Date:   Wed, 16 Nov 2022 11:20:22 +0800
From:   Qing Zhang <zhangqing@...ngson.cn>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/4] LoongArch: Add kprobe support

Hi, tiezhu

On 2022/11/16 上午10:36, Tiezhu Yang wrote:
> Kprobes allows you to trap at almost any kernel address and
> execute a callback function, this commit adds kprobe support
> for LoongArch.
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>   arch/loongarch/Kconfig               |   1 +
>   arch/loongarch/include/asm/inst.h    |  10 ++
>   arch/loongarch/include/asm/kprobes.h |  52 ++++++
>   arch/loongarch/kernel/Makefile       |   2 +
>   arch/loongarch/kernel/kprobes.c      | 324 +++++++++++++++++++++++++++++++++++
>   arch/loongarch/mm/fault.c            |   4 +
>   6 files changed, 393 insertions(+)
>   create mode 100644 arch/loongarch/include/asm/kprobes.h
>   create mode 100644 arch/loongarch/kernel/kprobes.c
> 
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index 1943f84..cd71a86 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -95,6 +95,7 @@ config LOONGARCH
>   	select HAVE_IOREMAP_PROT
>   	select HAVE_IRQ_EXIT_ON_IRQ_STACK
>   	select HAVE_IRQ_TIME_ACCOUNTING
> +	select HAVE_KPROBES
>   	select HAVE_MOD_ARCH_SPECIFIC
>   	select HAVE_NMI
>   	select HAVE_PCI
> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> index dea85e7..3e2f870 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -22,6 +22,10 @@
>   
>   #define ADDR_IMM(addr, INSN)	((addr & ADDR_IMMMASK_##INSN) >> ADDR_IMMSHIFT_##INSN)
>   
> +enum reg0i15_op {
> +	break_op	= 0x54,
> +};
> +
>   enum reg0i26_op {
>   	b_op		= 0x14,
>   	bl_op		= 0x15,
> @@ -178,6 +182,11 @@ enum reg3sa2_op {
>   	alsld_op	= 0x16,
>   };
>   
> +struct reg0i15_format {
> +	unsigned int immediate : 15;
> +	unsigned int opcode : 17;
> +};
> +
>   struct reg0i26_format {
>   	unsigned int immediate_h : 10;
>   	unsigned int immediate_l : 16;
> @@ -263,6 +272,7 @@ struct reg3sa2_format {
>   
>   union loongarch_instruction {
>   	unsigned int word;
> +	struct reg0i15_format	reg0i15_format;
>   	struct reg0i26_format	reg0i26_format;
>   	struct reg1i20_format	reg1i20_format;
>   	struct reg1i21_format	reg1i21_format;
> diff --git a/arch/loongarch/include/asm/kprobes.h b/arch/loongarch/include/asm/kprobes.h
> new file mode 100644
> index 0000000..4579885
> --- /dev/null
> +++ b/arch/loongarch/include/asm/kprobes.h
> @@ -0,0 +1,52 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef __ASM_LOONGARCH_KPROBES_H
> +#define __ASM_LOONGARCH_KPROBES_H
> +
> +#include <asm-generic/kprobes.h>
> +#include <asm/cacheflush.h>
> +
> +#ifdef CONFIG_KPROBES
> +
> +#include <asm/inst.h>
> +
> +#define __ARCH_WANT_KPROBES_INSN_SLOT
> +#define MAX_INSN_SIZE			2
> +
> +#define flush_insn_slot(p)						\
> +do {									\
> +	if (p->addr)							\
> +		flush_icache_range((unsigned long)p->addr,		\
> +			   (unsigned long)p->addr +			\
> +			   (MAX_INSN_SIZE * sizeof(kprobe_opcode_t)));	\
> +} while (0)
> +
> +#define kretprobe_blacklist_size	0
> +
> +typedef union loongarch_instruction kprobe_opcode_t;
> +
> +/* Architecture specific copy of original instruction */
> +struct arch_specific_insn {
> +	/* copy of the original instruction */
> +	kprobe_opcode_t *insn;
> +};
> +
> +struct prev_kprobe {
> +	struct kprobe *kp;
> +	unsigned long status;
> +	unsigned long saved_irq;
> +	unsigned long saved_era;
> +};
> +
> +/* per-cpu kprobe control block */
> +struct kprobe_ctlblk {
> +	unsigned long kprobe_status;
> +	unsigned long kprobe_saved_irq;
> +	unsigned long kprobe_saved_era;
> +	struct prev_kprobe prev_kprobe;
> +};
> +
> +void arch_remove_kprobe(struct kprobe *p);
> +bool kprobe_fault_handler(struct pt_regs *regs, int trapnr);
> +
> +#endif /* CONFIG_KPROBES */
> +#endif /* __ASM_LOONGARCH_KPROBES_H */
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index 8674453..ac77eb7 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -34,4 +34,6 @@ obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
>   
>   obj-$(CONFIG_PERF_EVENTS)	+= perf_event.o perf_regs.o
>   
> +obj-$(CONFIG_KPROBES)		+= kprobes.o
> +
>   CPPFLAGS_vmlinux.lds		:= $(KBUILD_CFLAGS)
> diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/kprobes.c
> new file mode 100644
> index 0000000..a6858f9
> --- /dev/null
> +++ b/arch/loongarch/kernel/kprobes.c
> @@ -0,0 +1,324 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +#include <linux/kprobes.h>
> +#include <linux/kdebug.h>
> +#include <linux/preempt.h>
> +#include <asm/break.h>
> +
> +static const union loongarch_instruction breakpoint_insn = {
> +	.reg0i15_format = {
> +		.opcode = break_op,
> +		.immediate = BRK_KPROBE_BP,
> +	}
> +};
> +
> +static const union loongarch_instruction singlestep_insn = {
> +	.reg0i15_format = {
> +		.opcode = break_op,
> +		.immediate = BRK_KPROBE_SSTEPBP,
> +	}
> +};
> +
> +DEFINE_PER_CPU(struct kprobe *, current_kprobe);
> +DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
> +
> +static bool insns_are_not_supported(union loongarch_instruction insn)
> +{
> +	switch (insn.reg2i14_format.opcode) {
> +	case llw_op:
> +	case lld_op:
> +	case scw_op:
> +	case scd_op:
> +		pr_notice("kprobe: ll or sc instructions are not supported\n");
> +		return true;
> +	}
> +
> +	switch (insn.reg1i21_format.opcode) {
> +	case bceqz_op:
> +		pr_notice("kprobe: bceqz or bcnez instructions are not supported\n");
> +		return true;
> +	}
> +
> +	return false;
> +}
> +NOKPROBE_SYMBOL(insns_are_not_supported);
> +
> +int arch_prepare_kprobe(struct kprobe *p)
> +{
> +	union loongarch_instruction insn;
> +
> +	insn = p->addr[0];
> +	if (insns_are_not_supported(insn))
> +		return -EINVAL;
> +
> +	p->ainsn.insn = get_insn_slot();
> +	if (!p->ainsn.insn)
> +		return -ENOMEM;
> +
> +	p->ainsn.insn[0] = *p->addr;
> +	p->ainsn.insn[1] = singlestep_insn;
> +
> +	p->opcode = *p->addr;
> +
> +	return 0;
> +}
> +NOKPROBE_SYMBOL(arch_prepare_kprobe);
> +
> +/* Install breakpoint in text */
> +void arch_arm_kprobe(struct kprobe *p)
> +{
> +	*p->addr = breakpoint_insn;
> +	flush_insn_slot(p);
> +}
> +NOKPROBE_SYMBOL(arch_arm_kprobe);
> +
> +/* Remove breakpoint from text */
> +void arch_disarm_kprobe(struct kprobe *p)
> +{
> +	*p->addr = p->opcode;
> +	flush_insn_slot(p);
> +}
> +NOKPROBE_SYMBOL(arch_disarm_kprobe);
> +
> +void arch_remove_kprobe(struct kprobe *p)
> +{
> +	if (p->ainsn.insn) {
> +		free_insn_slot(p->ainsn.insn, 0);
> +		p->ainsn.insn = NULL;
> +	}
> +}
> +NOKPROBE_SYMBOL(arch_remove_kprobe);
> +
> +static void save_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> +	kcb->prev_kprobe.kp = kprobe_running();
> +	kcb->prev_kprobe.status = kcb->kprobe_status;
> +	kcb->prev_kprobe.saved_irq = kcb->kprobe_saved_irq;
> +	kcb->prev_kprobe.saved_era = kcb->kprobe_saved_era;
> +}
> +NOKPROBE_SYMBOL(save_previous_kprobe);
> +
> +static void restore_previous_kprobe(struct kprobe_ctlblk *kcb)
> +{
> +	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
> +	kcb->kprobe_status = kcb->prev_kprobe.status;
> +	kcb->kprobe_saved_irq = kcb->prev_kprobe.saved_irq;
> +	kcb->kprobe_saved_era = kcb->prev_kprobe.saved_era;
> +}
> +NOKPROBE_SYMBOL(restore_previous_kprobe);
> +
> +static void set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
> +			       struct kprobe_ctlblk *kcb)
> +{
> +	__this_cpu_write(current_kprobe, p);
> +	kcb->kprobe_saved_irq = regs->csr_prmd & CSR_PRMD_PIE;
> +	kcb->kprobe_saved_era = regs->csr_era;
> +}
> +NOKPROBE_SYMBOL(set_current_kprobe);
> +
> +static bool insns_are_not_simulated(struct kprobe *p, struct pt_regs *regs)
> +{
> +	if (is_branch_ins(&p->opcode)) {
> +		simu_branch(regs, p->opcode);
> +		return false;
> +	} else if (is_pc_ins(&p->opcode)) {
> +		simu_pc(regs, p->opcode);
> +		return false;
> +	} else {
> +		return true;
> +	}
> +}
> +NOKPROBE_SYMBOL(insns_are_not_simulated);
> +
> +static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
> +			     struct kprobe_ctlblk *kcb, int reenter)
> +{
> +	if (reenter) {
> +		save_previous_kprobe(kcb);
> +		set_current_kprobe(p, regs, kcb);
> +		kcb->kprobe_status = KPROBE_REENTER;
> +	} else {
> +		kcb->kprobe_status = KPROBE_HIT_SS;
> +	}
> +
> +	if (p->ainsn.insn->word == breakpoint_insn.word) {
> +		regs->csr_prmd &= ~CSR_PRMD_PIE;
> +		regs->csr_prmd |= kcb->kprobe_saved_irq;
> +		preempt_enable_no_resched();
> +		return;
> +	}
> +
> +	regs->csr_prmd &= ~CSR_PRMD_PIE;
> +
> +	if (insns_are_not_simulated(p, regs)) {
> +		kcb->kprobe_status = KPROBE_HIT_SS;
> +		regs->csr_era = (unsigned long)&p->ainsn.insn[0];
> +	} else {
> +		kcb->kprobe_status = KPROBE_HIT_SSDONE;
> +		if (p->post_handler)
> +			p->post_handler(p, regs, 0);
> +		reset_current_kprobe();
> +		preempt_enable_no_resched();
> +	}
> +}
> +NOKPROBE_SYMBOL(setup_singlestep);
> +
> +static bool reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
> +			  struct kprobe_ctlblk *kcb)
> +{
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SSDONE:
> +	case KPROBE_HIT_ACTIVE:
> +		kprobes_inc_nmissed_count(p);
> +		setup_singlestep(p, regs, kcb, 1);
> +		break;
> +	case KPROBE_HIT_SS:
> +	case KPROBE_REENTER:
> +		pr_warn("Failed to recover from reentered kprobes.\n");
> +		dump_kprobe(p);
> +		BUG();
> +		break;
> +	default:
> +		WARN_ON(1);
> +		return false;
> +	}
> +
> +	return true;
> +}
> +NOKPROBE_SYMBOL(reenter_kprobe);
> +
> +static bool kprobe_handler(struct pt_regs *regs)
> +{
> +	struct kprobe *p, *cur_kprobe;
> +	struct kprobe_ctlblk *kcb;
> +	unsigned long addr = instruction_pointer(regs);
> +
> +	preempt_disable();
> +	kcb = get_kprobe_ctlblk();
> +	cur_kprobe = kprobe_running();
> +
> +	p = get_kprobe((kprobe_opcode_t *) addr);
> +	if (p) {
> +		if (cur_kprobe) {
> +			if (reenter_kprobe(p, regs, kcb))
> +				return true;
> +		} else {
> +			/* Probe hit */
> +			set_current_kprobe(p, regs, kcb);
> +			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> +
> +			/*
> +			 * If we have no pre-handler or it returned 0, we
> +			 * continue with normal processing.  If we have a
> +			 * pre-handler and it returned non-zero, it will
> +			 * modify the execution path and no need to single
> +			 * stepping. Let's just reset current kprobe and exit.
> +			 *
> +			 * pre_handler can hit a breakpoint and can step thru
> +			 * before return.
> +			 */
> +			if (!p->pre_handler || !p->pre_handler(p, regs)) {
> +				setup_singlestep(p, regs, kcb, 0);
> +			} else {
> +				reset_current_kprobe();
> +				preempt_enable_no_resched();
> +			}
> +		}
> +		return true;
> +	}
> +
> +	/*
> +	 * The breakpoint instruction was removed right
> +	 * after we hit it.  Another cpu has removed
> +	 * either a probepoint or a debugger breakpoint
> +	 * at this address.  In either case, no further
> +	 * handling of this interrupt is appropriate.
> +	 * Return back to original instruction, and continue.
> +	 */
> +	preempt_enable_no_resched();
> +	return false;
> +}
> +NOKPROBE_SYMBOL(kprobe_handler);
> +
> +static bool post_kprobe_handler(struct pt_regs *regs)
> +{
> +	struct kprobe *cur = kprobe_running();
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	if (!cur)
> +		return false;
> +
> +	/* Restore back the original saved kprobes variables and continue */
> +	if (kcb->kprobe_status == KPROBE_REENTER) {
> +		restore_previous_kprobe(kcb);
> +		goto out;
> +	}
> +
> +	/* Call post handler */
> +	kcb->kprobe_status = KPROBE_HIT_SSDONE;
> +	if (cur->post_handler)
> +		cur->post_handler(cur, regs, 0);
> +
> +	regs->csr_era = kcb->kprobe_saved_era + LOONGARCH_INSN_SIZE;
> +	regs->csr_prmd |= kcb->kprobe_saved_irq;
> +
> +	reset_current_kprobe();
> +out:
> +	preempt_enable_no_resched();
> +
> +	return true;
> +}
> +NOKPROBE_SYMBOL(post_kprobe_handler);
> +
> +bool kprobe_fault_handler(struct pt_regs *regs, int trapnr)
> +{
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	if (kcb->kprobe_status & KPROBE_HIT_SS) {
> +		regs->csr_era = kcb->kprobe_saved_era + LOONGARCH_INSN_SIZE;
> +		regs->csr_prmd |= kcb->kprobe_saved_irq;
> +
> +		reset_current_kprobe();
> +		preempt_enable_no_resched();
> +	}
> +
> +	return false;
> +}
> +NOKPROBE_SYMBOL(kprobe_fault_handler);
> +
> +int kprobe_exceptions_notify(struct notifier_block *self,
> +			     unsigned long val, void *data)
> +{
We should delete kprobe_exceptions_notify,
Call kprobe_handler directly inside the do_bp function, just like any 
other mainstream architecture handler that simulates breakpoints.
I'm doing this with the hardware breakpoint framework, and I hope the 
software breakpoints will do the same.

Thanks
-Qing
> +	struct die_args *args = (struct die_args *)data;
> +	int ret = NOTIFY_DONE;
> +
> +	switch (val) {
> +	case DIE_BREAK:
> +		if (kprobe_handler(args->regs))
> +			ret = NOTIFY_STOP;
> +		break;
> +	case DIE_SSTEPBP:
> +		if (post_kprobe_handler(args->regs))
> +			ret = NOTIFY_STOP;
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	return ret;
> +}
> +NOKPROBE_SYMBOL(kprobe_exceptions_notify);
> +
> +/*
> + * Provide a blacklist of symbols identifying ranges which cannot be kprobed.
> + * This blacklist is exposed to userspace via debugfs (kprobes/blacklist).
> + */
> +int __init arch_populate_kprobe_blacklist(void)
> +{
> +	return kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
> +					 (unsigned long)__irqentry_text_end);
> +}
> +
> +int __init arch_init_kprobes(void)
> +{
> +	return 0;
> +}
> diff --git a/arch/loongarch/mm/fault.c b/arch/loongarch/mm/fault.c
> index 1ccd536..fc9225a 100644
> --- a/arch/loongarch/mm/fault.c
> +++ b/arch/loongarch/mm/fault.c
> @@ -253,12 +253,16 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
>   {
>   	irqentry_state_t state = irqentry_enter(regs);
>   
> +	if (kprobe_page_fault(regs, current->thread.trap_nr))
> +		goto out;
> +
>   	/* Enable interrupt if enabled in parent context */
>   	if (likely(regs->csr_prmd & CSR_PRMD_PIE))
>   		local_irq_enable();
>   
>   	__do_page_fault(regs, write, address);
>   
> +out:
>   	local_irq_disable();
>   
>   	irqentry_exit(regs, state);
> 

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