x86: kprobes: Prohibit probing on instruction which has emulate prefix

Prohibit probing on instruction which has XEN_EMULATE_PREFIX
or KVM's emulate prefix. Since that prefix is a marker for Xen
and KVM, if we modify the marker by kprobe's int3, that doesn't
work as expected.

Signed-off-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: [email protected]
Cc: Boris Ostrovsky <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Stefano Stabellini <[email protected]>
Cc: Andrew Cooper <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: [email protected]
Cc: Randy Dunlap <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Link: https://lkml.kernel.org/r/156777566048.25081.6296162369492175325.stgit@devnote2

Author: mhiramat

arch/x86/kernel/kprobes/core.c

@@ -351,6 +351,10 @@ int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn)
 	kernel_insn_init(insn, dest, MAX_INSN_SIZE);
 	insn_get_length(insn);
 
+	/* We can not probe force emulate prefixed instruction */
+	if (insn_has_emulate_prefix(insn))
+		return 0;
+
 	/* Another subsystem puts a breakpoint, failed to recover */
 	if (insn->opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
 		return 0;