linux-kernel - Re: [PATCH][RESEND] kprobes: x86: mark 2 bytes NOP as boostable.

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Date:	Wed, 11 Feb 2015 12:18:55 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	<masami.hiramatsu.pt@...achi.com>, <mingo@...hat.com>,
	<tglx@...utronix.de>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, <lizefan@...wei.com>
Subject: Re: [PATCH][RESEND] kprobes: x86: mark 2 bytes NOP as boostable.

Hi Andrew,

Could you please queue this patch onto your -mm tree? Masami has given an Acked-by already.

Thank you!

On 2015/2/10 9:34, Wang Nan wrote:
> Currently, x86 kprobes is unable to boost 2 bytes nop like:
> 
> nopl 0x0(%rax,%rax,1)
> 
> which is 0x0f 0x1f 0x44 0x00 0x00.
> 
> Such nops have exactly 5 bytes to hold a relative jmp instruction.
> Boosting them should be obviously safe.
> 
> This patch enable boosting such nops by simply updating
> twobyte_is_boostable[] array.
> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> ---
>  arch/x86/kernel/kprobes/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 98f654d..6a1146e 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -84,7 +84,7 @@ static volatile u32 twobyte_is_boostable[256 / 32] = {
>  	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f          */
>  	/*      ----------------------------------------------          */
>  	W(0x00, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0) | /* 00 */
> -	W(0x10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 10 */
> +	W(0x10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1) , /* 10 */
>  	W(0x20, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 20 */
>  	W(0x30, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 30 */
>  	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
> 


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