From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 92DF4C432C0 for ; Fri, 22 Nov 2019 11:20:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6838120708 for ; Fri, 22 Nov 2019 11:20:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574421632; bh=cr3IUombf9EhZ71/I7ho4fT1dibD1bo/zsPTJKKMmA8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=tnTep0rS50qTixnVRz/MpPws25V8WGFSG1SD6UxfOEKqm6E0YiJ275OmBkb7Mi8wG omebaGV/RaXzMzZ2f/LQ0vjfDFAzSTRajHFEMP6BKI8XF/mTU3GwIecW/dupLVswPl 3URJEvv5fQxTMTgUN9ucYg3W0hXYJakzTOOZJzTY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729716AbfKVLUb (ORCPT ); Fri, 22 Nov 2019 06:20:31 -0500 Received: from mail.kernel.org ([198.145.29.99]:52558 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727944AbfKVKpy (ORCPT ); Fri, 22 Nov 2019 05:45:54 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E4EA320715; Fri, 22 Nov 2019 10:45:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574419553; bh=cr3IUombf9EhZ71/I7ho4fT1dibD1bo/zsPTJKKMmA8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=yeyHu9jYJwigy7B3F99Wz2oytgOFIUcON5aQJDObFdyvScsqWe0usVWk/jfaZQrSG efuTaRqMKxLU/bd0qAkPa/h4H+b338Jtz0m5Hd2TMOsZCBTtLtVNcYIlPMalFMYAQi xKIefxytrPafGOEvxCMdaZLEXH4y3JPAUwbp0l7U= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Masami Hiramatsu , Thomas Gleixner , Ricardo Neri , Francis Deslauriers , Oleg Nesterov , Alexei Starovoitov , Steven Rostedt , Andy Lutomirski , "H . Peter Anvin" , Yonghong Song , Borislav Petkov , Linus Torvalds , "David S . Miller" Subject: [PATCH 4.9 150/222] kprobes/x86: Prohibit probing on exception masking instructions Date: Fri, 22 Nov 2019 11:28:10 +0100 Message-Id: <20191122100913.582883301@linuxfoundation.org> X-Mailer: git-send-email 2.24.0 In-Reply-To: <20191122100830.874290814@linuxfoundation.org> References: <20191122100830.874290814@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Masami Hiramatsu commit ee6a7354a3629f9b65bc18dbe393503e9440d6f5 upstream. 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 Signed-off-by: Thomas Gleixner Cc: Ricardo Neri Cc: Francis Deslauriers Cc: Oleg Nesterov Cc: Alexei Starovoitov Cc: Steven Rostedt Cc: Andy Lutomirski Cc: "H . Peter Anvin" Cc: Yonghong Song Cc: Borislav Petkov Cc: Linus Torvalds Cc: "David S . Miller" Link: https://lkml.kernel.org/r/152587069574.17316.3311695234863248641.stgit@devbox Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/insn.h | 18 ++++++++++++++++++ arch/x86/kernel/kprobes/core.c | 4 ++++ 2 files changed, 22 insertions(+) --- a/arch/x86/include/asm/insn.h +++ b/arch/x86/include/asm/insn.h @@ -208,4 +208,22 @@ static inline int insn_offset_immediate( 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 */ --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -376,6 +376,10 @@ int __copy_instruction(u8 *dest, u8 *src return 0; memcpy(dest, insn.kaddr, length); + /* We should not singlestep on the exception masking instructions */ + if (insn_masking_exception(&insn)) + return 0; + #ifdef CONFIG_X86_64 if (insn_rip_relative(&insn)) { s64 newdisp;