linux-kernel - Re: [PATCH 3/3] kprobes/x86: Simplify indirect-jump check in retpoline

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Message-ID: <20181030083650.GB1459@hirez.programming.kicks-ass.net>
Date:   Tue, 30 Oct 2018 09:36:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc:     Linux-Kernel <linux-kernel@...r.kernel.org>, mingo@...hat.com,
        konrad.wilk@...cle.com, dwmw@...zon.co.uk, tglx@...utronix.de,
        Srinivas REDDY Eeda <srinivas.eeda@...cle.com>, bp@...e.de,
        hpa@...or.com
Subject: Re: [PATCH 3/3] kprobes/x86: Simplify indirect-jump check in
 retpoline

On Mon, Oct 29, 2018 at 11:55:06PM -0700, Zhenzhong Duan wrote:
> Since CONFIG_RETPOLINE hard depends on compiler support now, so
> replacing indirect-jump check with the range check is safe in that case.

Can we put kprobes on module init text before we run alternatives on it?

> @@ -240,20 +242,16 @@ static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
>  
>  static int insn_is_indirect_jump(struct insn *insn)
>  {
> -	int ret = __insn_is_indirect_jump(insn);
> +	int ret;
>  
>  #ifdef CONFIG_RETPOLINE
> -	/*
> -	 * Jump to x86_indirect_thunk_* is treated as an indirect jump.
> -	 * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
> -	 * older gcc may use indirect jump. So we add this check instead of
> -	 * replace indirect-jump check.
> -	 */
> -	if (!ret)
> +	/* Jump to x86_indirect_thunk_* is treated as an indirect jump. */
>  		ret = insn_jump_into_range(insn,
>  				(unsigned long)__indirect_thunk_start,
>  				(unsigned long)__indirect_thunk_end -
>  				(unsigned long)__indirect_thunk_start);
> +#else
> +		ret = __insn_is_indirect_jump(insn);
>  #endif
>  	return ret;
>  }

The resulting code is indented wrong.