Date:   Wed, 14 Dec 2022 16:28:47 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 2/4] LoongArch: Add kprobe support

Hi,

On Fri,  9 Dec 2022 16:52:59 +0800
Tiezhu Yang <yangtiezhu@...ngson.cn> 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    |  15 ++
>  arch/loongarch/include/asm/kprobes.h |  59 ++++++
>  arch/loongarch/kernel/Makefile       |   2 +
>  arch/loongarch/kernel/kprobes.c      | 340 +++++++++++++++++++++++++++++++++++
>  arch/loongarch/kernel/traps.c        |  13 +-
>  arch/loongarch/mm/fault.c            |   3 +
>  7 files changed, 429 insertions(+), 4 deletions(-)
>  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 16bf1b6..f6fc156 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -102,6 +102,7 @@ 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 e25fd54..a7c85df 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -24,6 +24,10 @@
>  
>  #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,
> @@ -180,6 +184,11 @@ 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;
> @@ -265,6 +274,7 @@ 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;
> @@ -335,6 +345,11 @@ static inline bool is_branch_ins(union loongarch_instruction *ip)
>  		ip->reg1i21_format.opcode <= bgeu_op;
>  }
>  
> +static inline bool is_break_ins(union loongarch_instruction *ip)
> +{
> +	return ip->reg0i15_format.opcode == break_op;
> +}
> +
>  static inline bool is_ra_save_ins(union loongarch_instruction *ip)
>  {
>  	/* st.d $ra, $sp, offset */
> diff --git a/arch/loongarch/include/asm/kprobes.h b/arch/loongarch/include/asm/kprobes.h
> new file mode 100644
> index 0000000..d3903f3
> --- /dev/null
> +++ b/arch/loongarch/include/asm/kprobes.h
> @@ -0,0 +1,59 @@
> +/* 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);
> +bool kprobe_breakpoint_handler(struct pt_regs *regs);
> +bool kprobe_singlestep_handler(struct pt_regs *regs);
> +
> +#else /* !CONFIG_KPROBES */
> +
> +static inline bool kprobe_breakpoint_handler(struct pt_regs *regs) { return 0; }
> +static inline bool kprobe_singlestep_handler(struct pt_regs *regs) { return 0; }

bool should return true or false.

> +
> +#endif /* CONFIG_KPROBES */
> +#endif /* __ASM_LOONGARCH_KPROBES_H */
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index fcaa024..6fe4a4e 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -47,4 +47,6 @@ 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..546a3c3
> --- /dev/null
> +++ b/arch/loongarch/kernel/kprobes.c
> @@ -0,0 +1,340 @@
> +// 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_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 and sc instructions are not supported\n");
> +		return true;
> +	}
> +
> +	switch (insn.reg1i21_format.opcode) {
> +	case bceqz_op:
> +		pr_notice("kprobe: bceqz and bcnez instructions are not supported\n");
> +		return true;
> +	}
> +
> +	return false;
> +}
> +NOKPROBE_SYMBOL(insns_not_supported);
> +
> +int arch_prepare_kprobe(struct kprobe *p)
> +{
> +	union loongarch_instruction insn;
> +
> +	insn = p->addr[0];
> +	if (insns_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_not_simulated(struct kprobe *p, struct pt_regs *regs)

I recommend this as "insn_simulate()" and return false if it is NOT
simulated, since this actually simulates the instruction, 

> +{
> +	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_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;
> +	}
> +
> +	regs->csr_prmd &= ~CSR_PRMD_PIE;
> +
> +	if (p->ainsn.insn->word == breakpoint_insn.word) {

Would you mean there is already another kprobe on the same address
and it is copied? The kprobe arch-independent code already checked
that and if you see this when registering new one in the arch
code, it should be rejected.

> +		regs->csr_prmd |= kcb->kprobe_saved_irq;
> +		preempt_enable_no_resched();
> +		return;
> +	}
> +
> +	if (insns_not_simulated(p, regs)) {

if (!insn_simulate(p, regs)) {
	/* fall back to normal single stepping */

> +		kcb->kprobe_status = KPROBE_HIT_SS;

No, if reentered == true, it should be KPROBE_REENTER during the
single stepping.

> +		regs->csr_era = (unsigned long)&p->ainsn.insn[0];
> +	} else {
> +		kcb->kprobe_status = KPROBE_HIT_SSDONE;

You also missed reentering case. If the kprobes hits in another kprobe
handler, it must be in KPROBE_REENTER state and do not call any user
handler.

> +		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);
> +
> +bool kprobe_breakpoint_handler(struct pt_regs *regs)
> +{
> +	struct kprobe_ctlblk *kcb;
> +	struct kprobe *p, *cur_kprobe;
> +	kprobe_opcode_t *addr = (kprobe_opcode_t *)regs->csr_era;
> +
> +	/*
> +	 * We don't want to be preempted for the entire
> +	 * duration of kprobe processing.
> +	 */
> +	preempt_disable();
> +	kcb = get_kprobe_ctlblk();
> +	cur_kprobe = kprobe_running();
> +
> +	p = get_kprobe(addr);
> +	if (p) {
> +		if (cur_kprobe) {
> +			if (reenter_kprobe(p, regs, kcb))
> +				return true;

 even if reenter_kprobe() doesn't return true, this function
eventually 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;

		^Here.

> +	}
> +
> +	if (!is_break_ins(addr)) {
> +		/*
> +		 * 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 true;
> +	}
> +
> +	preempt_enable_no_resched();
> +	return false;
> +}
> +NOKPROBE_SYMBOL(kprobe_breakpoint_handler);
> +
> +bool kprobe_singlestep_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 */
> +	if (cur->post_handler) {
> +		kcb->kprobe_status = KPROBE_HIT_SSDONE;
> +		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(kprobe_singlestep_handler);
> +
> +bool kprobe_fault_handler(struct pt_regs *regs, int trapnr)
> +{
> +	struct kprobe *cur = kprobe_running();
> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> +
> +	switch (kcb->kprobe_status) {
> +	case KPROBE_HIT_SS:
> +	case KPROBE_REENTER:
> +		/*
> +		 * We are here because the instruction being single
> +		 * stepped caused a page fault. We reset the current
> +		 * kprobe and the ip points back to the probe address
> +		 * and allow the page fault handler to continue as a
> +		 * normal page fault.
> +		 */
> +		regs->csr_era = (unsigned long) cur->addr;
> +		BUG_ON(!instruction_pointer(regs));
> +
> +		if (kcb->kprobe_status == KPROBE_REENTER) {
> +			restore_previous_kprobe(kcb);
> +		} else {
> +			regs->csr_prmd |= kcb->kprobe_saved_irq;
> +			reset_current_kprobe();
> +		}
> +		preempt_enable_no_resched();
> +		break;
> +	case KPROBE_HIT_ACTIVE:
> +	case KPROBE_HIT_SSDONE:

Recently, I removed these cases because this page fault will be finally
handled by the generic pagefault handler.

Thank you,

> +		/*
> +		 * In case the user-specified fault handler returned
> +		 * zero, try to fix up.
> +		 */
> +		if (fixup_exception(regs))
> +			return true;
> +
> +		/*
> +		 * If fixup_exception() could not handle it,
> +		 * let do_page_fault() fix it.
> +		 */
> +		break;
> +	default:
> +		break;
> +	}
> +	return false;
> +}
> +NOKPROBE_SYMBOL(kprobe_fault_handler);
> +
> +/*
> + * 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/kernel/traps.c b/arch/loongarch/kernel/traps.c
> index a19bb32..4d9f775 100644
> --- a/arch/loongarch/kernel/traps.c
> +++ b/arch/loongarch/kernel/traps.c
> @@ -448,14 +448,12 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
>  	 */
>  	switch (bcode) {
>  	case BRK_KPROBE_BP:
> -		if (notify_die(DIE_BREAK, "Kprobe", regs, bcode,
> -			       current->thread.trap_nr, SIGTRAP) == NOTIFY_STOP)
> +		if (kprobe_breakpoint_handler(regs))
>  			goto out;
>  		else
>  			break;
>  	case BRK_KPROBE_SSTEPBP:
> -		if (notify_die(DIE_SSTEPBP, "Kprobe_SingleStep", regs, bcode,
> -			       current->thread.trap_nr, SIGTRAP) == NOTIFY_STOP)
> +		if (kprobe_singlestep_handler(regs))
>  			goto out;
>  		else
>  			break;
> @@ -479,6 +477,13 @@ asmlinkage void noinstr do_bp(struct pt_regs *regs)
>  			break;
>  	}
>  
> +	if (bcode == BRK_KPROBE_BP) {
> +		if (__get_inst(&opcode, (u32 *)era, user))
> +			goto out_sigsegv;
> +
> +		bcode = (opcode & 0x7fff);
> +	}
> +
>  	switch (bcode) {
>  	case BRK_BUG:
>  		bug_handler(regs);
> diff --git a/arch/loongarch/mm/fault.c b/arch/loongarch/mm/fault.c
> index 1ccd536..449087b 100644
> --- a/arch/loongarch/mm/fault.c
> +++ b/arch/loongarch/mm/fault.c
> @@ -135,6 +135,9 @@ static void __kprobes __do_page_fault(struct pt_regs *regs,
>  	struct vm_area_struct *vma = NULL;
>  	vm_fault_t fault;
>  
> +	if (kprobe_page_fault(regs, current->thread.trap_nr))
> +		return;
> +
>  	/*
>  	 * We fault-in kernel-space virtual memory on-demand. The
>  	 * 'reference' page table is init_mm.pgd.
> -- 
> 2.1.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>

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