linux-kernel - [RFC PATCH v2 6/6] uprobes/x86: Emulate rip-relative conditional "near" jmp's

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Message-ID: <20140409194442.GA6245@redhat.com>
Date:	Wed, 9 Apr 2014 21:44:42 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <aarapov@...hat.com>,
	David Long <dave.long@...aro.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Jonathan Lebon <jlebon@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2 6/6] uprobes/x86: Emulate rip-relative conditional
	"near" jmp's

It seems that 16bit condi jmp is just 0x0f + short_jump_opc_plus_0x10.

Reported-by: Jonathan Lebon <jlebon@...hat.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 arch/x86/kernel/uprobes.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index ab9342a..cdad38d 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -588,6 +588,14 @@ static int ttt_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 		ttt_clear_displacement(auprobe, insn);
 		break;
 
+	case 0x0f:
+		if (insn->opcode.nbytes != 2)
+			return -ENOSYS;
+		/*
+		 * If it is a "near" conditional jmp, OPCODE2() - 0x10 matches
+		 * OPCODE1() of the "short" jmp which checks the same condition.
+		 */
+		opc1 = OPCODE2(insn) - 0x10;
 	default:
 		if (!is_cond_jmp_opcode(opc1))
 			return -ENOSYS;
-- 
1.5.5.1

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