From: Masami Hiramatsu mhiramat@kernel.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@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/161469872400.49483.18214724458034233166.stgit@devn... Signed-off-by: Sasha Levin sashal@kernel.org --- 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 df776cdca327..08674e7a5d7b 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -448,7 +448,11 @@ 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