linux-kernel - Re: [PATCH] uprobes: use BX register for rip-relative fixups, not AX

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Date:	Wed, 30 Apr 2014 17:29:58 -0700
From:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] uprobes: use BX register for rip-relative fixups, not
 AX

On Mon, 2014-04-28 at 19:06 +0200, Denys Vlasenko wrote:
> Otherwise, instructions such as cmpxchg and div will be mishandled.
> 
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Jim Keniston <jkenisto@...ibm.com>
> CC: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> CC: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> CC: Ingo Molnar <mingo@...nel.org>
> CC: Oleg Nesterov <oleg@...hat.com>
> ---
>  arch/x86/kernel/uprobes.c | 57 ++++++++++++++++++++++++++++++-----------------
>  1 file changed, 37 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
...
> @@ -296,41 +296,58 @@ static void riprel_analyze(struct arch_uprobe *auprobe, struct insn *insn)
>  	 */
>  	cursor = auprobe->insn + insn_offset_modrm(insn);
>  	/*
> -	 * Convert from rip-relative addressing to register-relative addressing
> -	 * via a scratch register.
> +	 * Convert from rip-relative addressing
> +	 * to register-relative addressing via a scratch register.
>  	 */

This comment looks like a regression. :-)

Looks good otherwise (setting aside your later findings about cmpxchg8b
and such -- I guess we need some way to helpfully reject rip-relative
forms of such instructions).

Reviewed-by: Jim Keniston <jkenisto@...ibm.com>

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