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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7BCFCC636CC for ; Mon, 20 Feb 2023 15:58:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=zjOJbmeX+7/gTGsl7dE0FD8MHt2z8fVF56uPfYpjfiQ=; b=GISGh1WkK7CI16 H7Z9wmObsStZc9OmtSq+Z4/0vmb2cFqy7LYr1aZNgty4858X0sCCqE5ezTTnvuq72zWHA6GXEe/qD lOdMUGsss15qDSfVS3DplWMQv0GcLk7a9WGA59/cV6bHuNrkCGSZTBqK3U7EzOfLd98IEyO4T99sU 0vvt8IDHaKcZUf6bkE+Ccj86zaPsz4PRJcXVa/0e6IEdsdegPHjj8xC6/c4UVC0WxmARVFbgAwJRG UGRih7YLlfw4GowpmtlB3rIrmGO5iknGXYrTccB/rD2F6Wx2GH9gsZTdkVfi6so125NGnGkQyMRg2 F8cPthNReo2Tw9Ysh0pQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pU8XL-004oAs-GH; Mon, 20 Feb 2023 15:57:07 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1pU8XH-004o7P-GL for linux-arm-kernel@lists.infradead.org; Mon, 20 Feb 2023 15:57:05 +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 93C95FEC; Mon, 20 Feb 2023 07:57:37 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.15.112]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7105D3F703; Mon, 20 Feb 2023 07:56:53 -0800 (PST) Date: Mon, 20 Feb 2023 15:56:50 +0000 From: Mark Rutland To: Ard Biesheuvel Cc: syzbot , catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, will@kernel.org Subject: Re: [syzbot] upstream-arm64 build error Message-ID: References: <00000000000028ea4105f4e2ef54@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230220_075703_660034_71E5EF72 X-CRM114-Status: GOOD ( 49.79 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Feb 20, 2023 at 04:38:31PM +0100, Ard Biesheuvel wrote: > On Mon, 20 Feb 2023 at 16:13, Mark Rutland wrote: > > On Mon, Feb 20, 2023 at 02:18:23PM +0100, Ard Biesheuvel wrote: > > > On Mon, 20 Feb 2023 at 14:07, Mark Rutland wrote: > > > > With my config, the Image size is ~242MiB, and I think what's happening is that > > > > some branches from .idmap.text to .text are (possibly) out-of-range, but the > > > > linker doesn't know the final position of the sections yet and hasn't placed > > > > PLTs, and doesn't know the final size of the sections. > > > > > > > > I don't know much about the linker, so that's conjecture, but the below diff > > > > got rid of the build error for me. > > > > > > This issue was reported before here: > > > > > > https://lore.kernel.org/all/CAMj1kXGAf7ikEU5jLoik0xrOde0xBg0yJkOo5=PtEtNXoUxMXA@mail.gmail.com/ > > > > > > and the bisect ended up somewhere else. > > > > Ah, sorry; I hadn't spotted that. > > > > > The issue seems to be where exactly the veneers for the entire image > > > are dumped, and when this is right after .idmap.text (being the last > > > input section with the EXEC ELF attribute), it pushes the > > > __idmap_text_end symbol over the next 4k boundary. > > > > I'm a bit confused as to why veneers for other sections would be dropped in > > here. Note that these branches (for-next/core and for-kernelci) have your patch > > moving IDMAP_TEXT into .rodata, so that's no longer the last input section with > > the EXEC attribute, unless I've misunderstood? > > > > Perhaps that's meant to be read as the last input section *within a given > > output section* ? > > The issue seems subtly different in this case: > > .idmap.text 0xffffffc01e48e5c0 0x32c arch/arm64/mm/proc.o > 0xffffffc01e48e5c0 idmap_cpu_replace_ttbr1 > 0xffffffc01e48e600 idmap_kpti_install_ng_mappings > 0xffffffc01e48e800 __cpu_setup > *fill* 0xffffffc01e48e8ec 0x4 > .idmap.text.stub > 0xffffffc01e48e8f0 0x18 linker stubs > 0xffffffc01e48f8f0 __idmap_text_end = . > 0xffffffc01e48f000 . = ALIGN (0x1000) > *fill* 0xffffffc01e48f8f0 0x710 > 0xffffffc01e490000 idmap_pg_dir = . > > So here, there is 0x18 bytes of stubs, but for some reason, it ends up > bumping the output pointer by an additional 4k. Yeah, the 4K bump is bizarre, especially since it's literally +4K and not an align upwards to the next 4K boundary. > > If marking the .idmap.text section as non-executable prevents other veneers > > from being collected there, then I reckon that doing that along with the > > indirect branches using adr_l + blr should be sufficient? That way there should > > be no veneers dropped into .idmap.text, and the cost of ADRP+ADD+BLR in a > > one-time boot path isn't going to be noticeable. > > > > I guess but I hate making that kind of changes just to make a > theoretical boot target that nobody uses build. I appreciate it's niche, but this is a configuration I've been using for testing for several years (see my fuzzing/* and testing/* branches on kernel.org), so it's not quite "nobody" unless that was an a judgement on my popularity. ;) I'm going to assume that means if I clean this up and post as a proper patch you're not going to NAK it. :) > > FWIW, If I modify head.S to replace: > > > > .section ".idmap.text","a" > > > > With: > > > > .section ".idmap.text","a" > > > > You mean ax -> a right? That seems like a reasonable change as long as > we apply it everywhere, but it would be nice if we wouldn't need it. Yes, sorry, It's currently "awx", and AFAICT we need neither the "w" nor the "x". > > Then the only branches which don't get PLTs are the ones I mentioned earlier, > > and the linker complains about those becoming truncated: > > > > | [mark@lakrids:~/src/linux]% usekorg 12.1.0 make ARCH=arm64 CROSS_COMPILE=aarch64-linux- -j50 Image > > | CALL scripts/checksyscalls.sh > > | LDS arch/arm64/kernel/vmlinux.lds > > | AS arch/arm64/kernel/head.o > > | AR arch/arm64/kernel/built-in.a > > | AR arch/arm64/built-in.a > > | AR built-in.a > > | AR vmlinux.a > > | LD vmlinux.o > > | OBJCOPY modules.builtin.modinfo > > | GEN modules.builtin > > | MODPOST vmlinux.symvers > > | UPD include/generated/utsversion.h > > | CC init/version-timestamp.o > > | LD .tmp_vmlinux.kallsyms1 > > | arch/arm64/kernel/head.o: in function `primary_entry': > > | (.idmap.text+0x1c): relocation truncated to fit: R_AARCH64_CALL26 against symbol `dcache_clean_poc' defined in .text section in arch/arm64/mm/cache.o > > | arch/arm64/kernel/head.o: in function `init_el2': > > | (.idmap.text+0x88): relocation truncated to fit: R_AARCH64_CALL26 against symbol `dcache_clean_poc' defined in .text section in arch/arm64/mm/cache.o > > | make[1]: *** [scripts/Makefile.vmlinux:34: vmlinux] Error 1 > > | make: *** [Makefile:1252: vmlinux] Error 2 > > > > Is there any reason we need the "wx" attributs for .idmap.text? > > It doesn't really matter - we place these input sections explicitly anyway. That was my assumption; just checking I haven't missed a subtlety where this would affect assembler or linker behaviour undesireably. Thanks, Mark. > > With that in mind, does the below look ok? It builds cleanly and boots fine for > > me with GCC 12.1.0 atop for-next/core. > > > > We could wrap the adr_l + blr into a blr_l macro for legibility. > > > > Thanks, > > Mark. > > > > ---->8---- > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > > index 212d93aca5e61..b98970907226b 100644 > > --- a/arch/arm64/kernel/head.S > > +++ b/arch/arm64/kernel/head.S > > @@ -70,7 +70,7 @@ > > > > __EFI_PE_HEADER > > > > - .section ".idmap.text","awx" > > + .section ".idmap.text","a" > > > > /* > > * The following callee saved general purpose registers are used on the > > @@ -99,7 +99,8 @@ SYM_CODE_START(primary_entry) > > cbz x19, 0f > > adrp x0, __idmap_text_start > > adr_l x1, __idmap_text_end > > - bl dcache_clean_poc > > + adr_l x2, dcache_clean_poc > > + blr x2 > > 0: mov x0, x19 > > bl init_kernel_el // w0=cpu_boot_mode > > mov x20, x0 > > @@ -527,7 +528,7 @@ SYM_FUNC_END(__primary_switched) > > * end early head section, begin head code that is also used for > > * hotplug and needs to have the same protections as the text region > > */ > > - .section ".idmap.text","awx" > > + .section ".idmap.text","a" > > > > /* > > * Starting from EL2 or EL1, configure the CPU to execute at the highest > > @@ -566,7 +567,8 @@ SYM_INNER_LABEL(init_el2, SYM_L_LOCAL) > > cbz x0, 0f > > adrp x0, __hyp_idmap_text_start > > adr_l x1, __hyp_text_end > > - bl dcache_clean_poc > > + adr_l x2, dcache_clean_poc > > + blr x2 > > 0: > > mov_q x0, HCR_HOST_NVHE_FLAGS > > msr hcr_el2, x0 > > @@ -728,7 +730,7 @@ SYM_FUNC_END(set_cpu_boot_mode_flag) > > * Checks if the selected granule size is supported by the CPU. > > * If it isn't, park the CPU > > */ > > - .section ".idmap.text","awx" > > + .section ".idmap.text","a" > > SYM_FUNC_START(__enable_mmu) > > mrs x3, ID_AA64MMFR0_EL1 > > ubfx x3, x3, #ID_AA64MMFR0_EL1_TGRAN_SHIFT, 4 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel