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x86/kprobes: Retrieve correct opcode for group instruction

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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 abd82e533d ("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: abd82e533d ("x86/kprobes: Do not decode opcode in resume_execution()")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/161469872400.49483.18214724458034233166.stgit@devnote2
This commit is contained in:
Masami Hiramatsu 2021-03-03 00:25:24 +09:00 committed by Peter Zijlstra
parent 0705ef64d1
commit d60ad3d46f
1 changed files with 5 additions and 1 deletions
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6
arch/x86/kernel/kprobes/core.c
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@ -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