Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752584AbdCCVr3 (ORCPT ); Fri, 3 Mar 2017 16:47:29 -0500 Received: from mga01.intel.com ([192.55.52.88]:25157 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752237AbdCCVrQ (ORCPT ); Fri, 3 Mar 2017 16:47:16 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,238,1484035200"; d="scan'208";a="64033522" From: Ricardo Neri To: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov Cc: Peter Zijlstra , Andrew Morton , Brian Gerst , Chris Metcalf , Dave Hansen , Paolo Bonzini , Liang Z Li , Masami Hiramatsu , Huang Rui , Jiri Slaby , Jonathan Corbet , "Michael S. Tsirkin" , Paul Gortmaker , Vlastimil Babka , Chen Yucong , Alexandre Julliard , Stas Sergeev , Fenghua Yu , "Ravi V. Shankar" , Shuah Khan , linux-kernel@vger.kernel.org, x86@kernel.org, linux-msdos@vger.kernel.org, wine-devel@winehq.org, Ricardo Neri , Adam Buchbinder , Colin Ian King , Lorenzo Stoakes , Qiaowei Ren , Nathan Howard , Adan Hawthorn , Joe Perches Subject: [v5 02/20] x86/mpx: Do not use SIB index if index points to R/ESP Date: Fri, 3 Mar 2017 13:41:14 -0800 Message-Id: <20170303214132.77244-3-ricardo.neri-calderon@linux.intel.com> X-Mailer: git-send-email 2.9.3 In-Reply-To: <20170303214132.77244-1-ricardo.neri-calderon@linux.intel.com> References: <20170303214132.77244-1-ricardo.neri-calderon@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3193 Lines: 88 Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when memory addressing is used (i.e., mod part of ModR/M is not 3), a SIB byte is used and the index of the SIB byte points to the R/ESP (i.e., index = 4), the index should not be used in the computation of the memory address. In these cases the address is simply the value present in the register pointed by the base part of the SIB byte plus the displacement byte. An example of such instruction could be insn -0x80(%rsp) This is represented as: [opcode] 4c 23 80 ModR/M=0x4c: mod: 0x1, reg: 0x1: r/m: 0x4(R/ESP) SIB=0x23: sc: 0, index: 0x100(R/ESP), base: 0x11(R/EBX): Displacement -0x80 The correct address is (base) + displacement; no index is used. We can achieve the desired effect of not using the index by making get_reg_offset return -EDOM in this particular case. This value indicates callers that they should not use the index to calculate the address. EINVAL continues to indicate that an error when decoding the SIB byte. Care is taken to allow R12 to be used as index, which is a valid scenario. Cc: Dave Hansen Cc: Adam Buchbinder Cc: Colin Ian King Cc: Lorenzo Stoakes Cc: Qiaowei Ren Cc: Peter Zijlstra Cc: Nathan Howard Cc: Adan Hawthorn Cc: Joe Perches Cc: Ravi V. Shankar Cc: x86@kernel.org Signed-off-by: Ricardo Neri --- arch/x86/mm/mpx.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index ff112e3..d9e92d6 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -110,6 +110,13 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, regno = X86_SIB_INDEX(insn->sib.value); if (X86_REX_X(insn->rex_prefix.value)) regno += 8; + /* + * If mod !=3, register R/ESP (regno=4) is not used as index in + * the address computation. Check is done after looking at REX.X + * This is because R12 (regno=12) can be used as an index. + */ + if (regno == 4 && X86_MODRM_MOD(insn->modrm.value) != 3) + return -EDOM; break; case REG_TYPE_BASE: @@ -159,11 +166,19 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) goto out_err; indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX); - if (indx_offset < 0) + /* + * A negative offset generally means a error, except + * -EDOM, which means that the contents of the register + * should not be used as index. + */ + if (unlikely(indx_offset == -EDOM)) + indx = 0; + else if (unlikely(indx_offset < 0)) goto out_err; + else + indx = regs_get_register(regs, indx_offset); base = regs_get_register(regs, base_offset); - indx = regs_get_register(regs, indx_offset); eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); -- 2.9.3