linux-kernel - Re: [PATCH] riscv: kprobes: Remove redundant kprobe_step

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Message-ID: <mhng-458b641d-fe97-4d92-8a6a-e43240aeb0c3@palmerdabbelt-glaptop>
Date:   Sat, 29 May 2021 11:40:37 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     jszhang3@...l.ustc.edu.cn
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        mhiramat@...nel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject:     Re: [PATCH] riscv: kprobes: Remove redundant kprobe_step_ctx

On Wed, 12 May 2021 07:58:19 PDT (-0700), jszhang3@...l.ustc.edu.cn wrote:
> On Mon, 19 Apr 2021 00:29:19 +0800
> Jisheng Zhang <jszhang3@...l.ustc.edu.cn> wrote:
>
>> From: Jisheng Zhang <jszhang@...nel.org>
>>
>> Inspired by commit ba090f9cafd5 ("arm64: kprobes: Remove redundant
>> kprobe_step_ctx"), the ss_pending and match_addr of kprobe_step_ctx
>> are redundant because those can be replaced by KPROBE_HIT_SS and
>> &cur_kprobe->ainsn.api.insn[0] + GET_INSN_LENGTH(cur->opcode)
>> respectively.
>>
>> Remove the kprobe_step_ctx to simplify the code.
>
> Hi all,
>
> This patch can still be applied to 5.13-rc1, could you please review? Let me
> know if a rebase on 5.13-rc1 is needed.

Sorry, I missed this one.  This is on for-next.

>
> Thanks
>
>>
>> Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
>> ---
>>  arch/riscv/include/asm/kprobes.h   |  7 ------
>>  arch/riscv/kernel/probes/kprobes.c | 40 +++++++-----------------------
>>  2 files changed, 9 insertions(+), 38 deletions(-)
>>
>> diff --git a/arch/riscv/include/asm/kprobes.h b/arch/riscv/include/asm/kprobes.h
>> index 4647d38018f6..9ea9b5ec3113 100644
>> --- a/arch/riscv/include/asm/kprobes.h
>> +++ b/arch/riscv/include/asm/kprobes.h
>> @@ -29,18 +29,11 @@ struct prev_kprobe {
>>  	unsigned int status;
>>  };
>>
>> -/* Single step context for kprobe */
>> -struct kprobe_step_ctx {
>> -	unsigned long ss_pending;
>> -	unsigned long match_addr;
>> -};
>> -
>>  /* per-cpu kprobe control block */
>>  struct kprobe_ctlblk {
>>  	unsigned int kprobe_status;
>>  	unsigned long saved_status;
>>  	struct prev_kprobe prev_kprobe;
>> -	struct kprobe_step_ctx ss_ctx;
>>  };
>>
>>  void arch_remove_kprobe(struct kprobe *p);
>> diff --git a/arch/riscv/kernel/probes/kprobes.c b/arch/riscv/kernel/probes/kprobes.c
>> index 8c1f7a30aeed..4c1ad5536748 100644
>> --- a/arch/riscv/kernel/probes/kprobes.c
>> +++ b/arch/riscv/kernel/probes/kprobes.c
>> @@ -17,7 +17,7 @@ DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
>>  DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>>
>>  static void __kprobes
>> -post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);
>> +post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>>
>>  static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
>>  {
>> @@ -43,7 +43,7 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
>>  		p->ainsn.api.handler((u32)p->opcode,
>>  					(unsigned long)p->addr, regs);
>>
>> -	post_kprobe_handler(kcb, regs);
>> +	post_kprobe_handler(p, kcb, regs);
>>  }
>>
>>  int __kprobes arch_prepare_kprobe(struct kprobe *p)
>> @@ -149,21 +149,6 @@ static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
>>  	regs->status = kcb->saved_status;
>>  }
>>
>> -static void __kprobes
>> -set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr, struct kprobe *p)
>> -{
>> -	unsigned long offset = GET_INSN_LENGTH(p->opcode);
>> -
>> -	kcb->ss_ctx.ss_pending = true;
>> -	kcb->ss_ctx.match_addr = addr + offset;
>> -}
>> -
>> -static void __kprobes clear_ss_context(struct kprobe_ctlblk *kcb)
>> -{
>> -	kcb->ss_ctx.ss_pending = false;
>> -	kcb->ss_ctx.match_addr = 0;
>> -}
>> -
>>  static void __kprobes setup_singlestep(struct kprobe *p,
>>  				       struct pt_regs *regs,
>>  				       struct kprobe_ctlblk *kcb, int reenter)
>> @@ -182,8 +167,6 @@ static void __kprobes setup_singlestep(struct kprobe *p,
>>  		/* prepare for single stepping */
>>  		slot = (unsigned long)p->ainsn.api.insn;
>>
>> -		set_ss_context(kcb, slot, p);	/* mark pending ss */
>> -
>>  		/* IRQs and single stepping do not mix well. */
>>  		kprobes_save_local_irqflag(kcb, regs);
>>
>> @@ -219,13 +202,8 @@ static int __kprobes reenter_kprobe(struct kprobe *p,
>>  }
>>
>>  static void __kprobes
>> -post_kprobe_handler(struct kprobe_ctlblk *kcb, struct pt_regs *regs)
>> +post_kprobe_handler(struct kprobe *cur, struct kprobe_ctlblk *kcb, struct pt_regs *regs)
>>  {
>> -	struct kprobe *cur = kprobe_running();
>> -
>> -	if (!cur)
>> -		return;
>> -
>>  	/* return addr restore if non-branching insn */
>>  	if (cur->ainsn.api.restore != 0)
>>  		regs->epc = cur->ainsn.api.restore;
>> @@ -355,16 +333,16 @@ bool __kprobes
>>  kprobe_single_step_handler(struct pt_regs *regs)
>>  {
>>  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>> +	unsigned long addr = instruction_pointer(regs);
>> +	struct kprobe *cur = kprobe_running();
>>
>> -	if ((kcb->ss_ctx.ss_pending)
>> -	    && (kcb->ss_ctx.match_addr == instruction_pointer(regs))) {
>> -		clear_ss_context(kcb);	/* clear pending ss */
>> -
>> +	if (cur && (kcb->kprobe_status & (KPROBE_HIT_SS | KPROBE_REENTER)) &&
>> +	    ((unsigned long)&cur->ainsn.api.insn[0] + GET_INSN_LENGTH(cur->opcode) == addr)) {
>>  		kprobes_restore_local_irqflag(kcb, regs);
>> -
>> -		post_kprobe_handler(kcb, regs);
>> +		post_kprobe_handler(cur, kcb, regs);
>>  		return true;
>>  	}
>> +	/* not ours, kprobes should ignore it */
>>  	return false;
>>  }
>>