From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS17314 8.43.84.0/22 X-Spam-Status: No, score=-3.7 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, PDS_RDNS_DYNAMIC_FP,RCVD_IN_DNSWL_MED,RDNS_DYNAMIC,SPF_HELO_PASS, SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (ip-8-43-85-97.sourceware.org [8.43.85.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id ACE1D1F5AE for ; Mon, 19 Jul 2021 10:07:22 +0000 (UTC) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id EC57F3861035 for ; Mon, 19 Jul 2021 10:07:21 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org EC57F3861035 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1626689242; bh=QtUoCkLzNdb8NmMevAtAjlZZElgABIKGxA7jqasblfE=; h=Date:To:Subject:References:In-Reply-To:List-Id:List-Unsubscribe: List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc: From; b=A0hiZv9xXtz4lDGCKNgdS4iNxXl5E5ABq7QYjHu4dbojoIDKmKn9uvoy2sUMNL7E4 enJMz90Btiu5DRrUv1R02MtGAgNELEDjfdODEED2KgNez0LqouLbyNVjDFRMnHPULT nWsmSOdh6skH9VZIxfjMGTnPajdvTv62glhohmxM= Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by sourceware.org (Postfix) with ESMTP id 85D7F393FC34 for ; Mon, 19 Jul 2021 10:06:26 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 85D7F393FC34 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 1DE0E6D; Mon, 19 Jul 2021 03:06:26 -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 C15763F73D; Mon, 19 Jul 2021 03:06:24 -0700 (PDT) Date: Mon, 19 Jul 2021 11:05:08 +0100 To: Mark Brown Subject: Re: [PATCH v4 2/4] arm64: Enable BTI for main executable as well as the interpreter Message-ID: <20210719100507.GU4187@arm.com> References: <20210712115259.29547-1-broonie@kernel.org> <20210712115259.29547-3-broonie@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210712115259.29547-3-broonie@kernel.org> User-Agent: Mutt/1.5.23 (2014-03-12) X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Dave Martin via Libc-alpha Reply-To: Dave Martin Cc: linux-arch@vger.kernel.org, Yu-cheng Yu , libc-alpha@sourceware.org, Szabolcs Nagy , Catalin Marinas , Jeremy Linton , Will Deacon , linux-arm-kernel@lists.infradead.org Errors-To: libc-alpha-bounces+e=80x24.org@sourceware.org Sender: "Libc-alpha" On Mon, Jul 12, 2021 at 12:52:57PM +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 > Tested-by: Jeremy Linton > --- > arch/arm64/include/asm/elf.h | 14 ++++++++++---- > arch/arm64/kernel/process.c | 23 +++++++++++------------ > 2 files changed, 21 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; > + } Can this just be arch->flags |= arm64_elf_bti_flag(is_interp); if the helper is moved to this header? > + } > } > > return 0; > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index c8989b999250..5a6c3b198bd3 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -683,21 +683,20 @@ core_initcall(tagged_addr_init); > #endif /* CONFIG_ARM64_TAGGED_ADDR_ABI */ > > #ifdef CONFIG_BINFMT_ELF > -int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, > - bool has_interp, bool is_interp) > +static inline int arm64_elf_bti_flag(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 (is_interp) > + return ARM64_ELF_INTERP_BTI; > + else > + return ARM64_ELF_EXEC_BTI; > +} > > - if (!(state->flags & ARM64_ELF_BTI)) > - return prot; > > - if (prot & PROT_EXEC) > +int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state, > + bool has_interp, bool is_interp) > +{ > + if ((prot & PROT_EXEC) && > + (state->flags & arm64_elf_bti_flag(is_interp))) Preferably with the above change (but if not, I'll live without): Reviewed-by: Dave Martin > prot |= PROT_BTI; > > return prot; > --