From patchwork Tue Feb 25 05:13:03 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 11402511 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 6189614BC for ; Tue, 25 Feb 2020 05:13:41 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id BD82124683 for ; Tue, 25 Feb 2020 05:13:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="cYoKF8t4" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BD82124683 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-17899-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 7435 invoked by uid 550); 25 Feb 2020 05:13:26 -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 7359 invoked from network); 25 Feb 2020 05:13:25 -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=xtFhZmUGg25ckYL+Nj/gQvxOaU7nm2sSSfbBJDheRi8=; b=cYoKF8t4ZKo9npvA7QP9XflS8FuxXhlRBK6xAEmgOI8SDB3qsyrUamZa+IZxIQeHEl hic9kuq1J+X/MvlwBhVTB5UE5AibQJRe0f4VCVIgnILVgGTTdcdSXyNKEVybEbiEpVNI KIqP3vXsNrYdk9Oin86blNR1kimWfFn+e1wBs= 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=xtFhZmUGg25ckYL+Nj/gQvxOaU7nm2sSSfbBJDheRi8=; b=TBGKJi4pKBDf3sfZH5DYR4ehjHULMrTeNH7GowodgMDzFyqC/pnd0LlNb7hQX97hiA c4ABLCf4rqp+wdmglJRwVo7OIE+Kbs96RJWC8vvPvH8s8miaAaCnuuTf0ClUCfgQwdP7 2K81I+bLVGd/UDTpuX9xgTb741+pdpd2Tk1mKKq0pRFF/sAi7c/VOmnoBwwJnUEYz8Vp FfC6dt4FXF6Z/guL0xgr5cgXAAoB1p6slDmWS1OX3n9qM2Yp/v+VUMl0CW+1YJ03aE/w dGtNt1N44+riN2HGCqTPFWNk9vpUvQH2vx/HqsLgRHvvINbS3hjaz9ANdd3UlIsmyG19 Jz9Q== X-Gm-Message-State: APjAAAUX0A2/lOxcHkdl360dKSU6alnosFUKEMmJRGGIHEOCRa6p6mta /fwOhiD1ZrkqJdoWyb+rIB5uiA== X-Google-Smtp-Source: APXvYqwODtU4FUfT5WxcMcB9c17YZwUi3dfzZeLH4lgWsLytNLFPaPcQmbSyyLc8Ik4xhECJhuDusg== X-Received: by 2002:a63:d40d:: with SMTP id a13mr57785788pgh.9.1582607593779; Mon, 24 Feb 2020 21:13:13 -0800 (PST) From: Kees Cook To: Borislav Petkov Cc: Kees Cook , Hector Marco-Gisbert , Jason Gunthorpe , Jason Gunthorpe , Catalin Marinas , 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 2/6] x86/elf: Split READ_IMPLIES_EXEC from executable GNU_STACK Date: Mon, 24 Feb 2020 21:13:03 -0800 Message-Id: <20200225051307.6401-3-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. [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 --- arch/x86/include/asm/elf.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index 733f69c2b053..a7035065377c 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -288,12 +288,13 @@ extern u32 elf_hwcap2; * ELF:              |            |                  |                | * -------------------------------|------------------|----------------| * missing GNU_STACK | exec-all   | exec-all         | exec-all       | - * GNU_STACK == RWX  | exec-all   | exec-all         | exec-all       | + * GNU_STACK == RWX  | exec-stack | exec-stack       | exec-stack     | * GNU_STACK == RW   | exec-none  | 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. * * *this column has no architectural effect: NX markings are ignored by * hardware, but may have behavioral effects when "wants X" collides with @@ -302,7 +303,7 @@ extern u32 elf_hwcap2; * */ #define elf_read_implies_exec(ex, executable_stack) \ - (executable_stack != EXSTACK_DISABLE_X) + (executable_stack == EXSTACK_DEFAULT) struct task_struct;