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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 353B1C10F11 for ; Wed, 24 Apr 2019 20:51:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0C3C0218FE for ; Wed, 24 Apr 2019 20:51:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733180AbfDXUv2 (ORCPT ); Wed, 24 Apr 2019 16:51:28 -0400 Received: from foss.arm.com ([217.140.101.70]:55236 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728083AbfDXUv2 (ORCPT ); Wed, 24 Apr 2019 16:51:28 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DB241A78; Wed, 24 Apr 2019 13:51:27 -0700 (PDT) Received: from brain-police (usa-sjc-mx-foss1.foss.arm.com [217.140.101.70]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 585253F557; Wed, 24 Apr 2019 13:51:24 -0700 (PDT) Date: Wed, 24 Apr 2019 21:51:17 +0100 From: Will Deacon To: Kees Cook Cc: Andrew Morton , Hector Marco-Gisbert , Marc Gonzalez , Jason Gunthorpe , x86@kernel.org, Thomas Gleixner , Andy Lutomirski , Stephen Rothwell , Catalin Marinas , Mark Rutland , Arnd Bergmann , Linux ARM , Kernel Hardening , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] binfmt_elf: Update READ_IMPLIES_EXEC logic for modern CPUs Message-ID: <20190424205117.GA5291@brain-police> References: <20190424203408.GA11386@beast> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190424203408.GA11386@beast> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 24, 2019 at 01:34:08PM -0700, Kees Cook wrote: > The READ_IMPLIES_EXEC work-around was designed for old CPUs lacking NX > (to have the visible permission flags on memory regions reflect reality: > they are all executable), and for old toolchains that lacked the ELF > PT_GNU_STACK marking (under the assumption that toolchains that couldn't > even specify memory protection flags may have it wrong for all memory > regions). > > This logic is sensible, 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. This is not a reasonable assumption > for CPUs that have had NX support from the start (or very close to > the start). This confusion has led to situations where modern 64-bit > 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].) > > To fix this, elf_read_implies_exec() is adjusted on arm64 (where NX has > always existed and toolchains have implemented PT_GNU_STACK for a while), > and x86 is adjusted to handle this combination of possible outcomes: > > CPU: | lacks NX | has NX, ia32 | has NX, x86_64 | > ELF: | | | | > ------------------------------|------------------|------------------| > missing GNU_STACK | needs RIE | needs RIE | no RIE | > GNU_STACK == RWX | needs RIE | no RIE: stack X | no RIE: stack X | > GNU_STACK == RW | needs RIE | no RIE: stack NX | no RIE: stack NX | > > This has the effect of making binfmt_elf's EXSTACK_DEFAULT actually take > on the correct architecture default of being non-executable on arm64 and > x86_64, and being executable on ia32. > > [1] https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com > > Suggested-by: Hector Marco-Gisbert > Signed-off-by: Kees Cook > --- > v2: adjust arm64 to avoid is_compat_task() (marc.w.gonzalez) > --- > arch/arm64/include/asm/elf.h | 8 +++++++- > arch/x86/include/asm/elf.h | 24 +++++++++++++++++++++--- > 2 files changed, 28 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h > index 6adc1a90e7e6..f1bb4b388b8f 100644 > --- a/arch/arm64/include/asm/elf.h > +++ b/arch/arm64/include/asm/elf.h > @@ -107,7 +107,13 @@ > */ > #define elf_check_arch(x) ((x)->e_machine == EM_AARCH64) > > -#define elf_read_implies_exec(ex,stk) (stk != EXSTACK_DISABLE_X) > +/* > + * 64-bit processes should not automatically gain READ_IMPLIES_EXEC. Only > + * 32-bit processes without PT_GNU_STACK should trigger READ_IMPLIES_EXEC > + * out of an abundance of caution against ancient toolchains not knowing > + * how to mark memory protection flags correctly. > + */ > +#define compat_elf_read_implies_exec(ex, stk) (stk == EXSTACK_DEFAULT) Don't you need to hack fs/compat_binfmt_elf.c to pick this up, or am I missing some trick? Should just be something like below. Will --->8 diff --git a/fs/compat_binfmt_elf.c b/fs/compat_binfmt_elf.c index 15f6e96b3bd9..694bc3ee77eb 100644 --- a/fs/compat_binfmt_elf.c +++ b/fs/compat_binfmt_elf.c @@ -116,6 +116,11 @@ #define arch_setup_additional_pages compat_arch_setup_additional_pages #endif +#ifdef compat_elf_read_implies_exec +#undef elf_read_implies_exec +#define elf_read_implies_exec compat_elf_read_implies_exec +#endif + /* * Rename a few of the symbols that binfmt_elf.c will define. * These are all local so the names don't really matter, but it