From patchwork Mon Feb 10 19:30:42 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 11373997 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 4B20F109A for ; Mon, 10 Feb 2020 19:31:14 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id A72E320838 for ; Mon, 10 Feb 2020 19:31:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="BH7Ud+6o" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A72E320838 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-17761-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 11810 invoked by uid 550); 10 Feb 2020 19:31:11 -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 11772 invoked from network); 10 Feb 2020 19:31:11 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=7BxkgltGo3ZM9ZY7Grbu2bcNcn+pz+GDYrC11ZXD2ME=; b=BH7Ud+6oFq+7OoIlLBbbMvTBHC4x6G8tRrT4wZScXP2/0BYU5O8AgFFlezKTTpQYMV fmiGPa9peDfUrdZdj+9xqS9t7Ua491OZzp4RIZLg3Giw7fhPm1FvIbwzaS9NqQojoCMv 95B0WHndyisDS9V4XA1xkVEyzq6091EvwvmT4= 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:mime-version :content-transfer-encoding; bh=7BxkgltGo3ZM9ZY7Grbu2bcNcn+pz+GDYrC11ZXD2ME=; b=CbNYhsABHV/WrJzIeea0P19VXfgQ9I1J938WhraA/9Y05Bqkq3pBDe5Is5NvaCvlqq bfdD5ir8NyzgGSQ5MImWyRierqj05cPuXTkbR1Dl5trw2k6HlOlNgEH9En0W6kY1IFWk YeHs02nC9ayRHsmnytxRqlhYcKmZSEMs7dunAF4xZVtYCF6E6tlSxfFVIAJQ7h53exRN VeVj6kI+5hXVXwkQHHzUI1kAFEfsGs9hJGJWn7zeoaBwwFGRlP/45+aZZvWop9Enb280 RPTVMwSKxFp/XgGMHduYlpPx00FA31hr7jHcJRbtpo4yU4h1slY7ixsLFXBd+Ik6jfEy 5CDQ== X-Gm-Message-State: APjAAAUR/UmkGgMu+eBYFHCBM7ye1SRcecBp9OuvScL1nhJSfE2Pc+hG N6oGDyR8xm7h3oyFajwU+Cl2QQ== X-Google-Smtp-Source: APXvYqzUOzBqZYnuPC5ne0YCYJNkucq+pHiY9zdgP+OtGzcaHv4jX1sC238odS+TkQrM/uoVlWRNEA== X-Received: by 2002:aca:5a04:: with SMTP id o4mr405786oib.71.1581363059273; Mon, 10 Feb 2020 11:30:59 -0800 (PST) From: Kees Cook To: Ingo Molnar Cc: Kees Cook , Hector Marco-Gisbert , Catalin Marinas , Will Deacon , Jason Gunthorpe , Jann Horn , Russell King , x86@kernel.org, kernel-hardening@lists.openwall.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v3 0/7] binfmt_elf: Update READ_IMPLIES_EXEC logic for modern CPUs Date: Mon, 10 Feb 2020 11:30:42 -0800 Message-Id: <20200210193049.64362-1-keescook@chromium.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Hi, This is a refresh of my earlier attempt to fix READ_IMPLIES_EXEC. I think it incorporates the feedback from v2, and I've now added a selftest. This series is for x86, arm, and arm64; I'd like it to go via -tip, though, just to keep this change together with the selftest. To that end, I'd like to collect Acks from the respective architecture maintainers. (Note that most other architectures don't suffer from this problem. e.g. powerpc's behavior appears to already be correct. MIPS may need adjusting but the history of CPU features and toolchain behavior is very unclear to me.) Repeating the commit log from later in the series: 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 -Kees v3: - split steps in to distinct patches - include arm32 and arm64/compat - add selftests to validate behavior v2: https://lore.kernel.org/lkml/20190424203408.GA11386@beast/ v1: https://lore.kernel.org/lkml/20190423181210.GA2443@beast/ Kees Cook (7): x86/elf: Add table to document READ_IMPLIES_EXEC x86/elf: Split READ_IMPLIES_EXEC from executable GNU_STACK x86/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces arm32/64, elf: Add tables to document READ_IMPLIES_EXEC arm32/64, elf: Split READ_IMPLIES_EXEC from executable GNU_STACK arm64, elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces selftests/exec: Add READ_IMPLIES_EXEC tests arch/arm/kernel/elf.c | 27 +++- arch/arm64/include/asm/elf.h | 23 +++- arch/x86/include/asm/elf.h | 22 +++- fs/compat_binfmt_elf.c | 5 + tools/testing/selftests/exec/Makefile | 42 +++++- .../selftests/exec/read_implies_exec.c | 121 ++++++++++++++++++ .../selftests/exec/strip-gnu-stack-bits.c | 34 +++++ .../testing/selftests/exec/strip-gnu-stack.c | 69 ++++++++++ 8 files changed, 336 insertions(+), 7 deletions(-) create mode 100644 tools/testing/selftests/exec/read_implies_exec.c create mode 100644 tools/testing/selftests/exec/strip-gnu-stack-bits.c create mode 100644 tools/testing/selftests/exec/strip-gnu-stack.c Reviewed-by: Jason Gunthorpe