Re: [PATCH] riscv: kprobes: Remove redundant kprobe_step_ctx

[Jisheng Zhang]

On Mon, 19 Apr 2021 00:29:19 +0800
Jisheng Zhang <jszhang3@xxxxxxxxxxxxxxxx> wrote:

> From: Jisheng Zhang <jszhang@xxxxxxxxxx>
> 
> 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.

Thanks

> 
> Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
> ---
>  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;
>  }
>