linux-kernel - [RFC PATCH v3 03/26] kprobes: x86: mark 2 bytes NOP as boostable.

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Date:	Fri, 13 Feb 2015 13:40:24 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	<linux@....linux.org.uk>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<hpa@...or.com>, <rostedt@...dmis.org>, <ananth@...ibm.com>,
	<anil.s.keshavamurthy@...el.com>, <davem@...emloft.net>,
	<masami.hiramatsu.pt@...achi.com>, <luto@...capital.net>,
	<keescook@...omium.org>, <oleg@...hat.com>, <wangnan0@...wei.com>,
	<dave.long@...aro.org>, <tixy@...aro.org>, <nico@...aro.org>,
	<yalin.wang2010@...il.com>, <catalin.marinas@....com>,
	<Yalin.Wang@...ymobile.com>, <mark.rutland@....com>,
	<dave.hansen@...ux.intel.com>, <jkenisto@...ibm.com>,
	<anton@...ba.org>, <stefani@...bold.net>, <JBeulich@...e.com>,
	<akpm@...ux-foundation.org>, <rusty@...tcorp.com.au>,
	<peterz@...radead.org>, <prarit@...hat.com>, <fabf@...net.be>,
	<hannes@...xchg.org>
CC:	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <lizefan@...wei.com>
Subject: [RFC PATCH v3 03/26] kprobes: x86: mark 2 bytes NOP as boostable.

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 which is able 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 */
-- 
1.8.4

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