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=-12.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 37B4FC55178 for ; Wed, 28 Oct 2020 17:58:06 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9D8F0247F9 for ; Wed, 28 Oct 2020 17:58:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="SqYbD1CI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9D8F0247F9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=azSSA9M69X1zsIJqEaJPh9Fg0+nfiPm3az8wGkYQOTc=; b=SqYbD1CIEDQWMWzz5qKcJpgjR rPkS6w0RaCu8AFkNFcDKMPNAJWM32/eSAs7tZHrxM2KHGAFhDX9Ez4vK2BjSmsp7WVyO4orgFvsuC Gx4vjTqHtcYM0BiTYhBxYm/0c2Lpi98Cqhf4VytP+JqyVsPer37ryosNW+AQC9uo6vjvV4/WFlc/F UsSr0PL2hcEiA49zuPX1z7lxxVILL3UXjfRXKHa/4ArYCbXPzL9k85ceEzE3F/DOxnUmrRhmYY0by KdcvPl1/XPvqmGWTCJ1M+8ifRAxLrqn/jrZX/hEEsbTrAQA5qi8bTFzTw6ndoHd7KbMt1XdRxSLKw 18xOl5+ZA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXpgi-0008Sf-7W; Wed, 28 Oct 2020 17:56:44 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kXpga-0008R5-Gw for linux-arm-kernel@lists.infradead.org; Wed, 28 Oct 2020 17:56:37 +0000 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 90C27176C; Wed, 28 Oct 2020 10:56:34 -0700 (PDT) Received: from [10.57.54.223] (unknown [10.57.54.223]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 83E6D3F719; Wed, 28 Oct 2020 10:56:33 -0700 (PDT) Subject: Re: [PATCH 4/4] arm64: head: tidy up the Image header definition To: Will Deacon , Ard Biesheuvel References: <20201027073209.2897-1-ardb@kernel.org> <20201027073209.2897-5-ardb@kernel.org> <20201028141726.GE28554@willie-the-truck> From: Robin Murphy Message-ID: Date: Wed, 28 Oct 2020 17:56:32 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201028141726.GE28554@willie-the-truck> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201028_135636_679794_3D5E4626 X-CRM114-Status: GOOD ( 23.08 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, catalin.marinas@arm.com, james.morse@arm.com, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-10-28 14:17, Will Deacon wrote: > On Tue, Oct 27, 2020 at 08:32:09AM +0100, Ard Biesheuvel wrote: >> Even though support for EFI boot remains entirely optional for arm64, >> it is unlikely that we will ever be able to repurpose the image header >> fields that the EFI loader relies on, i.e., the magic NOP at offset >> 0x0 and the PE header address at offset 0x3c. >> >> So let's factor out the differences into a 'magic_nop' macro and a local >> symbol representing the PE header address, and move the conditional >> definitions into efi-header.S, taking into account whether CONFIG_EFI is >> enabled or not. > > How many architectures can claim to have both a "magic nop" and a > "mysterious nop", hey? It's fun 'n'all, but putting my serious hat on for a moment, if the name still requires a comment to explain it at point of use, it's not a very good name :( At worst magic_nop is even potentially misleading, since it's not necessarily a nop; there's no mention of the implicit dependency on a context where the side-effect of executing it wouldn't affect anything important. Could we call the macro itself something clear and self-explanatory like efi_signature_insn please? I'm happy for it to be *commented* as "Magic NOP" if you want parity with the VDSO :D Robin. >> Signed-off-by: Ard Biesheuvel >> --- >> arch/arm64/kernel/efi-header.S | 43 +++++++++++++++----- >> arch/arm64/kernel/head.S | 19 +-------- >> 2 files changed, 35 insertions(+), 27 deletions(-) >> >> diff --git a/arch/arm64/kernel/efi-header.S b/arch/arm64/kernel/efi-header.S >> index ddaf57d825b5..7b7ac4316d95 100644 >> --- a/arch/arm64/kernel/efi-header.S >> +++ b/arch/arm64/kernel/efi-header.S >> @@ -7,7 +7,27 @@ >> #include >> #include >> >> + .macro magic_nop >> +#ifdef CONFIG_EFI >> +.L_head: >> + /* >> + * This add instruction has no meaningful effect except that >> + * its opcode forms the magic "MZ" signature required by UEFI. >> + */ >> + add x13, x18, #0x16 > > It's probably faster too ;) > >> +#else >> + /* >> + * Bootloaders may inspect the opcode at the start of the kernel >> + * image to decide if the kernel is capable of booting via UEFI. >> + * So put an ordinary NOP here, not the "MZ.." pseudo-nop above. >> + */ >> + nop > > Let's just hope nobody was decoding the branch instruction... > > Acked-by: Will Deacon >will@kernel.org> > > Will > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel