Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752588AbdHSAed (ORCPT ); Fri, 18 Aug 2017 20:34:33 -0400 Received: from mga07.intel.com ([134.134.136.100]:43538 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751726AbdHSA2j (ORCPT ); Fri, 18 Aug 2017 20:28:39 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.41,394,1498546800"; d="scan'208";a="1164119661" 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 , "Ravi V. Shankar" , Shuah Khan , linux-kernel@vger.kernel.org, x86@kernel.org, ricardo.neri@intel.com, Ricardo Neri , Adam Buchbinder , Colin Ian King , Lorenzo Stoakes , Qiaowei Ren , Nathan Howard , Adan Hawthorn , Joe Perches Subject: [PATCH v8 06/28] x86/mpx: Do not use SIB.index if its value is 100b and ModRM.mod is not 11b Date: Fri, 18 Aug 2017 17:27:47 -0700 Message-Id: <20170819002809.111312-7-ricardo.neri-calderon@linux.intel.com> X-Mailer: git-send-email 2.13.0 In-Reply-To: <20170819002809.111312-1-ricardo.neri-calderon@linux.intel.com> References: <20170819002809.111312-1-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: 3621 Lines: 96 Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when ModRM.mod !=11b and ModRM.rm = 100b indexed register-indirect addressing is used. In other words, a SIB byte follows the ModRM byte. In the specific case of SIB.index = 100b, the scale*index portion of the computation of the effective address is null. To signal callers of this particular situation, get_reg_offset() can return -EDOM (-EINVAL continues to indicate that an error when decoding the SIB byte). An example of this situation can be the following instruction: 8b 4c 23 80 mov -0x80(%rbx,%riz,1),%rcx ModRM: 0x4c [mod:1b][reg:1b][rm:100b] SIB: 0x23 [scale:0b][index:100b][base:11b] Displacement: 0x80 (1-byte, as per ModRM.mod = 1b) The %riz 'register' indicates a null index. In long mode, a REX prefix may be used. When a REX prefix is present, REX.X adds a fourth bit to the register selection of SIB.index. This gives the ability to refer to all the 16 general purpose registers. When REX.X is 1b and SIB.index is 100b, the index is indicated in %r12. In our example, this would look like: 42 8b 4c 23 80 mov -0x80(%rbx,%r12,1),%rcx REX: 0x42 [W:0b][R:0b][X:1b][B:0b] ModRM: 0x4c [mod:1b][reg:1b][rm:100b] SIB: 0x23 [scale:0b][.X: 1b, index:100b][.B:0b, base:11b] Displacement: 0x80 (1-byte, as per ModRM.mod = 1b) %r12 is a valid register to use in the scale*index part of the effective address computation. Cc: Borislav Petkov Cc: Andy Lutomirski 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 | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 9eec98022510..892aa6468805 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -110,6 +110,15 @@ 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 ModRM.mod != 3 and SIB.index = 4 the scale*index + * portion of the address computation is null. This is + * true only if REX.X is 0. In such a case, the SIB index + * is used in the address computation. + */ + if (X86_MODRM_MOD(insn->modrm.value) != 3 && regno == 4) + return -EDOM; break; case REG_TYPE_BASE: @@ -160,11 +169,20 @@ 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 (indx_offset == -EDOM) + indx = 0; + else if (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 { -- 2.13.0