From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5BB12C43331 for ; Fri, 27 Mar 2020 06:48:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2830520714 for ; Fri, 27 Mar 2020 06:48:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="JROchnuo" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727791AbgC0Gsf (ORCPT ); Fri, 27 Mar 2020 02:48:35 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:45535 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727720AbgC0Gsb (ORCPT ); Fri, 27 Mar 2020 02:48:31 -0400 Received: by mail-pg1-f195.google.com with SMTP id o26so4128872pgc.12 for ; Thu, 26 Mar 2020 23:48:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=9LO2LzsxD2r9Xv+srqALdfcgB8lxU6x5iZM1oUedN0w=; b=JROchnuoQhF2R/Mx5z01GK7uJjfXpDKE0LvGoYpHwUfQ1LM+YDoX9iNWypkcK6H8ga Y52O13oWS8BcrW5QYSCbprsyCVbOVMXojnxUDi6FH0Bi6Y3Zq7JyhA+8mCT1Z1cEBymy PJxdNR/1VyMhsLDwzYotBhML4MtN9DLzspX50= 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:mime-version:content-transfer-encoding; bh=9LO2LzsxD2r9Xv+srqALdfcgB8lxU6x5iZM1oUedN0w=; b=flrfkrPgCkwhZcGecpXwypCcGgSnTjZvXVKE2pKrvoEtrdnUanvNnc9EM+9OVl5gcl yLKrKmJQp/L+dHUOVJ/3kKBMSRwqKkQ9Uv6hBn5qFpNy0FTNaye7SRqecriI0JybV5lE qCl5FYD5ct8uNrmqUYiCUNa0UCky3Hw51mvg4mI1wKsgDH/34fJCoCDKJmVsKaITy403 S86ROnrvUnzMhX+KHNsRpyPK93dzlIhqxelHD9Xa/mIhs6gj0cZEWqi+Wv2gAxY11tTb CI5quavqH2VIshHiba3Og82Hrczqz9X7oQ6n6d6peWbbe+0kj83vsK6Nr4DZOOS1Unlb G0hA== X-Gm-Message-State: ANhLgQ2sfWaSoVkODZRJc1UFoHtqBwFr5swqvtgjmMjvvi4pJIvoqcxp dMJaLgpowV152ZvB4ZKq80WW4w== X-Google-Smtp-Source: ADFU+vuA1LFfImtyYtbDmLUlKIzpXJoC5cD77qNyfHDvBSDw6ezHZbSgFf8tN7H3qURKXYRhUoj5iA== X-Received: by 2002:a62:2c8c:: with SMTP id s134mr13352706pfs.253.1585291709337; Thu, 26 Mar 2020 23:48:29 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id n22sm2975913pjq.36.2020.03.26.23.48.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2020 23:48:27 -0700 (PDT) From: Kees Cook To: Borislav Petkov Cc: Kees Cook , Hector Marco-Gisbert , Jason Gunthorpe , Catalin Marinas , Jason Gunthorpe , Russell King , Will Deacon , Jann Horn , x86@kernel.org, linux-arm-kernel@lists.infradead.org, kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org Subject: [PATCH v5 5/6] arm32/64, elf: Split READ_IMPLIES_EXEC from executable PT_GNU_STACK Date: Thu, 26 Mar 2020 23:48:19 -0700 Message-Id: <20200327064820.12602-6-keescook@chromium.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200327064820.12602-1-keescook@chromium.org> References: <20200327064820.12602-1-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The READ_IMPLIES_EXEC work-around was designed for old toolchains that lacked the ELF PT_GNU_STACK marking under the assumption that toolchains that couldn't specify executable permission flags for the stack may not know how to do it correctly for any memory region. This logic is sensible for having ancient binaries coexist in a system with possibly NX memory, but was implemented in a way that equated having a PT_GNU_STACK marked executable as being as "broken" as lacking the PT_GNU_STACK marking entirely. Things like unmarked assembly and stack trampolines may cause PT_GNU_STACK to need an executable bit, but they do not imply all mappings must be executable. This confusion has led to situations where modern programs with explicitly marked executable stack are forced into the READ_IMPLIES_EXEC state when no such thing is needed. (And leads to unexpected failures when mmap()ing regions of device driver memory that wish to disallow VM_EXEC[1].) In looking for other reasons for the READ_IMPLIES_EXEC behavior, Jann Horn noted that glibc thread stacks have always been marked RWX (until 2003 when they started tracking the PT_GNU_STACK flag instead[2]). And musl doesn't support executable stacks at all[3]. As such, no breakage for multithreaded applications is expected from this change. This changes arm32 and arm64 compat together, to keep behavior the same. [1] https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com [2] https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=54ee14b3882 [3] https://lkml.kernel.org/r/20190423192534.GN23599@brightrain.aerifal.cx Suggested-by: Hector Marco-Gisbert Signed-off-by: Kees Cook Reviewed-by: Jason Gunthorpe Reviewed-by: Catalin Marinas --- arch/arm/kernel/elf.c | 5 +++-- arch/arm64/include/asm/elf.h | 5 +++-- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/arch/arm/kernel/elf.c b/arch/arm/kernel/elf.c index 5ccd4aced6cc..254ab7138c85 100644 --- a/arch/arm/kernel/elf.c +++ b/arch/arm/kernel/elf.c @@ -87,12 +87,13 @@ EXPORT_SYMBOL(elf_set_personality); * ELF:              |            |           | * ---------------------|------------|------------| * missing PT_GNU_STACK | exec-all   | exec-all  | - * PT_GNU_STACK == RWX  | exec-all   | exec-all  | + * PT_GNU_STACK == RWX  | exec-all   | exec-stack | * PT_GNU_STACK == RW   | exec-all  | exec-none | * * exec-all : all PROT_READ user mappings are executable, except when * backed by files on a noexec-filesystem. * exec-none : only PROT_EXEC user mappings are executable. + * exec-stack: only the stack and PROT_EXEC user mappings are executable. * * *this column has no architectural effect: NX markings are ignored by * hardware, but may have behavioral effects when "wants X" collides with @@ -102,7 +103,7 @@ EXPORT_SYMBOL(elf_set_personality); */ int arm_elf_read_implies_exec(int executable_stack) { - if (executable_stack != EXSTACK_DISABLE_X) + if (executable_stack == EXSTACK_DEFAULT) return 1; if (cpu_architecture() < CPU_ARCH_ARMv6) return 1; diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h index 986ecf41fc0f..0074e9fd6431 100644 --- a/arch/arm64/include/asm/elf.h +++ b/arch/arm64/include/asm/elf.h @@ -106,17 +106,18 @@ * ELF:              |            |            | * ---------------------|------------|------------| * missing PT_GNU_STACK | exec-all   | exec-all   | - * PT_GNU_STACK == RWX  | exec-all   | exec-all   | + * PT_GNU_STACK == RWX  | exec-stack | exec-stack | * PT_GNU_STACK == RW   | exec-none | exec-none | * * exec-all : all PROT_READ user mappings are executable, except when * backed by files on a noexec-filesystem. * exec-none : only PROT_EXEC user mappings are executable. + * exec-stack: only the stack and PROT_EXEC user mappings are executable. * * *all arm64 CPUs support NX, so there is no "lacks NX" column. * */ -#define elf_read_implies_exec(ex,stk) (stk != EXSTACK_DISABLE_X) +#define elf_read_implies_exec(ex, stk) (stk == EXSTACK_DEFAULT) #define CORE_DUMP_USE_REGSET #define ELF_EXEC_PAGESIZE PAGE_SIZE -- 2.20.1