linux-kernel - Re: [RFC PATCH 1/1] x86/kprobes: Use int3 instead of debug trap for single-step

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Message-Id: <20210302215124.2614a36fdf084d514dabfc4d@kernel.org>
Date:   Tue, 2 Mar 2021 21:51:24 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>, X86 ML <x86@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH 1/1] x86/kprobes: Use int3 instead of debug trap for
 single-step

On Tue, 2 Mar 2021 09:54:43 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Mar 02, 2021 at 09:41:32AM +0100, Peter Zijlstra wrote:
> 
> > Aside of a few nits:
> 
> something like so..

Thanks Peter,
I completely agree with that change!
Let me update the patch.


> 
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -457,13 +457,20 @@ static void kprobe_emulate_call(struct k
>  }
>  NOKPROBE_SYMBOL(kprobe_emulate_call);
>  
> -static void kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs)
> +static __always_inline 
> +void __kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs, bool cond)
>  {
>  	unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
>  
> -	ip += p->ainsn.rel32;
> +	if (cond)
> +		ip += p->ainsn.rel32;
>  	int3_emulate_jmp(regs, ip);
>  }
> +
> +static void kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs)
> +{
> +	__kprobe_emulate_jmp(p, regs, true);
> +}
>  NOKPROBE_SYMBOL(kprobe_emulate_jmp);
>  
>  static const unsigned long jcc_mask[6] = {
> @@ -488,10 +495,7 @@ static void kprobe_emulate_jcc(struct kp
>  		if (p->ainsn.jcc.type >= 0xe)
>  			match = match && (regs->flags & X86_EFLAGS_ZF);
>  	}
> -	if ((match && !invert) || (!match && invert))
> -		kprobe_emulate_jmp(p, regs);
> -	else
> -		regs->ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
> +	__kprobe_emulate_jmp(p, regs, (match && !invert) || (!match && invert));
>  }
>  NOKPROBE_SYMBOL(kprobe_emulate_jcc);
>  
> @@ -524,10 +528,7 @@ static void kprobe_emulate_loop(struct k
>  	else if (p->ainsn.loop.type == 1)	/* LOOPE */
>  		match = match && (regs->flags & X86_EFLAGS_ZF);
>  
> -	if (match)
> -		kprobe_emulate_jmp(p, regs);
> -	else
> -		regs->ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
> +	__kprobe_emulate_jmp(p, regs, match);
>  }
>  NOKPROBE_SYMBOL(kprobe_emulate_loop);
>  
> @@ -613,6 +614,12 @@ static int prepare_emulation(struct kpro
>  		else
>  			p->ainsn.rel32 = *(s32 *)&insn->immediate.value;
>  		break;
> +	case 0x70 ... 0x7f:
> +		/* 1 byte conditional jump */
> +		p->ainsn.emulate_op = kprobe_emulate_jcc;
> +		p->ainsn.jcc.type = opcode & 0xf;
> +		p->ainsn.rel32 = *(char *)insn->immediate.bytes;
> +		break;
>  	case 0x0f:
>  		opcode = insn->opcode.bytes[1];
>  		if ((opcode & 0xf0) == 0x80) {
> @@ -667,12 +674,7 @@ static int prepare_emulation(struct kpro
>  #endif
>  		break;
>  	default:
> -		if ((opcode & 0xf0) == 0x70) {
> -			/* 1 byte conditional jump */
> -			p->ainsn.emulate_op = kprobe_emulate_jcc;
> -			p->ainsn.jcc.type = opcode & 0xf;
> -			p->ainsn.rel32 = *(char *)insn->immediate.bytes;
> -		}
> +		break;
>  	}
>  	p->ainsn.size = insn->length;
>  


-- 
Masami Hiramatsu <mhiramat@...nel.org>