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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72D93C433EF for ; Thu, 17 Feb 2022 01:16:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230106AbiBQBQb (ORCPT ); Wed, 16 Feb 2022 20:16:31 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:54096 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229854AbiBQBQb (ORCPT ); Wed, 16 Feb 2022 20:16:31 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B3A429B9E7; Wed, 16 Feb 2022 17:16:17 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 000A2B820B0; Thu, 17 Feb 2022 01:16:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 75EBFC340EC; Thu, 17 Feb 2022 01:16:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1645060574; bh=xYn+gAhFNelcYMGtcx1zuj5mBydfNAevycx/MBcfC68=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uKAQUccZRq0RXPgD7LNGAfplDAh1BRFoVsNIm/4QV8+3/RLPTrgV8xtMHtdxiW7F6 f8CJrfoXWiNrjQ3RZlvKNZnJlQlZQOew3j/z/AK/y68iIMuf5i0H7nBe36QXbBLH6R tHBLLg0QdJXxhuLx6oywctq17nLqN00kXUw3Bw0bIgkJ6v4/EUTE3Ya9XXlJjPcQ+4 rNAeqsjfQ6J2FFR4wTdhqt2wG3fSwQr91iQsWxg4FmtTc2kAi+tUuoLIf+nVWR+xKB m7lDT+6n5NY9Ejk8zePiCP7Piwt6+NjgkncRfvM3nRXdVNEBPbhIM/Hitu6RkJu6bo +i9AkVF0qKk7w== Date: Wed, 16 Feb 2022 18:16:09 -0700 From: Nathan Chancellor To: Paul Menzel Cc: Zhouyi Zhou , "Paul E. McKenney" , Josh Triplett , rcu , LKML , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org, Nick Desaulniers , llvm@lists.linux.dev Subject: Re: BUG: Kernel NULL pointer dereference on write at 0x00000000 (rtmsg_ifinfo_build_skb) Message-ID: References: <159db05f-539c-fe29-608b-91b036588033@molgen.mpg.de> <3534d781-7d01-b42a-8974-0b1c367946f0@molgen.mpg.de> <04a597dc-64aa-57e6-f7fb-17bd2ec58159@molgen.mpg.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Hi Paul, On Wed, Feb 16, 2022 at 02:19:51PM +0100, Paul Menzel wrote: > [Cc: +LLVM/clang build support folks] > > > Dear Zhouyi, dear Nathan, dear Nick, > > > To recap: On a ppc64le machine, building Linux in Ubuntu 21.10 with *llvm* > and *clang* 1:13.0-53~exp1 > > $ clang --version > Ubuntu clang version 13.0.0-2 > Target: powerpc64le-unknown-linux-gnu > Thread model: posix > InstalledDir: /usr/bin > > results in a segmentation fault, while it works when building with GCC. > > $ gcc --version > gcc (Ubuntu 11.2.0-7ubuntu2) 11.2.0 Thank you for keying us in. I am going to have a bit of a brain dump here based on the information I have uncovered after a couple of hours of debugging. TL;DR: It seems like something is broken with __read_mostly + ld.lld before 14.0.0. My initial reproduction steps (boot-qemu.sh comes from https://github.com/ClangBuiltLinux/boot-utils): $ clang --version clang version 13.0.1 (Fedora 13.0.1-1.fc37) Target: x86_64-redhat-linux-gnu Thread model: posix InstalledDir: /usr/bin $ powerpc64le-linux-gnu-as --version GNU assembler version 2.37-2.fc36 Copyright (C) 2021 Free Software Foundation, Inc. This program is free software; you may redistribute it under the terms of the GNU General Public License version 3 or later. This program has absolutely no warranty. This assembler was configured for a target of `powerpc64le-linux-gnu'. $ curl -LSso .config https://lore.kernel.org/all/f41550c7-26c0-cf81-7de9-aa924434a565@molgen.mpg.de/3-linux-5.17-rc4-rcu-dev-config.txt $ scripts/config --set-val INITRAMFS_SOURCE '""' $ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 LLVM_IAS=0 all $ boot-qemu.sh -a ppc64le -k . -t 45s QEMU location: /usr/bin QEMU version: QEMU emulator version 6.2.0 (qemu-6.2.0-5.fc37) + timeout --foreground 45s stdbuf -oL -eL qemu-system-ppc64 -initrd \ /home/nathan/cbl/github/boot-utils-ro/images/ppc64le/rootfs.cpio -device \ ipmi-bmc-sim,id=bmc0 -device isa-ipmi-bt,bmc=bmc0,irq=10 -L \ /home/nathan/cbl/github/boot-utils-ro/images/ppc64le/ -bios skiboot.lid \ -machine powernv8 -display none -kernel \ /home/nathan/cbl/src/linux/arch/powerpc/boot/zImage.epapr -m 2G \ -nodefaults -serial mon:stdio ... [ 1.478028][ T1] BUG: Kernel NULL pointer dereference on read at 0x00000000 [ 1.478630][ T1] Faulting instruction address: 0xc00000000090bee0 [ 1.479521][ T1] Oops: Kernel access of bad area, sig: 11 [#1] [ 1.480036][ T1] LE PAGE_SIZE=64K MMU=Hash PREEMPT SMP NR_CPUS=16 NUMA PowerNV [ 1.480853][ T1] Modules linked in: [ 1.481265][ T1] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.17.0-rc4-00001-gfa15c7cb550f #1 [ 1.481967][ T1] NIP: c00000000090bee0 LR: c000000000d96b60 CTR: c0000000000d5b4c [ 1.482596][ T1] REGS: c000000007443330 TRAP: 0380 Not tainted (5.17.0-rc4-00001-gfa15c7cb550f) [ 1.483305][ T1] MSR: 9000000002009033 CR: 22800a87 XER: 00000000 [ 1.484277][ T1] CFAR: c000000000d96b5c IRQMASK: 0 [ 1.484277][ T1] GPR00: c000000000d96b54 c0000000074435d0 c0000000028bc600 0000000000000000 [ 1.484277][ T1] GPR04: ffffffffffffffff ffffffffff1ea558 ffffffffff1ebfe4 c00000000261ae88 [ 1.484277][ T1] GPR08: 0000000000000003 0000000000000004 c00000000261ae88 0000000000000000 [ 1.484277][ T1] GPR12: 0000000000800000 c000000002a60000 c000000000012518 0000000000000000 [ 1.484277][ T1] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 1.484277][ T1] GPR20: 0000000000000000 c0000000027bff80 0000000000000cc0 0000000000000000 [ 1.484277][ T1] GPR24: 0000000000000010 0000000000000000 0000000000000000 0000000000000000 [ 1.484277][ T1] GPR28: c0000000028fcfd8 c000000007b83000 0000000000000000 c0000000074435d0 [ 1.490325][ T1] NIP [c00000000090bee0] strlen+0x10/0x30 [ 1.490788][ T1] LR [c000000000d96b60] if_nlmsg_size+0x2b0/0x390 [ 1.491319][ T1] Call Trace: [ 1.491573][ T1] [c0000000074435d0] [c000000000d96b54] if_nlmsg_size+0x2a4/0x390 (unreliable) [ 1.492291][ T1] [c000000007443680] [c000000000d96790] rtmsg_ifinfo_build_skb+0x80/0x1a0 [ 1.492958][ T1] [c000000007443740] [c000000000d97590] rtmsg_ifinfo+0x70/0xd0 [ 1.493559][ T1] [c000000007443790] [c000000000d7d528] register_netdevice+0x5d8/0x670 [ 1.494205][ T1] [c000000007443820] [c000000000d7d94c] register_netdev+0x4c/0x80 [ 1.494823][ T1] [c000000007443850] [c000000000f826d8] sit_init_net+0x1b8/0x200 [ 1.495426][ T1] [c0000000074438d0] [c000000000d63b5c] ops_init+0x14c/0x1c0 [ 1.496014][ T1] [c000000007443930] [c000000000d6314c] register_pernet_operations+0xec/0x1e0 [ 1.496716][ T1] [c000000007443990] [c000000000d633d0] register_pernet_device+0x60/0xd0 [ 1.497372][ T1] [c0000000074439e0] [c000000002085194] sit_init+0x54/0x160 [ 1.497950][ T1] [c000000007443a70] [c000000000011c58] do_one_initcall+0x108/0x3e0 [ 1.498573][ T1] [c000000007443c70] [c000000002006190] do_initcall_level+0xe4/0x1c4 [ 1.499219][ T1] [c000000007443cc0] [c00000000200604c] do_initcalls+0x84/0xe4 [ 1.499799][ T1] [c000000007443d40] [c000000002005da8] kernel_init_freeable+0x160/0x1ec [ 1.500444][ T1] [c000000007443da0] [c00000000001254c] kernel_init+0x3c/0x270 [ 1.501042][ T1] [c000000007443e10] [c00000000000cd64] ret_from_kernel_thread+0x5c/0x64 [ 1.501721][ T1] Instruction dump: [ 1.502202][ T1] eb81ffe0 7c0803a6 4e800020 00000000 00000000 00000000 60000000 60000000 [ 1.502934][ T1] 3883ffff 60000000 60000000 60000000 <8ca40001> 28050000 4082fff8 7c632050 [ 1.504028][ T1] ---[ end trace 0000000000000000 ]--- ... First thing was figuring out where the NULL pointer dereference happens, which appears to the "strlen(ops->kind)" in rtnl_link_get_size(): 515 static size_t rtnl_link_get_size(const struct net_device *dev) 516 { 517 const struct rtnl_link_ops *ops = dev->rtnl_link_ops; 518 size_t size; 519 520 if (!ops) 521 return 0; 522 523 size = nla_total_size(sizeof(struct nlattr)) + /* IFLA_LINKINFO */ 524 nla_total_size(strlen(ops->kind) + 1); /* IFLA_INFO_KIND */ which I confirmed some really rudimentary printk debugging: [ 1.476862][ T1] nathan: rtnl_link_get_size(): name: sit0, ops: c0000000028fcfd8, ops->kind: (null) diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c index 710da8a36729..c8d928e83aec 100644 --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -520,6 +520,9 @@ static size_t rtnl_link_get_size(const struct net_device *dev) if (!ops) return 0; + pr_err("nathan: %s(): name: %s, ops: %px, ops->kind: %s\n", __func__, + dev->name, ops, ops->kind); + size = nla_total_size(sizeof(struct nlattr)) + /* IFLA_LINKINFO */ nla_total_size(strlen(ops->kind) + 1); /* IFLA_INFO_KIND */ Okay... how did sit0 end up with a NULL kind...? It is very clearly defined as "sit": 1830 static struct rtnl_link_ops sit_link_ops __read_mostly = { 1831 .kind = "sit", Adding some more debug prints to net/ipv6/sit.c: diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c index c0b138c20992..7b9edbed2fcd 100644 --- a/net/ipv6/sit.c +++ b/net/ipv6/sit.c @@ -1920,6 +1920,12 @@ static int __net_init sit_init_net(struct net *net) */ sitn->fb_tunnel_dev->features |= NETIF_F_NETNS_LOCAL; + pr_err("nathan: %s(): &sit_link_ops: %px\n", __func__, &sit_link_ops); + pr_err("nathan: %s(): sit_link_ops.kind: %s\n", __func__, sit_link_ops.kind); + pr_err("nathan: %s(): sit_link_ops.maxtype: %u\n", __func__, sit_link_ops.maxtype); + pr_err("nathan: %s(): sitn->fb_tunnel_dev->rtnl_link_ops: %px\n", __func__, sitn->fb_tunnel_dev->rtnl_link_ops); + pr_err("nathan: %s(): sitn->fb_tunnel_dev->rtnl_link_ops->kind: %s\n", __func__, sitn->fb_tunnel_dev->rtnl_link_ops->kind); + err = register_netdev(sitn->fb_tunnel_dev); if (err) goto err_reg_dev; reveals: [ 1.471920][ T1] sit: nathan: sit_init_net(): &sit_link_ops: c0000000028fcfd8 [ 1.472534][ T1] sit: nathan: sit_init_net(): sit_link_ops.kind: (null) [ 1.473088][ T1] sit: nathan: sit_init_net(): sit_link_ops.maxtype: 20 [ 1.473639][ T1] sit: nathan: sit_init_net(): sitn->fb_tunnel_dev->rtnl_link_ops: c0000000028fcfd8 [ 1.474370][ T1] sit: nathan: sit_init_net(): sitn->fb_tunnel_dev->rtnl_link_ops->kind: (null) This is super bizarre, as the maxtype member appears to have the correct value, but how is kind's initial getting dropped on the floor? Removing the __read_mostly annotation "fixes" it: [ 1.481708][ T1] sit: nathan: sit_init_net(): &sit_link_ops: c0000000027d3f60 [ 1.482319][ T1] sit: nathan: sit_init_net(): sit_link_ops.kind: sit [ 1.482878][ T1] sit: nathan: sit_init_net(): sit_link_ops.maxtype: 20 [ 1.483429][ T1] sit: nathan: sit_init_net(): sitn->fb_tunnel_dev->rtnl_link_ops: c0000000027d3f60 [ 1.484174][ T1] sit: nathan: sit_init_net(): sitn->fb_tunnel_dev->rtnl_link_ops->kind: sit ... Linux version 5.17.0-rc4-00001-g956f02ad5c31-dirty (nathan@dev-fedora.archlinux-ax161) (clang version 13.0.1 (Fedora 13.0.1-1.fc37), LLD 13.0.1) #2 SMP PREEMPT Wed Feb 16 13:29:49 MST 2022 ... diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c index 7b9edbed2fcd..f109c7a0233b 100644 --- a/net/ipv6/sit.c +++ b/net/ipv6/sit.c @@ -70,7 +70,7 @@ static void ipip6_tunnel_setup(struct net_device *dev); static void ipip6_dev_free(struct net_device *dev); static bool check_6rd(struct ip_tunnel *tunnel, const struct in6_addr *v6dst, __be32 *v4dst); -static struct rtnl_link_ops sit_link_ops __read_mostly; +static struct rtnl_link_ops sit_link_ops; static unsigned int sit_net_id __read_mostly; struct sit_net { @@ -1827,7 +1827,7 @@ static void ipip6_dellink(struct net_device *dev, struct list_head *head) unregister_netdevice_queue(dev, head); } -static struct rtnl_link_ops sit_link_ops __read_mostly = { +static struct rtnl_link_ops sit_link_ops = { .kind = "sit", .maxtype = IFLA_IPTUN_MAX, .policy = ipip6_policy, Switching to ld.bfd also resolves it: [ 1.470405][ T1] sit: nathan: sit_init_net(): &sit_link_ops: c0000000028acfd8 [ 1.471016][ T1] sit: nathan: sit_init_net(): sit_link_ops.kind: sit [ 1.471534][ T1] sit: nathan: sit_init_net(): sit_link_ops.maxtype: 20 [ 1.472062][ T1] sit: nathan: sit_init_net(): sitn->fb_tunnel_dev->rtnl_link_ops: c0000000028acfd8 [ 1.472790][ T1] sit: nathan: sit_init_net(): sitn->fb_tunnel_dev->rtnl_link_ops->kind: sit ... Linux version 5.17.0-rc4-00001-g956f02ad5c31 (nathan@dev-fedora.archlinux-ax161) (clang version 13.0.1 (Fedora 13.0.1-1.fc37), GNU ld version 2.37-2.fc36) #3 SMP PREEMPT Wed Feb 16 13:33:42 MST 2022 ... I tested with ToT LLVM (or at least, close to it, since there is an unrelated ld.lld regression there) and I could not reproduce it there, so I did a reverse bisect to see what commit fixes this issue in LLVM 14 and I landed on: commit 55c14d6dbfd8e7b86c15d2613fea3490078e2ae4 Author: Fangrui Song Date: Thu Nov 25 14:12:34 2021 -0800 [ELF] Simplify DynamicSection content computation. NFC The new code computes the content twice, but avoides the tricky std::function. Removed 13KiB code in a Release build. lld/ELF/SyntheticSections.cpp | 117 ++++++++++++++++-------------------------- lld/ELF/SyntheticSections.h | 12 +---- 2 files changed, 44 insertions(+), 85 deletions(-) That's... interesting, given that commit title says No Functional Change, even though there clearly is one. That commit has a couple mentions of PowerPC synthetic sections, so it is possible that the new content calculation lines up with ld.bfd? I am not really sure where to go from here, as I don't fully understand what the problem was before that LLD change. I'll see if I can do some more investigation tomorrow (unless someone wants to beat me to it ;) Cheers, Nathan