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x86/kprobes: Identify far indirect JMP correctly

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Since Grp5 far indirect JMP is FF "mod 101 r/m", it should be
(modrm & 0x38) == 0x28, and near indirect JMP is also 0x38 == 0x20.
So we can mask modrm with 0x30 and check 0x20.
This is actually what the original code does, it also doesn't care
the last bit. So the result code is same.

Thus, I think this is just a cosmetic cleanup.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/161469873475.49483.13257083019966335137.stgit@devnote2
This commit is contained in:
Masami Hiramatsu 2021-03-03 00:25:34 +09:00 • committed by Peter Zijlstra
parent d60ad3d46f
commit a194acd316
1 changed files with 1 additions and 2 deletions
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3
arch/x86/kernel/kprobes/core.c
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@ -467,8 +467,7 @@ static void set_resume_flags(struct kprobe *p, struct insn *insn)
p->ainsn.is_call = 1;
p->ainsn.is_abs_ip = 1;
break;
} else if (((opcode & 0x31) == 0x20) ||
((opcode & 0x31) == 0x21)) {
} else if ((opcode & 0x30) == 0x20) {
/*
* jmp near and far, absolute indirect
* ip is correct.