linux-kernel - Re: [PATCH] uprobes/x86: allow to probe a "nop" insn with 0x66 prefix

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Message-Id: <20221202073002.cae85d5ff0c80b1a3b8b67b4@kernel.org>
Date:   Fri, 2 Dec 2022 07:30:02 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Seiji Nishikawa <snishika@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] uprobes/x86: allow to probe a "nop" insn with 0x66
 prefix

On Thu, 1 Dec 2022 15:26:44 +0100
Oleg Nesterov <oleg@...hat.com> wrote:

> From: Denys Vlasenko <dvlasenk@...hat.com>
> 
> Intel icc -hotpatch inserts 2-byte "0x66 0x90" NOP at the start of each
> function to reserve extra space for hot-patching, and currently it is not
> possible to probe these functions because branch_setup_xol_ops() wrongly
> nacks NOP with REP prefix.

Looks good to me.

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

Thank you!

> 
> Fixes: 250bbd12c2fe ("uprobes/x86: Refuse to attach uprobe to "word-sized" branch insns")
> Reported-by: Seiji Nishikawa <snishika@...hat.com>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  arch/x86/kernel/uprobes.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index b63cf8f7745e..6c07f6daaa22 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -722,8 +722,9 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
>  	switch (opc1) {
>  	case 0xeb:	/* jmp 8 */
>  	case 0xe9:	/* jmp 32 */
> -	case 0x90:	/* prefix* + nop; same as jmp with .offs = 0 */
>  		break;
> +	case 0x90:	/* prefix* + nop; same as jmp with .offs = 0 */
> +		goto setup;
>  
>  	case 0xe8:	/* call relative */
>  		branch_clear_offset(auprobe, insn);
> @@ -753,6 +754,7 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
>  			return -ENOTSUPP;
>  	}
>  
> +setup:
>  	auprobe->branch.opc1 = opc1;
>  	auprobe->branch.ilen = insn->length;
>  	auprobe->branch.offs = insn->immediate.value;
> -- 
> 2.25.1.362.g51ebf55
> 
> 


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