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 685A9C433EF for ; Mon, 21 Feb 2022 17:33:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229706AbiBURdu (ORCPT ); Mon, 21 Feb 2022 12:33:50 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:41926 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236892AbiBURdr (ORCPT ); Mon, 21 Feb 2022 12:33:47 -0500 Received: from mx1.molgen.mpg.de (mx3.molgen.mpg.de [141.14.17.11]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A263F1B7BE; Mon, 21 Feb 2022 09:33:08 -0800 (PST) Received: from [192.168.0.2] (ip5f5aee3b.dynamic.kabel-deutschland.de [95.90.238.59]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: pmenzel) by mx.molgen.mpg.de (Postfix) with ESMTPSA id DEA1761E64846; Mon, 21 Feb 2022 18:33:05 +0100 (CET) Message-ID: <5fa42fd8-8a9b-b37c-5310-c3005f0f4b69@molgen.mpg.de> Date: Mon, 21 Feb 2022 18:33:05 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: BUG: Kernel NULL pointer dereference on write at 0x00000000 (rtmsg_ifinfo_build_skb) Content-Language: en-US To: Nathan Chancellor Cc: Zhouyi Zhou , "Paul E. McKenney" , Josh Triplett , rcu@vger.kernel.org, LKML , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org, Nick Desaulniers , llvm@lists.linux.dev, Fangrui Song 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> <265b1953-36b4-6a65-1a36-67a61248f27f@molgen.mpg.de> From: Paul Menzel In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Dear Nathan, Am 21.02.22 um 16:29 schrieb Nathan Chancellor: > On Mon, Feb 21, 2022 at 12:17:40PM +0100, Paul Menzel wrote: >> Am 17.02.22 um 02:16 schrieb Nathan Chancellor: >> >>> On Wed, Feb 16, 2022 at 02:19:51PM +0100, Paul Menzel wrote: >>>> [Cc: +LLVM/clang build support folks] >> >> […] >> >>>> 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 ;) >> >> Thank you for looking into this, and sharing your analysis. >> >> I built LLVM/clang from the master branch, rebuilt, but can still reproduce >> this. >> >> $ git clone --depth=1 https://github.com/llvm/llvm-project.git >> $ cd llvm-project/ >> $ git log --oneline >> 41cb504b7 [mlir][linalg][bufferize][NFC] Move interface impl to Linalg Transforms >> $ mkdir build >> $ cd build >> $ cmake -DLLVM_ENABLE_PROJECTS=clang -G "Unix Makefiles" > > Since this is something related to ld.lld, not clang, this should be: > > ... -DLLVM_ENABLE_PROJECTS="clang;lld" ... > >> -DCMAKE_BUILD_TYPE=Release -DLLVM_INSTALL_UTILS=ON >> -DCMAKE_INSTALL_PREFIX=/scratch/local2/llvm ../llvm >> $ make -j20 >> $ make -j20 clang-check > > You can also do 'check-lld' if you want. > >> $ make install >> $ /scratch/local2/llvm/bin/clang --version >> clang version 15.0.0 (https://github.com/llvm/llvm-project.git 41cb504b7c4b18ac15830107431a0c1eec73a6b2) >> Target: powerpc64le-unknown-linux-gnu >> Thread model: posix >> InstalledDir: /scratch/local2/llvm/bin >> >> Then build Linux after `make clean` with `/scratch/local2/llvm/bin` in the >> path. >> >> $ LLVM=1 LLVM_IAS=0 eatmydata make -j20 >> >> $ qemu-system-ppc64 -enable-kvm -nographic -smp cores=1,threads=1 -net none -enable-kvm -M pseries -nodefaults -device spapr-vscsi -serial stdio -m 512 -kernel /dev/shm/linux/vmlinux -append "debug_boot_weak_hash panic=-1 console=ttyS0 rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 rcupdate.rcu_self_test=1 rcutorture.onoff_interval=1000 rcutorture.onoff_holdoff=30 rcutorture.n_barrier_cbs=4 rcutorture.stat_interval=15 rcutorture.shutdown_secs=420 rcutorture.test_no_idle_hz=1 rcutorture.verbose=1" >> […] >> Preparing to boot Linux version 5.17.0-rc5-00178-ga4b9a8fb20e7 (pmenzel@flughafenberlinbrandenburgwillybrandt.molgen.mpg.de) (clang version 15.0.0 (https://github.com/llvm/llvm-project.git 41cb504b7c4b18ac15830107431a0c1eec73a6b2), LLD 13.0.0) #29 SMP PREEMPT Mon > > ^ still using ld.lld 13.0.0. > > If you want to test the master branch, I would checkout LLVM at > 460830a9c664e8cce959c660648faa7747ad8bdc, as the next commit introduces > a boot regression unrelated to this issue: > > https://github.com/ClangBuiltLinux/linux/issues/1581 > > That should at least confirm this is resolved in a newer release. Sorry for missing to update ld.lld. Indeed with the commit you mentioned, the segmentation fault is gone. $ /scratch/local2/llvm/bin/ld.lld --version LLD 14.0.0 (compatible with GNU linkers) >> Feb 21 10:58:54 CET 2022 >> […] >> [ 0.465889][ T1] BUG: Kernel NULL pointer dereference on read at 0x00000000 >> [ 0.466749][ T1] Faulting instruction address: 0xc0000000008fc300 >> [ 0.467507][ T1] Oops: Kernel access of bad area, sig: 11 [#1] >> […] > > I do intend to do further analysis at some point over the next few days > to see if I can figure out exactly why that commit that I mentioned > above fixes the issue then we can look into what we should do about it > in the kernel sources. Awesome. Thank you for working on that. Kind regards, Paul