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

[Palmer Dabbelt]

On Wed, 12 May 2021 07:58:19 PDT (-0700), jszhang3@xxxxxxxxxxxxxxxx wrote:
> 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.

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

> 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;
> >  }