uprobes/x86: Prohibit probing on MOV SS instruction

Since MOV SS and POP SS instructions will delay the exceptions until the
next instruction is executed, single-stepping on it by uprobes must be
prohibited.

uprobe already rejects probing on POP SS (0x1f), but allows probing on MOV
SS (0x8e and reg == 2).  This checks the target instruction and if it is
MOV SS or POP SS, returns -ENOTSUPP to reject probing.

Signed-off-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Cc: Ricardo Neri <[email protected]>
Cc: Francis Deslauriers <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: "H . Peter Anvin" <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: "David S . Miller" <[email protected]>
Link: https://lkml.kernel.org/r/152587072544.17316.5950935243917346341.stgit@devbox

Author: mhiramat

arch/x86/kernel/uprobes.c

@@ -299,6 +299,10 @@ static int uprobe_init_insn(struct arch_uprobe *auprobe, struct insn *insn, bool
 	if (is_prefix_bad(insn))
 		return -ENOTSUPP;
 
+	/* We should not singlestep on the exception masking instructions */
+	if (insn_masking_exception(insn))
+		return -ENOTSUPP;
+
 	if (x86_64)
 		good_insns = good_insns_64;
 	else