From patchwork Tue Feb 25 05:13:06 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 11402527 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9949914E3 for ; Tue, 25 Feb 2020 05:14:23 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id CBEB22467C for ; Tue, 25 Feb 2020 05:14:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="DPDiTUn9" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CBEB22467C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-17904-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 7727 invoked by uid 550); 25 Feb 2020 05:13:32 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 7538 invoked from network); 25 Feb 2020 05:13:28 -0000 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=2lIWrB2rl2fls1DP3gLk6fTzwbihtKCjsTFZYdDbGQ4=; b=DPDiTUn9mHAJPUVeuO6O/4+ZWGT7CXMflUkvN2DOGwNzNVpUoWmOyBDAPPODhXWKny NAGKI6c4hPVF4ebdPpwklU4evW4Jv0T46fb90WvXFEfUBpzH+zSH2ffMjDvLcQk8cmtw yow7naoX3eK49OZ2mSrrxi/CmK2iPRw64SR2c= 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=2lIWrB2rl2fls1DP3gLk6fTzwbihtKCjsTFZYdDbGQ4=; b=pwJxXk/h1YFoUc0eBNbqM+4UQaDiK0z9Oacu5UH+cafHi1GWYgP6my4IcwCfgDrIxd wsAOSjMQHKCurOJAr1jfVhcEy2L0WmXgUj5P0IXDdyZsJ0Kqo6Wvux7bDWjj5Y3DA4lA Mv/UtwfNd0v4pIUaK7SrWI8qCPnDrGQME/3PsC4PSmkFCC6QMMw5crJTKjEiq9+vZxdR E+D0fUaiZ+Dhaf8kbWLxbYc/yZO7MoVYX8TFZYVoyhDoCR0++sS2+Ad0eT73++RNLbfQ YgjEDv54fQq2pa4m05mvLNQGOnNzp5YkwUJ37rmbjh1TYMqZuj8RL/bY3dVycE3ZELQZ xUAQ== X-Gm-Message-State: APjAAAXlrPzZwf+M2/UchPu1S7A7V3yEVOBfiv66SOZvq6SfclNtUPOn 5vbHd0n7WR/W6qb+wboX9NgPJQ== X-Google-Smtp-Source: APXvYqypIEhUi0EJIgMKTYt0m4YMRHeIhF58LfEi+94S8qvARJ0jimCVUlM03w63T/gtF6c3CH2Xsg== X-Received: by 2002:aa7:8101:: with SMTP id b1mr56045649pfi.105.1582607596919; Mon, 24 Feb 2020 21:13:16 -0800 (PST) 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 v4 5/6] arm32/64, elf: Split READ_IMPLIES_EXEC from executable GNU_STACK Date: Mon, 24 Feb 2020 21:13:06 -0800 Message-Id: <20200225051307.6401-6-keescook@chromium.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200225051307.6401-1-keescook@chromium.org> References: <20200225051307.6401-1-keescook@chromium.org> MIME-Version: 1.0 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 2f69cf978fe3..6965a673a141 100644 --- a/arch/arm/kernel/elf.c +++ b/arch/arm/kernel/elf.c @@ -87,12 +87,13 @@ EXPORT_SYMBOL(elf_set_personality); * ELF:              |            |           | * -------------------------------|------------| * missing GNU_STACK | exec-all   | exec-all  | - * GNU_STACK == RWX  | exec-all   | exec-all  | + * GNU_STACK == RWX  | exec-all   | exec-stack | * 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 7fc779e3f1ec..03ada29984a7 100644 --- a/arch/arm64/include/asm/elf.h +++ b/arch/arm64/include/asm/elf.h @@ -106,17 +106,18 @@ * ELF:              |            |            | * -------------------------------|------------| * missing GNU_STACK | exec-all   | exec-all   | - * GNU_STACK == RWX  | exec-all   | exec-all   | + * GNU_STACK == RWX  | exec-stack | exec-stack | * 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