kprobes/x86: Prohibit probing on exception masking instructions
authorMasami Hiramatsu <mhiramat@kernel.org>
Wed, 9 May 2018 12:58:15 +0000 (21:58 +0900)
committerThomas Gleixner <tglx@linutronix.de>
Sun, 13 May 2018 17:52:55 +0000 (19:52 +0200)
commitee6a7354a3629f9b65bc18dbe393503e9440d6f5
treef12478e840fccf8f714f9315326065d440b46b7e
parenta466ef76b815b86748d9870ef2a430af7b39c710
kprobes/x86: Prohibit probing on exception masking instructions

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

However, kprobes usually executes those instructions directly on trampoline
buffer (a.k.a. kprobe-booster), except for the kprobes which has
post_handler. Thus if kprobe user probes MOV SS with post_handler, it will
do single-stepping on the MOV SS.

This means it is safe that if it is used via ftrace or perf/bpf since those
don't use the post_handler.

Anyway, since the stack switching is a rare case, it is safer just
rejecting kprobes on such instructions.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Francis Deslauriers <francis.deslauriers@efficios.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Yonghong Song <yhs@fb.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "David S . Miller" <davem@davemloft.net>
Link: https://lkml.kernel.org/r/152587069574.17316.3311695234863248641.stgit@devbox
arch/x86/include/asm/insn.h
arch/x86/kernel/kprobes/core.c