[PATCH 4.9 151/222] uprobes/x86: Prohibit probing on MOV SS instruction

From: Greg Kroah-Hartman
Date: Fri Nov 22 2019 - 06:20:27 EST

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

commit 13ebe18c94f5b0665c01ae7fad2717ae959f4212 upstream.

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

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>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
Cc: Francis Deslauriers <francis.deslauriers@xxxxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: Yonghong Song <yhs@xxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: "David S . Miller" <davem@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/152587072544.17316.5950935243917346341.stgit@devbox
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/x86/kernel/uprobes.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -296,6 +296,10 @@ static int uprobe_init_insn(struct arch_
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;