linux-kernel - Re: [PATCH 1/2] x86/kprobes: Fix kprobes instruction boudary check with CONFIG

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Date:   Wed, 7 Sep 2022 18:12:18 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Suleiman Souhlal <suleiman@...gle.com>,
        bpf <bpf@...r.kernel.org>, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Subject: Re: [PATCH 1/2] x86/kprobes: Fix kprobes instruction boudary check
 with CONFIG_RETHUNK

On Wed, 7 Sep 2022 09:06:44 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Sep 07, 2022 at 09:55:21AM +0900, Masami Hiramatsu (Google) wrote:
> 
> > +/* Return the jump target address or 0 */
> > +static inline unsigned long insn_get_branch_addr(struct insn *insn)
> > +{
> > +	switch (insn->opcode.bytes[0]) {
> > +	case 0xe0:	/* loopne */
> > +	case 0xe1:	/* loope */
> > +	case 0xe2:	/* loop */
> 
> Oh cute, objtool doesn't know about those, let me go add them.
> 
> > +	case 0xe3:	/* jcxz */
> > +	case 0xe9:	/* near relative jump */
> 
>  /* JMP.d32 */
> 
> > +	case 0xeb:	/* short relative jump */
> 
>  /* JMP.d8 */
> 
> > +		break;
> > +	case 0x0f:
> > +		if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
> 
>  /* Jcc.d32 */
> 
> Are the GNU AS names for these things.

OK, it should be updated. Where can I refer the names (especially '.dX' suffixes)?

> 
> > +			break;
> > +		return 0;
> 
> > +	default:
> > +		if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
> > +			break;
> > +		return 0;
> 
> You could write that as:
> 
> 	case 0x70 ... 0x7f: /* Jcc.d8 */
> 		break;
> 
> 	default:
> 		return 0;

Thanks! I'll update it.

> 
> > +	}
> > +	return (unsigned long)insn->next_byte + insn->immediate.value;
> > +}
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>