linux-kernel - [PATCH 5.10 3/9] x86/kprobes: Retrieve correct opcode for group instruction

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Message-ID: <20230705064653.226811-4-lihuafei1@huawei.com>
Date:   Wed, 5 Jul 2023 14:46:47 +0800
From:   Li Huafei <lihuafei1@...wei.com>
To:     <stable@...r.kernel.org>
CC:     <gregkh@...uxfoundation.org>, <mhiramat@...nel.org>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <x86@...nel.org>, <hpa@...or.com>, <sashal@...nel.org>,
        <peterz@...radead.org>, <linux-kernel@...r.kernel.org>,
        <xukuohai@...wei.com>, <natechancellor@...il.com>,
        <ndesaulniers@...gle.com>, <rostedt@...dmis.org>,
        <weiyongjun1@...wei.com>, <gustavoars@...nel.org>,
        <namit@...are.com>, <laijs@...ux.alibaba.com>,
        <clang-built-linux@...glegroups.com>, <lihuafei1@...wei.com>
Subject: [PATCH 5.10 3/9] x86/kprobes: Retrieve correct opcode for group instruction

From: Masami Hiramatsu <mhiramat@...nel.org>

[ Upstream commit d60ad3d46f1d04a282c56159f1deb675c12733fd ]

Since the opcodes start from 0xff are group5 instruction group which is
not 2 bytes opcode but the extended opcode determined by the MOD/RM byte.

The commit abd82e533d88 ("x86/kprobes: Do not decode opcode in resume_execution()")
used insn->opcode.bytes[1], but that is not correct. We have to refer
the insn->modrm.bytes[1] instead.

Fixes: abd82e533d88 ("x86/kprobes: Do not decode opcode in resume_execution()")
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/161469872400.49483.18214724458034233166.stgit@devnote2
Signed-off-by: Li Huafei <lihuafei1@...wei.com>
---
 arch/x86/kernel/kprobes/core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 19ca5164be4d..40d5c603ce8e 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -464,7 +464,11 @@ static void set_resume_flags(struct kprobe *p, struct insn *insn)
 		break;
 #endif
 	case 0xff:
-		opcode = insn->opcode.bytes[1];
+		/*
+		 * Since the 0xff is an extended group opcode, the instruction
+		 * is determined by the MOD/RM byte.
+		 */
+		opcode = insn->modrm.bytes[0];
 		if ((opcode & 0x30) == 0x10) {
 			/*
 			 * call absolute, indirect
-- 
2.17.1