From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by sourceware.org (Postfix) with ESMTP id 962D53850419 for ; Thu, 10 Jun 2021 15:35:30 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 962D53850419 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 173C2106F; Thu, 10 Jun 2021 08:35:30 -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 B89CF3F719; Thu, 10 Jun 2021 08:35:28 -0700 (PDT) Date: Thu, 10 Jun 2021 16:34:28 +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: <20210610153426.GP4187@arm.com> References: <20210604112450.13344-1-broonie@kernel.org> <20210604112450.13344-3-broonie@kernel.org> <20210609151713.GL4187@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Status: No, score=-5.9 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org 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: , X-List-Received-Date: Thu, 10 Jun 2021 15:35:32 -0000 On Thu, Jun 10, 2021 at 02:19:05PM +0100, Mark Brown wrote: > On Wed, Jun 09, 2021 at 04:17:13PM +0100, Dave Martin wrote: > > On Fri, Jun 04, 2021 at 12:24:49PM +0100, Mark Brown wrote: > > > > - 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...) > > I really think this hurts readability with the nested if inside > another if with a multi-line condition. So long as there is a reason rather than it being purely an accident of editing, that's fine. (Though if the nested if can be flattened so that this becomes a non- issue, that's good too :) > > > - 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. > > Sure. I'm fairly sure the compiler would've complained about > this case if it were ambiguous, I'm vaguely surprised it didn't > already. I was vaguely surprised too -- though I didn't try to compile this myself yet. Anyway, not a huge deal. Adding a helper to generate the appropriate mask would make this issue go away in any case, but so long as you're confident this is being evaluated as intended I can take your word for it. > > Feel free to adopt if this appeals to you, otherwise I'm also fine with > > your version.) > > I'll see what I think when I get back to looking at this > properly. Ack -- again, this was just a suggestion. I can also live with your original code if you ultimately decide to stick with that. Cheers ---Dave