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 7951CC04FFE for ; Mon, 20 May 2024 13:30:35 +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:Date: Message-ID:From:CC: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=BgOdg1uEgu/TXksGRhx1+8x84UURlgAVQGcvZ6NspvU=; b=on+Kz5PPgxuPQxp+DacAFbyBB7 p7Z1B3t6NMMIzSbVAzf8yNHEq5ZkuAFrNPWDFHWYyPaWEk14T9YPUChzlWaPoe4WqdlBBRzo0VsIn jFqUgnhmQKW/mgZagAFbccXfnquNRyUNkOj5Ny8B+qid6POKTIqaXE8O+1b2UMEWcRNuv6Rhd97ln +ab+mOWvg/73CheQWrprJQ7qbJd2UyiaVLJzuTFSbmD1OpSMr+1GoD70CXTNMTGRZusadN+6oSxfv lvzjnb18az5CiaHQbt5jo2fOgTVE9XcsuYcFp/QtFx1TG1lxIwdXZf+DbCyLIIjHuYVoFhQTQwoW/ LbSDePag==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1s935r-0000000Eau2-305n; Mon, 20 May 2024 13:30:23 +0000 Received: from szxga01-in.huawei.com ([45.249.212.187]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1s935o-0000000EatU-0iby for linux-arm-kernel@lists.infradead.org; Mon, 20 May 2024 13:30:22 +0000 Received: from mail.maildlp.com (unknown [172.19.163.252]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4Vjdd40Q08zvXcX; Mon, 20 May 2024 21:26:32 +0800 (CST) Received: from canpemm500010.china.huawei.com (unknown [7.192.105.118]) by mail.maildlp.com (Postfix) with ESMTPS id C537A180069; Mon, 20 May 2024 21:30:07 +0800 (CST) Received: from [10.67.111.82] (10.67.111.82) by canpemm500010.china.huawei.com (7.192.105.118) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.39; Mon, 20 May 2024 21:30:07 +0800 Subject: Re: [PATCH] arm64: asm-bug: Add .align 2 to the end of __BUG_ENTRY To: Mark Rutland References: <1715955208-17109-1-git-send-email-xiaojiangfeng@huawei.com> CC: , , , , , , , , , , , From: Jiangfeng Xiao Message-ID: <8452c8cb-4822-9110-0a3c-51dd94ee3e8d@huawei.com> Date: Mon, 20 May 2024 21:30:06 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.67.111.82] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To canpemm500010.china.huawei.com (7.192.105.118) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240520_063020_596478_C519FB05 X-CRM114-Status: GOOD ( 31.68 ) 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 2024/5/20 18:33, Mark Rutland wrote: > I reckon we should spell out the reason for this a bit more; would you > be happy with the commit message below? > > | When CONFIG_DEBUG_BUGVERBOSE=n, we fail to add necessary padding bytes > | to bug_table entries, and as a result the last entry in a bug table will > | be ignored, potentially leading to an unexpected panic(). All prior > | entries in the table will be handled correctly. > | > | The arm64 ABI requires that struct fields of up to 8 bytes are > | naturally-aligned, with padding added within a struct such that struct > | are suitably aligned within arrays. > | > | When CONFIG_DEBUG_BUGVERPOSE=y, the layout of a bug_entry is: > | > | struct bug_entry { > | signed int bug_addr_disp; // 4 bytes > | signed int file_disp; // 4 bytes > | unsigned short line; // 2 bytes > | unsigned short flags; // 2 bytes > | } > | > | ... with 12 bytes total, requiring 4-byte alignment. > | > | When CONFIG_DEBUG_BUGVERBOSE=n, the layout of a bug_entry is: > | > | struct bug_entry { > | signed int bug_addr_disp; // 4 bytes > | unsigned short flags; // 2 bytes > | < implicit padding > // 2 bytes > | } > | > | ... with 8 bytes total, with 6 bytes of data and 2 bytes of trailing > | padding, requiring 4-byte alginment. > | > | When we create a bug_entry in assembly, we align the start of the entry > | to 4 bytes, which implicitly handles padding for any prior entries. > | However, we do not align the end of the entry, and so when > | CONFIG_DEBUG_BUGVERBOSE=n, the final entry lacks the trailing padding > | bytes. > | > | For the main kernel image this is not a problem as find_bug() doesn't > | depend on the trailing padding bytes when searching for entries: > | > | for (bug = __start___bug_table; bug < __stop___bug_table; ++bug) > | if (bugaddr == bug_addr(bug)) > | return bug; > | > | However for modules, module_bug_finalize() depends on the trailing > | bytes when calculating the number of entries: > | > | mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry); > | > | ... and as the last bug_entry lacks the necessary padding bytes, this entry > | will not be counted, e.g. in the case of a single entry: > | > | sechdrs[i].sh_size == 6 > | sizeof(struct bug_entry) == 8; > | > | sechdrs[i].sh_size / sizeof(struct bug_entry) == 0; > | > | Consequently module_find_bug() will miss the last bug_entry when it does: > | > | for (i = 0; i < mod->num_bugs; ++i, ++bug) > | if (bugaddr == bug_addr(bug)) > | goto out; > | > | ... which can lead to a kenrel panic due to an unhandled bug. > | > | This can be demonstrated with the following module: > | > | static int __init buginit(void) > | { > | WARN(1, "hello\n"); > | return 0; > | } > | > | static void __exit bugexit(void) > | { > | } > | > | module_init(buginit); > | module_exit(bugexit); > | MODULE_LICENSE("GPL"); > | > | ... which will trigger a kernel panic when loaded: > | > | ------------[ cut here ]------------ > | hello > | Unexpected kernel BRK exception at EL1 > | Internal error: BRK handler: 00000000f2000800 [#1] PREEMPT SMP > | Modules linked in: hello(O+) > | CPU: 0 PID: 50 Comm: insmod Tainted: G O 6.9.1 #8 > | Hardware name: linux,dummy-virt (DT) > | pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > | pc : buginit+0x18/0x1000 [hello] > | lr : buginit+0x18/0x1000 [hello] > | sp : ffff800080533ae0 > | x29: ffff800080533ae0 x28: 0000000000000000 x27: 0000000000000000 > | x26: ffffaba8c4e70510 x25: ffff800080533c30 x24: ffffaba8c4a28a58 > | x23: 0000000000000000 x22: 0000000000000000 x21: ffff3947c0eab3c0 > | x20: ffffaba8c4e3f000 x19: ffffaba846464000 x18: 0000000000000006 > | x17: 0000000000000000 x16: ffffaba8c2492834 x15: 0720072007200720 > | x14: 0720072007200720 x13: ffffaba8c49b27c8 x12: 0000000000000312 > | x11: 0000000000000106 x10: ffffaba8c4a0a7c8 x9 : ffffaba8c49b27c8 > | x8 : 00000000ffffefff x7 : ffffaba8c4a0a7c8 x6 : 80000000fffff000 > | x5 : 0000000000000107 x4 : 0000000000000000 x3 : 0000000000000000 > | x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff3947c0eab3c0 > | Call trace: > | buginit+0x18/0x1000 [hello] > | do_one_initcall+0x80/0x1c8 > | do_init_module+0x60/0x218 > | load_module+0x1ba4/0x1d70 > | __do_sys_init_module+0x198/0x1d0 > | __arm64_sys_init_module+0x1c/0x28 > | invoke_syscall+0x48/0x114 > | el0_svc_common.constprop.0+0x40/0xe0 > | do_el0_svc+0x1c/0x28 > | el0_svc+0x34/0xd8 > | el0t_64_sync_handler+0x120/0x12c > | el0t_64_sync+0x190/0x194 > | Code: d0ffffe0 910003fd 91000000 9400000b (d4210000) > | ---[ end trace 0000000000000000 ]--- > | Kernel panic - not syncing: BRK handler: Fatal exception > | > | Fix this by always aligning the end of a bug_entry to 4 bytes, which is > | correct regardless of CONFIG_DEBUG_BUGVERBOSE. > | > | Fixes: 9fb7410f955f ("arm64/BUG: Use BRK instruction for generic BUG traps") > | Signed-off-by: Yuanbin Xie > | Signed-off-by: Jiangfeng Xiao > > With that: > > Reviewed-by: Mark Rutland > > Mark. > Thank you very much for your patience and professional review. Indeed, we have not clearly expressed the specific layout of `struct bug_entry` under the arm64 ABI and how it causes the problem. We have only briefly described that the assembly code does not consistent with the binary layout of the C struct. Your commit messge is much more accurate in describing the problem, and we couldn't agree more. I will follow your advice to submit our V2 patch. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel