Commit d60ad3d4 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Peter Zijlstra
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x86/kprobes: Retrieve correct opcode for group instruction 



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 abd82e53 ("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: abd82e53 ("x86/kprobes: Do not decode opcode in resume_execution()")
Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/161469872400.49483.18214724458034233166.stgit@devnote2
parent 0705ef64

arch/x86/kernel/kprobes/core.c

+5 −1
Original line number Diff line number Diff line
@@ -453,7 +453,11 @@ 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