[PATCH 2/2] uprobes: x86: Prohibit probing on MOV SS instruction

[Masami Hiramatsu]

Since MOV SS and POP SS instructions will delay the exceptions
until the next instruction is executed, we should not do
single-stepping on it by uprobes.

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 <mhiramat@xxxxxxxxxx>
---
 arch/x86/kernel/uprobes.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 85c7ef23d99f..c84bb5396958 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/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