Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1038172AbdDULAr (ORCPT ); Fri, 21 Apr 2017 07:00:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:47797 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1035223AbdDULAp (ORCPT ); Fri, 21 Apr 2017 07:00:45 -0400 Date: Fri, 21 Apr 2017 12:52:58 +0200 From: Borislav Petkov To: Ricardo Neri Cc: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Andrew Morton , Brian Gerst , Chris Metcalf , Dave Hansen , Paolo Bonzini , 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, Adam Buchbinder , Colin Ian King , Lorenzo Stoakes , Qiaowei Ren , Arnaldo Carvalho de Melo , Adrian Hunter , Kees Cook , Thomas Garnier , Dmitry Vyukov Subject: Re: [v6 PATCH 10/21] x86/insn-eval: Do not use R/EBP as base if mod in ModRM is zero Message-ID: <20170421105258.q4vqrephtm7t3h4c@pd.tnic> References: <20170308003254.27833-1-ricardo.neri-calderon@linux.intel.com> <20170308003254.27833-11-ricardo.neri-calderon@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170308003254.27833-11-ricardo.neri-calderon@linux.intel.com> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4793 Lines: 139 On Tue, Mar 07, 2017 at 04:32:43PM -0800, Ricardo Neri wrote: > 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. > + */ I'd simply write here: "ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit displacement is following." In addition, kernel comments style is: /* * A sentence ending with a full-stop. * Another sentence. ... * More sentences. ... */ > + if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0) > + return -EDOM; if (X86_MODRM_MOD(insn->modrm.value) == 0 && X86_MODRM_RM(insn->modrm.value) == 5) looks more understandable to me. > 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. s/tho// > + */ Kernel comments style is: /* * A sentence ending with a full-stop. * Another sentence. ... * More sentences. ... */ > + if (addr_offset == -EDOM) { > + eff_addr = 0; > +#ifdef CONFIG_X86_64 > + if (user_64bit_mode(regs)) > + eff_addr = (long)regs->ip; Is regs->ip the rIP of the *following* insn? > +#endif You can do this in a prepatch and then get rid of the ifdeffery here: diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index 2b5d686ea9f3..f6239273c5f1 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -115,9 +115,9 @@ static inline int v8086_mode(struct pt_regs *regs) #endif } -#ifdef CONFIG_X86_64 static inline bool user_64bit_mode(struct pt_regs *regs) { +#ifdef CONFIG_X86_64 #ifndef CONFIG_PARAVIRT /* * On non-paravirt systems, this is the only long mode CPL 3 @@ -128,6 +128,9 @@ static inline bool user_64bit_mode(struct pt_regs *regs) /* Headers are too twisted for this to go in paravirt.h. */ return regs->cs == __USER_CS || regs->cs == pv_info.extra_user_64bit_cs; #endif +#else /* !CONFIG_X86_64 */ + return false; +#endif } #define current_user_stack_pointer() current_pt_regs()->sp --- -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --