Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756653AbdCHBEl (ORCPT ); Tue, 7 Mar 2017 20:04:41 -0500 Received: from mga02.intel.com ([134.134.136.20]:20029 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751174AbdCHBEj (ORCPT ); Tue, 7 Mar 2017 20:04:39 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,261,1486454400"; d="scan'208";a="1105982592" 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 , Arnaldo Carvalho de Melo , Adrian Hunter , Kees Cook , Thomas Garnier , Dmitry Vyukov Subject: [v6 PATCH 10/21] x86/insn-eval: Do not use R/EBP as base if mod in ModRM is zero Date: Tue, 7 Mar 2017 16:32:43 -0800 Message-Id: <20170308003254.27833-11-ricardo.neri-calderon@linux.intel.com> X-Mailer: git-send-email 2.9.3 In-Reply-To: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> References: <20170308003254.27833-1-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: 3263 Lines: 80 Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when the mod part of the ModRM byte is zero and R/EBP is specified in the R/M part of such bit, the value of the aforementioned register should not be used in the address computation. Instead, a 32-bit displacement is expected. The instruction decoder takes care of setting the displacement to the expected value. Returning -EDOM signals callers that they should ignore the value of such register when computing the address encoded in the instruction operands. Also, callers should exercise care to correctly interpret this particular case. In IA-32e 64-bit mode, the address is given by the displacement plus the value of the RIP. In IA-32e compatibility mode, the value of EIP is ignored. This correction is done for our insn_get_addr_ref. Cc: Dave Hansen Cc: Adam Buchbinder Cc: Colin Ian King Cc: Lorenzo Stoakes Cc: Qiaowei Ren Cc: Arnaldo Carvalho de Melo Cc: Masami Hiramatsu Cc: Adrian Hunter Cc: Kees Cook Cc: Thomas Garnier Cc: Peter Zijlstra Cc: Borislav Petkov Cc: Dmitry Vyukov Cc: Ravi V. Shankar Cc: x86@kernel.org Signed-off-by: Ricardo Neri --- arch/x86/lib/insn-eval.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index cda6c71..ea10b03 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -250,6 +250,14 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, switch (type) { case REG_TYPE_RM: regno = X86_MODRM_RM(insn->modrm.value); + /* if mod=0, register R/EBP is not used in the address + * computation. Instead, a 32-bit displacement is expected; + * the instruction decoder takes care of reading such + * displacement. This is true for both R/EBP and R13, as the + * REX.B bit is not decoded. + */ + if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0) + return -EDOM; if (X86_REX_B(insn->rex_prefix.value)) regno += 8; break; @@ -599,9 +607,22 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) eff_addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); - if (addr_offset < 0) + /* -EDOM means that we must ignore the address_offset. + * The only case in which we see this value is when + * R/M points to R/EBP. In such a case, in 64-bit mode + * the effective address is relative to tho RIP. + */ + if (addr_offset == -EDOM) { + eff_addr = 0; +#ifdef CONFIG_X86_64 + if (user_64bit_mode(regs)) + eff_addr = (long)regs->ip; +#endif + } else if (addr_offset < 0) { goto out_err; - eff_addr = regs_get_register(regs, addr_offset); + } else { + eff_addr = regs_get_register(regs, addr_offset); + } } eff_addr += insn->displacement.value; } -- 2.9.3