 2016 21:37:30 +0900

Hi Anju,

Please see my comments below,

On Thu, 19 May 2016 20:40:39 +0530
Anju T <[email-masked]> wrote:

> ppc_get_optinsn_slot() and ppc_free_optinsn_slot() are
> geared towards the allocation and freeing of memory from 
> the area reserved for detour buffer.
> 
> Signed-off-by: Anju T <[email-masked]>
> ---
>  arch/powerpc/kernel/optprobes.c | 480 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 480 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..bb61e18
> --- /dev/null
> +++ b/arch/powerpc/kernel/optprobes.c
> @@ -0,0 +1,480 @@
> +/*
> + * 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 SLOT_SIZE 65536
> +#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_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)
> +
> +struct kprobe_ppc_insn_page {
> +	struct list_head list;
> +	kprobe_opcode_t *insns;	/* Page of instruction slots */
> +	struct kprobe_insn_cache *cache;
> +	int nused;
> +	int ngarbage;
> +	char slot_used[];
> +};
> +
> +#define PPC_KPROBE_INSN_PAGE_SIZE(slots)	\
> +	(offsetof(struct kprobe_ppc_insn_page, slot_used) +	\
> +	(sizeof(char) * (slots)))
> +
> +enum ppc_kprobe_slot_state {
> +	SLOT_CLEAN = 0,
> +	SLOT_DIRTY = 1,
> +	SLOT_USED = 2,
> +};
> +
> +static 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 is initialized later */
> +	.nr_garbage = 0,
> +};
> +
> +static int ppc_slots_per_page(struct kprobe_insn_cache *c)
> +{
> +	/*
> +	 * Here the #slots per page differs from x86 as we have
> +	 * only 64KB reserved.
> +	 */
> +	return SLOT_SIZE / (c->insn_size * sizeof(kprobe_opcode_t));
> +}
> +
> +/* Return 1 if all garbages are collected, otherwise 0. */
> +static int collect_one_slot(struct kprobe_ppc_insn_page *kip, int idx)
> +{
> +	kip->slot_used[idx] = SLOT_CLEAN;
> +	kip->nused--;
> +	return 0;
> +}
> +
> +static int collect_garbage_slots(struct kprobe_insn_cache *c)
> +{
> +	struct kprobe_ppc_insn_page *kip, *next;
> +
> +	/* Ensure no-one is interrupted on the garbages */
> +	synchronize_sched();
> +
> +	list_for_each_entry_safe(kip, next, &c->pages, list) {
> +		int i;
> +
> +		if (kip->ngarbage == 0)
> +			continue;
> +		kip->ngarbage = 0;	/* we will collect all garbages */
> +		for (i = 0; i < ppc_slots_per_page(c); i++) {
> +			if (kip->slot_used[i] == SLOT_DIRTY &&
> +			    collect_one_slot(kip, i))
> +				break;
> +		}
> +	}
> +	c->nr_garbage = 0;
> +	return 0;
> +}
> +
> +kprobe_opcode_t  *__ppc_get_optinsn_slot(struct kprobe_insn_cache *c)
> +{
> +	struct kprobe_ppc_insn_page *kip;
> +	kprobe_opcode_t *slot = NULL;
> +
> +	mutex_lock(&c->mutex);
> +	list_for_each_entry(kip, &c->pages, list) {
> +		if (kip->nused < ppc_slots_per_page(c)) {
> +			int i;
> +
> +			for (i = 0; i < ppc_slots_per_page(c); i++) {
> +				if (kip->slot_used[i] == SLOT_CLEAN) {
> +					kip->slot_used[i] = SLOT_USED;
> +					kip->nused++;
> +					slot = kip->insns + (i * c->insn_size);
> +					goto out;
> +				}
> +			}
> +			/* kip->nused reached max value. */
> +			kip->nused = ppc_slots_per_page(c);
> +			WARN_ON(1);
> +		}
> +		if (!list_empty(&c->pages)) {
> +			pr_info("No more slots to allocate\n");
> +			return NULL;
> +		}

Ah, at this point this is always true!
what I meant was, checking it right after this loop (list_for_each_entry)
we should do that.

BTW, why wouldn't you reuse current insn_slot code?
Maybe you just need following function to allocate the
scratch pad instead of cloning code (or above code).

----
static bool __ppc_insn_page_used;
/*
 * Allocate from the reserved area so as to
 * ensure the range will be within +/-32MB
 */
static void *__ppc_alloc_insn_page(void)
{
	__ppc_insn_page_used = true;
	return optinsn_slot
}

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

> +static struct kprobe_insn_cache kprobe_ppc_optinsn_slots = {
> +	.mutex = __MUTEX_INITIALIZER(kprobe_ppc_optinsn_slots.mutex),
	.alloc = __ppc_alloc_insn_page,
	.free = __ppc_free_insn_page,
> +	.pages = LIST_HEAD_INIT(kprobe_ppc_optinsn_slots.pages),
> +	/* .insn_size is initialized later */
> +	.nr_garbage = 0,
> +};
----- 

This can simplify the code.

> +	}
> +	kip = kmalloc(PPC_KPROBE_INSN_PAGE_SIZE(ppc_slots_per_page(c)),
> +		      GFP_KERNEL);
> +	if (!kip)
> +		goto out;
> +	/*
> +	 * Allocate from the reserved area so as to
> +	 * ensure the range will be within +/-32MB
> +	 */
> +	kip->insns = &optinsn_slot;
> +	if (!kip->insns) {
> +		kfree(kip);
> +		goto out;
> +	}
> +	INIT_LIST_HEAD(&kip->list);
> +	memset(kip->slot_used, SLOT_CLEAN, ppc_slots_per_page(c));
> +	kip->slot_used[0] = SLOT_USED;
> +	kip->nused = 1;
> +	kip->ngarbage = 0;
> +	kip->cache = c;
> +	list_add(&kip->list, &c->pages);
> +	slot = kip->insns;
> +out:
> +	mutex_unlock(&c->mutex);
> +	return slot;
> +}
> +
> +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 = __ppc_get_optinsn_slot(&kprobe_ppc_optinsn_slots);
> +	else
> +		pr_info("Kprobe can not be optimized\n");
> +	return slot;
> +}
> +
> +void __ppc_free_optinsn_slot(struct kprobe_insn_cache *c,
> +			     kprobe_opcode_t *slot, int dirty)
> +{
> +	struct kprobe_ppc_insn_page *kip;
> +
> +	mutex_lock(&c->mutex);
> +
> +	list_for_each_entry(kip, &c->pages, list) {
> +		long idx = ((long)slot - (long)kip->insns) /
> +				(c->insn_size * sizeof(kprobe_opcode_t));
> +		if (idx >= 0 && idx < ppc_slots_per_page(c)) {
> +			WARN_ON(kip->slot_used[idx] != SLOT_USED);
> +			if (dirty) {
> +				kip->slot_used[idx] = SLOT_DIRTY;
> +				kip->ngarbage++;
> +				if (++c->nr_garbage > ppc_slots_per_page(c))
> +					collect_garbage_slots(c);
> +			} else
> +				collect_one_slot(kip, idx);
> +			goto out;
> +		}
> +	}
> +	/* Could not free this slot. */
> +	WARN_ON(1);
> +out:
> +	mutex_unlock(&c->mutex);
> +}
> +
> +static void ppc_free_optinsn_slot(struct optimized_kprobe *op)
> +{
> +	if (!op->optinsn.insn)
> +		return;
> +	if (is_kernel_addr((unsigned long)op->kp.addr))
> +		__ppc_free_optinsn_slot(&kprobe_ppc_optinsn_slots,
> +					op->optinsn.insn, 0);
> +}
> +
> +static void
> +__arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
> +{
> +	if (op->optinsn.insn) {
> +		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 = current_pt_regs();
> +	instr = *(p->ainsn.insn);
> +
> +	/* Ensure the instruction can be emulated*/
> +	r = emulate_step(regs, instr);
> +	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;
> +
> +	branch = create_branch((unsigned int *)buff + TMPL_RET_IDX,
> +			       (unsigned long)ret, 0);
> +	buff[TMPL_RET_IDX] = branch;
> +}
> +
> +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(struct optimized_kprobe *op,
> +			      kprobe_opcode_t *addr, kprobe_opcode_t *addr2)
> +{
> +	u32 instr1, instr2, instr3, instr4, instr5;
> +	unsigned long val;
> +
> +	val = op;
> +
> +	/*
> +	 * 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;
> +	*addr2++ = instr1;
> +
> +	/* ori r3,r3,(op)@higher */
> +	instr2 = 0x60000000 | 0x30000 | 0x600000 | ((val >> 32) & 0xffff);
> +	*addr++ = instr2;
> +	*addr2++ = instr2;
> +
> +	/* rldicr r3,r3,32,31 */
> +	instr3 = 0x78000004 | 0x30000 | 0x600000 | ((32 & 0x1f) << 11);
> +	instr3 = instr3 | ((31 & 0x1f) << 6) | ((32 & 0x20) >> 4);
> +	*addr++ = instr3;
> +	*addr2++ = instr3;
> +
> +	/* oris r3,r3,(op)@h */
> +	instr4 = 0x64000000 |  0x30000 | 0x600000 | ((val >> 16) & 0xffff);
> +	*addr++ = instr4;
> +	*addr2++ = instr4;
> +
> +	/* ori r3,r3,(op)@l */
> +	instr5 =  0x60000000 | 0x30000 | 0x600000 | (val & 0xffff);
> +	*addr = instr5;
> +	*addr2 = 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;

There still be a new line...

> +	if (rel_chk < -0x2000000 || rel_chk > 0x1fffffc || rel_chk & 0x3) {
> +		ppc_free_optinsn_slot(op);
> +		return -ERANGE;
> +	}
> +	/*
> +	 * For the time being assume that the return address is NIP+4.
> +	 * TODO : check the return address is also within 32MB range for
> +	 * cases where NIP is not NIP+4.ie the NIP is decided after emulation.
> +	 */
> +	ret_chk = (long)(buff + TMPL_RET_IDX) - (unsigned long)(p->addr) + 4;
> +	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(op, buff + TMPL_OP1_IDX, 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;
> +	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
> +	*/

This comment should also be indented.

> +		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
> 

Thanks!

-- 
Masami Hiramatsu <[email-masked]>