Commit-ID: ee6a7354a3629f9b65bc18dbe393503e9440d6f5 Gitweb: https://git.kernel.org/tip/ee6a7354a3629f9b65bc18dbe393503e9440d6f5 Author: Masami Hiramatsu <mhira...@kernel.org> AuthorDate: Wed, 9 May 2018 21:58:15 +0900 Committer: Thomas Gleixner <t...@linutronix.de> CommitDate: Sun, 13 May 2018 19:52:55 +0200
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 <mhira...@kernel.org> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Cc: Ricardo Neri <ricardo.neri-calde...@linux.intel.com> Cc: Francis Deslauriers <francis.deslauri...@efficios.com> Cc: Oleg Nesterov <o...@redhat.com> Cc: Alexei Starovoitov <a...@kernel.org> Cc: Steven Rostedt <rost...@goodmis.org> Cc: Andy Lutomirski <l...@kernel.org> Cc: "H . Peter Anvin" <h...@zytor.com> Cc: Yonghong Song <y...@fb.com> Cc: Borislav Petkov <b...@suse.de> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: "David S . Miller" <da...@davemloft.net> Link: https://lkml.kernel.org/r/152587069574.17316.3311695234863248641.stgit@devbox --- arch/x86/include/asm/insn.h | 18 ++++++++++++++++++ arch/x86/kernel/kprobes/core.c | 4 ++++ 2 files changed, 22 insertions(+) diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h index b3e32b010ab1..c2c01f84df75 100644 --- a/arch/x86/include/asm/insn.h +++ b/arch/x86/include/asm/insn.h @@ -208,4 +208,22 @@ static inline int insn_offset_immediate(struct insn *insn) return insn_offset_displacement(insn) + insn->displacement.nbytes; } +#define POP_SS_OPCODE 0x1f +#define MOV_SREG_OPCODE 0x8e + +/* + * Intel SDM Vol.3A 6.8.3 states; + * "Any single-step trap that would be delivered following the MOV to SS + * instruction or POP to SS instruction (because EFLAGS.TF is 1) is + * suppressed." + * This function returns true if @insn is MOV SS or POP SS. On these + * instructions, single stepping is suppressed. + */ +static inline int insn_masking_exception(struct insn *insn) +{ + return insn->opcode.bytes[0] == POP_SS_OPCODE || + (insn->opcode.bytes[0] == MOV_SREG_OPCODE && + X86_MODRM_REG(insn->modrm.bytes[0]) == 2); +} + #endif /* _ASM_X86_INSN_H */ diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c index 0715f827607c..6f4d42377fe5 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -370,6 +370,10 @@ int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn) if (insn->opcode.bytes[0] == BREAKPOINT_INSTRUCTION) return 0; + /* We should not singlestep on the exception masking instructions */ + if (insn_masking_exception(insn)) + return 0; + #ifdef CONFIG_X86_64 /* Only x86_64 has RIP relative instructions */ if (insn_rip_relative(insn)) {
