[PATCH] arm64: kprobes: Remove redundant kprobe_step_ctx

[Jean-Philippe Brucker]

On Fri, Oct 30, 2020 at 10:13:08AM +0900, Masami Hiramatsu wrote:
> The kprobe_step_ctx (kcb->ss_ctx) has ss_pending and match_addr, but
> those are redundant because those can be replaced by KPROBE_HIT_SS and
> &cur_kprobe->ainsn.api.insn[1] respectively.
> To simplify the code, remove the kprobe_step_ctx.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat at kernel.org>

Reviewed-by: Jean-Philippe Brucker <jean-philippe at linaro.org>

> ---
>  arch/arm64/include/asm/kprobes.h   |    7 -----
>  arch/arm64/kernel/probes/kprobes.c |   53 ++++++++----------------------------
>  2 files changed, 12 insertions(+), 48 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kprobes.h b/arch/arm64/include/asm/kprobes.h
> index 8699ce30f587..5d38ff4a4806 100644
> --- a/arch/arm64/include/asm/kprobes.h
> +++ b/arch/arm64/include/asm/kprobes.h
> @@ -28,18 +28,11 @@ 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_irqflag;
>  	struct prev_kprobe prev_kprobe;
> -	struct kprobe_step_ctx ss_ctx;
>  };
>  
>  void arch_remove_kprobe(struct kprobe *);
> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
> index ec1446ceacc9..3c74fc9e2acf 100644
> --- a/arch/arm64/kernel/probes/kprobes.c
> +++ b/arch/arm64/kernel/probes/kprobes.c
> @@ -34,7 +34,7 @@ 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 int __kprobes patch_text(kprobe_opcode_t *addr, u32 opc1, u32 opc2)
>  {
> @@ -81,7 +81,7 @@ static void __kprobes arch_simulate_insn(struct kprobe *p, struct pt_regs *regs)
>  		p->ainsn.api.handler((u32)p->opcode, (long)p->addr, regs);
>  
>  	/* single step simulated, now go for post processing */
> -	post_kprobe_handler(kcb, regs);
> +	post_kprobe_handler(p, kcb, regs);
>  }
>  
>  int __kprobes arch_prepare_kprobe(struct kprobe *p)
> @@ -184,19 +184,6 @@ static void __kprobes kprobes_restore_local_irqflag(struct kprobe_ctlblk *kcb,
>  	regs->pstate |= kcb->saved_irqflag;
>  }
>  
> -static void __kprobes
> -set_ss_context(struct kprobe_ctlblk *kcb, unsigned long addr)
> -{
> -	kcb->ss_ctx.ss_pending = true;
> -	kcb->ss_ctx.match_addr = addr + sizeof(kprobe_opcode_t);
> -}
> -
> -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)
> @@ -216,7 +203,6 @@ static void __kprobes setup_singlestep(struct kprobe *p,
>  		/* prepare for single stepping */
>  		slot = (unsigned long)p->ainsn.api.insn;
>  
> -		set_ss_context(kcb, slot);	/* mark pending ss */
>  		kprobes_save_local_irqflag(kcb, regs);
>  		instruction_pointer_set(regs, slot);
>  	} else {
> @@ -250,13 +236,8 @@ 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)
>  		instruction_pointer_set(regs, cur->ainsn.api.restore);
> @@ -371,33 +352,23 @@ static void __kprobes kprobe_handler(struct pt_regs *regs)
>  	 */
>  }
>  
> -static int __kprobes
> -kprobe_ss_hit(struct kprobe_ctlblk *kcb, unsigned long addr)
> -{
> -	if ((kcb->ss_ctx.ss_pending)
> -	    && (kcb->ss_ctx.match_addr == addr)) {
> -		clear_ss_context(kcb);	/* clear pending ss */
> -		return DBG_HOOK_HANDLED;
> -	}
> -	/* not ours, kprobes should ignore it */
> -	return DBG_HOOK_ERROR;
> -}
> -
>  static int __kprobes
>  kprobe_breakpoint_ss_handler(struct pt_regs *regs, unsigned int esr)
>  {
>  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> -	int retval;
> -
> -	/* return error if this is not our step */
> -	retval = kprobe_ss_hit(kcb, instruction_pointer(regs));
> +	unsigned long addr = instruction_pointer(regs);
> +	struct kprobe *cur = kprobe_running();
>  
> -	if (retval == DBG_HOOK_HANDLED) {
> +	if (cur && (kcb->kprobe_status == KPROBE_HIT_SS)
> +	    && ((unsigned long)&cur->ainsn.api.insn[1] == addr)) {
>  		kprobes_restore_local_irqflag(kcb, regs);
> -		post_kprobe_handler(kcb, regs);
> +		post_kprobe_handler(cur, kcb, regs);
> +
> +		return DBG_HOOK_HANDLED;
>  	}
>  
> -	return retval;
> +	/* not ours, kprobes should ignore it */
> +	return DBG_HOOK_ERROR;
>  }
>  
>  static struct break_hook kprobes_break_ss_hook = {
>