From patchwork Thu Jun 15 16:42:54 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Salvatore Mesoraca X-Patchwork-Id: 9789335 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id F3EC060384 for ; Thu, 15 Jun 2017 16:45:24 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E3ECD27E63 for ; Thu, 15 Jun 2017 16:45:24 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D735F280CF; Thu, 15 Jun 2017 16:45:24 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=2.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED,FREEMAIL_FROM,RCVD_IN_DNSWL_HI,T_DKIM_INVALID autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1199E27E63 for ; Thu, 15 Jun 2017 16:45:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751789AbdFOQpK (ORCPT ); Thu, 15 Jun 2017 12:45:10 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:32792 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752582AbdFOQoq (ORCPT ); Thu, 15 Jun 2017 12:44:46 -0400 Received: by mail-wm0-f67.google.com with SMTP id f90so792647wmh.0; Thu, 15 Jun 2017 09:44:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=fFosIB6TXwhnHPJGnpP+0jzlatzsprgEfHSCwEsHc4Y=; b=gWWIP0BSDlAvvLPY8+PH/J+jF9FVe0daHJSq6lWH20cUVPRFtH60YG8nT0ygp56V4n hLjtFX+khx2YHO0KxF3/a2BYJsmwWu4+vogE9igBbDQffgIoQj0ENCB2JAbFhDHtxY7T d8fYIjKb8RaguAja+SKZEMJffot+BO52fOeJIAxN6Wog1L+p+5cNwpsMzDfOQR4d9H81 iCNd3c682ozT538PAWZUGGAfkj+O+b6z7vNjLhkJCg8GhahX5Jkxbnhu+8IRiYVMGOKh QDAJd+8jdtogtE+9Y4ZEpAly0liGrWGaCdP6IlOr0LUBltFWA9NK1gkWZBHdPiJRijpW /GKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=fFosIB6TXwhnHPJGnpP+0jzlatzsprgEfHSCwEsHc4Y=; b=fcPmZGkft8u27xGp02fNY05/he6OdU3fhrStsyKjcVg9n+1RUaZxx3gRdoxVAWr22u EblLF/mqsVDlwYwoKcAcT37IaA2s2xlZYSp6vTfk8YjvEda9FS4PBcNvvml1OfJSqti7 IXXWAHqTeZUgWZijswwuJ/ujGHaNQxxlWytqOfUqAZQYZVD5cKUAYS4f5BAJCVywUy3W ibkuhiXdXt5whwy8Gh6+ksLHvAkNxNKZnNe7OaoaJfqS5fzu62jbfk+xzlMc6O2K4gs0 c3QDCtCxkCAI98nKQI0dQspWnyEV5UnOVwaD8r/ycfSZwSKefQ9alBxrONryVxq34B4s fa0A== X-Gm-Message-State: AKS2vOy+kBzTGExknpFAovUSTyz36Y7Jp763cZ8sYE1gz18P77X4JNYG /CcAn2fp8GFE7FvEGzlOoxRi X-Received: by 10.28.103.193 with SMTP id b184mr4401069wmc.25.1497545079588; Thu, 15 Jun 2017 09:44:39 -0700 (PDT) Received: from localhost ([37.176.236.94]) by smtp.gmail.com with ESMTPSA id k19sm615938wmg.9.2017.06.15.09.44.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 15 Jun 2017 09:44:39 -0700 (PDT) From: Salvatore Mesoraca To: linux-kernel@vger.kernel.org Cc: linux-security-module@vger.kernel.org, kernel-hardening@lists.openwall.com, Salvatore Mesoraca , Brad Spengler , PaX Team , Casey Schaufler , Kees Cook , James Morris , "Serge E. Hallyn" , linux-mm@kvack.org, x86@kernel.org, Jann Horn , Christoph Hellwig , Thomas Gleixner Subject: [RFC v2 7/9] Trampoline emulation Date: Thu, 15 Jun 2017 18:42:54 +0200 Message-Id: <1497544976-7856-8-git-send-email-s.mesoraca16@gmail.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1497544976-7856-1-git-send-email-s.mesoraca16@gmail.com> References: <1497544976-7856-1-git-send-email-s.mesoraca16@gmail.com> Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP Some programs need to generate part of their code at runtime. Luckily enough, in some cases they only generate well-known code sequences (the "trampolines") that can be easily recognized and emulated by the kernel. This way WX Protection can still be active, so a potential attacker won't be able to generate arbitrary sequences of code, but just those that are explicitly allowed. This is not ideal, but it's still better than having WX Protection completely disabled. In particular S.A.R.A. is able to recognize trampolines used by GCC for nested C functions and libffi's trampolines. This feature is implemented only on x86_32 and x86_64. The assembly sequences used here were originally obtained from PaX source code. Signed-off-by: Salvatore Mesoraca --- security/sara/Kconfig | 17 ++++ security/sara/include/trampolines.h | 171 ++++++++++++++++++++++++++++++++++++ security/sara/wxprot.c | 140 +++++++++++++++++++++++++++++ 3 files changed, 328 insertions(+) create mode 100644 security/sara/include/trampolines.h diff --git a/security/sara/Kconfig b/security/sara/Kconfig index 6c74069..f406805 100644 --- a/security/sara/Kconfig +++ b/security/sara/Kconfig @@ -96,6 +96,23 @@ choice Documentation/security/SARA.rst. endchoice +config SECURITY_SARA_WXPROT_EMUTRAMP + bool "Enable emulation for some types of trampolines" + depends on SECURITY_SARA_WXPROT + depends on X86 + default y + help + Some programs and libraries need to execute special small code + snippets from non-executable memory pages. + Most notable examples are the GCC and libffi trampolines. + This features make it possible to execute those trampolines even + if they reside in non-executable memory pages. + This features need to be enabled on a per-executable basis + via user-space utilities. + See Documentation/security/SARA.rst. for further information. + + If unsure, answer y. + config SECURITY_SARA_WXPROT_DISABLED bool "WX protection will be disabled at boot." depends on SECURITY_SARA_WXPROT diff --git a/security/sara/include/trampolines.h b/security/sara/include/trampolines.h new file mode 100644 index 0000000..eab0a85 --- /dev/null +++ b/security/sara/include/trampolines.h @@ -0,0 +1,171 @@ +/* + * S.A.R.A. Linux Security Module + * + * Copyright (C) 2017 Salvatore Mesoraca + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2, as + * published by the Free Software Foundation. + * + * Assembly sequences used here were copied from + * PaX patch by PaX Team + * + */ + +#ifndef __SARA_TRAMPOLINES_H +#define __SARA_TRAMPOLINES_H +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP + + +/* x86_32 */ + + +struct libffi_trampoline_x86_32 { + unsigned char mov; + unsigned int addr1; + unsigned char jmp; + unsigned int addr2; +} __packed; + +struct gcc_trampoline_x86_32_type1 { + unsigned char mov1; + unsigned int addr1; + unsigned char mov2; + unsigned int addr2; + unsigned short jmp; +} __packed; + +struct gcc_trampoline_x86_32_type2 { + unsigned char mov; + unsigned int addr1; + unsigned char jmp; + unsigned int addr2; +} __packed; + +union trampolines_x86_32 { + struct libffi_trampoline_x86_32 lf; + struct gcc_trampoline_x86_32_type1 g1; + struct gcc_trampoline_x86_32_type2 g2; +}; + +#define is_valid_libffi_trampoline_x86_32(UNION) \ + (UNION.lf.mov == 0xB8 && \ + UNION.lf.jmp == 0xE9) + +#define emulate_libffi_trampoline_x86_32(UNION, REGS) do { \ + (REGS)->ax = UNION.lf.addr1; \ + (REGS)->ip = (unsigned int) ((REGS)->ip + \ + UNION.lf.addr2 + \ + sizeof(UNION.lf)); \ +} while (0) + +#define is_valid_gcc_trampoline_x86_32_type1(UNION, REGS) \ + (UNION.g1.mov1 == 0xB9 && \ + UNION.g1.mov2 == 0xB8 && \ + UNION.g1.jmp == 0xE0FF && \ + REGS->ip > REGS->sp) + +#define emulate_gcc_trampoline_x86_32_type1(UNION, REGS) do { \ + (REGS)->cx = UNION.g1.addr1; \ + (REGS)->ax = UNION.g1.addr2; \ + (REGS)->ip = UNION.g1.addr2; \ +} while (0) + +#define is_valid_gcc_trampoline_x86_32_type2(UNION, REGS) \ + (UNION.g2.mov == 0xB9 && \ + UNION.g2.jmp == 0xE9 && \ + REGS->ip > REGS->sp) + +#define emulate_gcc_trampoline_x86_32_type2(UNION, REGS) do { \ + (REGS)->cx = UNION.g2.addr1; \ + (REGS)->ip = (unsigned int) ((REGS)->ip + \ + UNION.g2.addr2 + \ + sizeof(UNION.g2)); \ +} while (0) + + + +#ifdef CONFIG_X86_64 + +struct libffi_trampoline_x86_64 { + unsigned short mov1; + unsigned long addr1; + unsigned short mov2; + unsigned long addr2; + unsigned char stcclc; + unsigned short jmp1; + unsigned char jmp2; +} __packed; + +struct gcc_trampoline_x86_64_type1 { + unsigned short mov1; + unsigned long addr1; + unsigned short mov2; + unsigned long addr2; + unsigned short jmp1; + unsigned char jmp2; +} __packed; + +struct gcc_trampoline_x86_64_type2 { + unsigned short mov1; + unsigned int addr1; + unsigned short mov2; + unsigned long addr2; + unsigned short jmp1; + unsigned char jmp2; +} __packed; + +union trampolines_x86_64 { + struct libffi_trampoline_x86_64 lf; + struct gcc_trampoline_x86_64_type1 g1; + struct gcc_trampoline_x86_64_type2 g2; +}; + +#define is_valid_libffi_trampoline_x86_64(UNION) \ + (UNION.lf.mov1 == 0xBB49 && \ + UNION.lf.mov2 == 0xBA49 && \ + (UNION.lf.stcclc == 0xF8 || \ + UNION.lf.stcclc == 0xF9) && \ + UNION.lf.jmp1 == 0xFF49 && \ + UNION.lf.jmp2 == 0xE3) + +#define emulate_libffi_trampoline_x86_64(UNION, REGS) do { \ + (REGS)->r11 = UNION.lf.addr1; \ + (REGS)->r10 = UNION.lf.addr2; \ + (REGS)->ip = UNION.lf.addr1; \ + if (UNION.lf.stcclc == 0xF8) \ + (REGS)->flags &= ~X86_EFLAGS_CF; \ + else \ + (REGS)->flags |= X86_EFLAGS_CF; \ +} while (0) + +#define is_valid_gcc_trampoline_x86_64_type1(UNION, REGS) \ + (UNION.g1.mov1 == 0xBB49 && \ + UNION.g1.mov2 == 0xBA49 && \ + UNION.g1.jmp1 == 0xFF49 && \ + UNION.g1.jmp2 == 0xE3 && \ + REGS->ip > REGS->sp) + +#define emulate_gcc_trampoline_x86_64_type1(UNION, REGS) do { \ + (REGS)->r11 = UNION.g1.addr1; \ + (REGS)->r10 = UNION.g1.addr2; \ + (REGS)->ip = UNION.g1.addr1; \ +} while (0) + +#define is_valid_gcc_trampoline_x86_64_type2(UNION, REGS) \ + (UNION.g2.mov1 == 0xBB41 && \ + UNION.g2.mov2 == 0xBA49 && \ + UNION.g2.jmp1 == 0xFF49 && \ + UNION.g2.jmp2 == 0xE3 && \ + REGS->ip > REGS->sp) + +#define emulate_gcc_trampoline_x86_64_type2(UNION, REGS) do { \ + (REGS)->r11 = UNION.g2.addr1; \ + (REGS)->r10 = UNION.g2.addr2; \ + (REGS)->ip = UNION.g2.addr1; \ +} while (0) + +#endif /* CONFIG_X86_64 */ + +#endif /* CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP */ +#endif /* __SARA_TRAMPOLINES_H */ diff --git a/security/sara/wxprot.c b/security/sara/wxprot.c index f9233a5..38c86be 100644 --- a/security/sara/wxprot.c +++ b/security/sara/wxprot.c @@ -22,6 +22,11 @@ #include #include +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP +#include +#include "include/trampolines.h" +#endif + #include "include/sara.h" #include "include/sara_data.h" #include "include/utils.h" @@ -37,6 +42,7 @@ #define SARA_WXP_COMPLAIN 0x0010 #define SARA_WXP_VERBOSE 0x0020 #define SARA_WXP_MMAP 0x0040 +#define SARA_WXP_EMUTRAMP 0x0100 #define SARA_WXP_TRANSFER 0x0200 #define SARA_WXP_NONE 0x0000 #define SARA_WXP_MPROTECT (SARA_WXP_HEAP | \ @@ -47,7 +53,12 @@ SARA_WXP_WXORX | \ SARA_WXP_COMPLAIN | \ SARA_WXP_VERBOSE) +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP +#define SARA_WXP_ALL (__SARA_WXP_ALL | \ + SARA_WXP_EMUTRAMP) +#else /* CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP */ #define SARA_WXP_ALL __SARA_WXP_ALL +#endif /* CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP */ struct wxprot_rule { char *path; @@ -72,7 +83,11 @@ struct wxprot_config_container { static u16 default_flags __ro_after_init = CONFIG_SECURITY_SARA_WXPROT_DEFAULT_FLAGS; +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP +static const bool wxprot_emutramp = true; +#else static const bool wxprot_emutramp; +#endif static void pr_wxp(char *msg) { @@ -97,6 +112,9 @@ static bool are_flags_valid(u16 flags) SARA_WXP_WXORX | SARA_WXP_MMAP)))) return false; + if (unlikely(flags & SARA_WXP_EMUTRAMP && + ((flags & SARA_WXP_MPROTECT) != SARA_WXP_MPROTECT))) + return false; return true; } @@ -366,10 +384,132 @@ static int sara_file_mprotect(struct vm_area_struct *vma, return 0; } +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP +#define PF_PROT (1 << 0) +#define PF_USER (1 << 2) +#define PF_INSTR (1 << 4) +static int sara_pagefault_handler_x86_32(struct pt_regs *regs); +static int sara_pagefault_handler_x86_64(struct pt_regs *regs); +static int sara_pagefault_handler_x86(struct pt_regs *regs, + unsigned long error_code, + unsigned long address) +{ + int ret = 0; + + if (!sara_enabled || !wxprot_enabled || + !(error_code & PF_USER) || + !(error_code & PF_INSTR) || + !(error_code & PF_PROT) || + !(get_current_sara_wxp_flags() & SARA_WXP_EMUTRAMP)) + return 0; + + local_irq_enable(); + might_sleep(); + might_fault(); + +#ifdef CONFIG_X86_32 + ret = sara_pagefault_handler_x86_32(regs); +#else + if (regs->cs == __USER32_CS || + regs->cs & (1<<2)) { + if (!(address >> 32)) /* K8 erratum #100 */ + ret = sara_pagefault_handler_x86_32(regs); + } else + ret = sara_pagefault_handler_x86_64(regs); +#endif + + return ret; +} + +static int sara_pagefault_handler_x86_32(struct pt_regs *regs) +{ + int ret; + void __user *ip = (void __user *) regs->ip; + union trampolines_x86_32 t; + + BUILD_BUG_ON(sizeof(t.lf) > sizeof(t.g1)); + BUILD_BUG_ON(sizeof(t.g2) > sizeof(t.lf)); + + ret = copy_from_user(&t, ip, sizeof(t.g1)); + if (ret) + ret = copy_from_user(&t, ip, sizeof(t.lf)); + if (ret) + ret = copy_from_user(&t, ip, sizeof(t.g2)); + if (ret) + return 0; + + if (is_valid_gcc_trampoline_x86_32_type1(t, regs)) { + pr_debug("Trampoline: gcc1 x86_32.\n"); + emulate_gcc_trampoline_x86_32_type1(t, regs); + return 1; + } else if (is_valid_libffi_trampoline_x86_32(t)) { + pr_debug("Trampoline: libffi x86_32.\n"); + emulate_libffi_trampoline_x86_32(t, regs); + return 1; + } else if (is_valid_gcc_trampoline_x86_32_type2(t, regs)) { + pr_debug("Trampoline: gcc2 x86_32.\n"); + emulate_gcc_trampoline_x86_32_type2(t, regs); + return 1; + } + + pr_debug("Not a trampoline (x86_32).\n"); + + return 0; +} + +#ifdef CONFIG_X86_64 +static int sara_pagefault_handler_x86_64(struct pt_regs *regs) +{ + int ret; + void __user *ip = (void __user *) regs->ip; + union trampolines_x86_64 t; + + BUILD_BUG_ON(sizeof(t.g1) > sizeof(t.lf)); + BUILD_BUG_ON(sizeof(t.g2) > sizeof(t.g1)); + + ret = copy_from_user(&t, ip, sizeof(t.lf)); + if (ret) + ret = copy_from_user(&t, ip, sizeof(t.g1)); + if (ret) + ret = copy_from_user(&t, ip, sizeof(t.g2)); + if (ret) + return 0; + + if (is_valid_libffi_trampoline_x86_64(t)) { + pr_debug("Trampoline: libffi x86_64.\n"); + emulate_libffi_trampoline_x86_64(t, regs); + return 1; + } else if (is_valid_gcc_trampoline_x86_64_type1(t, regs)) { + pr_debug("Trampoline: gcc1 x86_64.\n"); + emulate_gcc_trampoline_x86_64_type1(t, regs); + return 1; + } else if (is_valid_gcc_trampoline_x86_64_type2(t, regs)) { + pr_debug("Trampoline: gcc2 x86_64.\n"); + emulate_gcc_trampoline_x86_64_type2(t, regs); + return 1; + } + + pr_debug("Not a trampoline (x86_64).\n"); + + return 0; + +} +#else /* CONFIG_X86_64 */ +static inline int sara_pagefault_handler_x86_64(struct pt_regs *regs) +{ + return 0; +} +#endif /* CONFIG_X86_64 */ + +#endif /* CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP */ + static struct security_hook_list wxprot_hooks[] __ro_after_init = { LSM_HOOK_INIT(bprm_set_creds, sara_bprm_set_creds), LSM_HOOK_INIT(check_vmflags, sara_check_vmflags), LSM_HOOK_INIT(file_mprotect, sara_file_mprotect), +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP + LSM_HOOK_INIT(pagefault_handler_x86, sara_pagefault_handler_x86), +#endif }; struct binary_config_header {