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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 47765C48BCD for ; Wed, 9 Jun 2021 15:18:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2C38A611CC for ; Wed, 9 Jun 2021 15:18:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233556AbhFIPUr (ORCPT ); Wed, 9 Jun 2021 11:20:47 -0400 Received: from foss.arm.com ([217.140.110.172]:34286 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239442AbhFIPUK (ORCPT ); Wed, 9 Jun 2021 11:20:10 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4C4DBD6E; Wed, 9 Jun 2021 08:18:15 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F01B63F73D; Wed, 9 Jun 2021 08:18:13 -0700 (PDT) Date: Wed, 9 Jun 2021 16:17:13 +0100 From: Dave Martin To: Mark Brown Cc: Catalin Marinas , Will Deacon , Szabolcs Nagy , Jeremy Linton , "H . J . Lu" , Yu-cheng Yu , linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, libc-alpha@sourceware.org Subject: Re: [PATCH v2 2/3] arm64: Enable BTI for main executable as well as the interpreter Message-ID: <20210609151713.GL4187@arm.com> References: <20210604112450.13344-1-broonie@kernel.org> <20210604112450.13344-3-broonie@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210604112450.13344-3-broonie@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote: > Currently for dynamically linked ELF executables we only enable BTI for > the interpreter, expecting the interpreter to do this for the main > executable. This is a bit inconsistent since we do map main executable and > is causing issues with systemd's MemoryDenyWriteExecute feature which is > implemented using a seccomp filter which prevents setting PROT_EXEC on > already mapped memory and lacks the context to be able to detect that > memory is already mapped with PROT_EXEC. > > Resolve this by checking the BTI property for the main executable and > enabling BTI if it is present when doing the initial mapping. This does > mean that we may get more code with BTI enabled if running on a system > without BTI support in the dynamic linker, this is expected to be a safe > configuration and testing seems to confirm that. It also reduces the > flexibility userspace has to disable BTI but it is expected that for cases > where there are problems which require BTI to be disabled it is more likely > that it will need to be disabled on a system level. > > Signed-off-by: Mark Brown > Reviewed-by: Dave Martin > --- > arch/arm64/include/asm/elf.h | 14 ++++++++++---- > arch/arm64/kernel/process.c | 18 ++++++------------ > 2 files changed, 16 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h > index a488a1329b16..9f86dbce2680 100644 > --- a/arch/arm64/include/asm/elf.h > +++ b/arch/arm64/include/asm/elf.h > @@ -253,7 +253,8 @@ struct arch_elf_state { > int flags; > }; > > -#define ARM64_ELF_BTI (1 << 0) > +#define ARM64_ELF_INTERP_BTI (1 << 0) > +#define ARM64_ELF_EXEC_BTI (1 << 1) > > #define INIT_ARCH_ELF_STATE { \ > .flags = 0, \ > @@ -274,9 +275,14 @@ static inline int arch_parse_elf_property(u32 type, const void *data, > if (datasz != sizeof(*p)) > return -ENOEXEC; > > - if (system_supports_bti() && has_interp == is_interp && > - (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) > - arch->flags |= ARM64_ELF_BTI; > + if (system_supports_bti() && > + (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) { > + if (is_interp) { > + arch->flags |= ARM64_ELF_INTERP_BTI; > + } else { > + arch->flags |= ARM64_ELF_EXEC_BTI; > + } Nit: surplus curlies? (coding-style.rst does actually say to drop them when all branches of an if are single-statement one-liners -- I had presumed I was just being pedantic...) > + } > } > > return 0; > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index b4bb67f17a2c..f7fff4a4c99f 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -744,19 +744,13 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void) > int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, > bool has_interp, bool is_interp) > { > - /* > - * For dynamically linked executables the interpreter is > - * responsible for setting PROT_BTI on everything except > - * itself. > - */ > - if (is_interp != has_interp) > - return prot; > + if (prot & PROT_EXEC) { > + if (state->flags & ARM64_ELF_INTERP_BTI && is_interp) > + prot |= PROT_BTI; > > - if (!(state->flags & ARM64_ELF_BTI)) > - return prot; > - > - if (prot & PROT_EXEC) > - prot |= PROT_BTI; > + if (state->flags & ARM64_ELF_EXEC_BTI && !is_interp) > + prot |= PROT_BTI; > + } Is it worth adding () around the bitwise-& expressions? I'm always a little uneasy about the operator precedence of binary &, although without looking it up I think you're correct. Also, due to symmetry between arch_elf_adjust_prot() and arch_parse_elf_properties() here, could we have something like static inline int arm64_elf_bti_flag(bool is_interp) { if (is_interp) return ARM64_ELF_INTERP_BTI; else return ARM64_ELF_EXEC_BTI; } and then have code like if (state->flags & arm64_elf_bti_flag(is_interp)) prot |= PROT_BTI; here (with analogous code in arch_elf_adjust_prot()). Feel free to adopt if this appeals to you, otherwise I'm also fine with your version.) Either way, these comments are all pretty much cosmetic, and my Reviewed-by stands. Cheers ---Dave