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 7EDBFC04FFE for ; Mon, 20 May 2024 12:06:09 +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-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:From:References:CC:To:Subject: MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=OhuEe2c9854nVtZSIMz/bvvDHjas7G4Ttc8/JnuSj/4=; b=sP4bGFX/7X3Ktl NOtlO0RHe2NclLIQNGJlbqvX8nxcr3WvyShtbDpTa5nMQh4MFq0lCydzwiiPgsGIA31TkDMO5Vlkm OcqntI48dlzoRicFni+ukLp7pXDRWsqKKCaAGrSPmR0Agn0S8goQh5s+XVM79InJhvRzYHXH5dYut jkHGQdhFQLxBUze7ztr4LcuXtgPY2V2z9x2lpylFXl7KTlH7vkyLCAbayiE5oiAwhnK9TuLKxL0Oj QEg4IZKalkflryt7CaHDpU/WTGwwyzJ4wha6RwcK46ojAXft1+d3HnpuL/gMfet064d/+VbGy4eEy 9vkdBcTbLyA9N50mKsWQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1s91m9-0000000EP8M-1W3W; Mon, 20 May 2024 12:05:57 +0000 Received: from szxga02-in.huawei.com ([45.249.212.188]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1s91m5-0000000EP73-3oWR for linux-arm-kernel@lists.infradead.org; Mon, 20 May 2024 12:05:56 +0000 Received: from mail.maildlp.com (unknown [172.19.88.105]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4VjbpK2hp0zcj3D; Mon, 20 May 2024 20:04:25 +0800 (CST) Received: from kwepemd500012.china.huawei.com (unknown [7.221.188.25]) by mail.maildlp.com (Postfix) with ESMTPS id 0E3681402C8; Mon, 20 May 2024 20:05:27 +0800 (CST) Received: from [10.67.111.176] (10.67.111.176) by kwepemd500012.china.huawei.com (7.221.188.25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.34; Mon, 20 May 2024 20:05:26 +0800 Message-ID: <20d70835-9411-9a08-c567-56d7040e01dd@huawei.com> Date: Mon, 20 May 2024 20:05:25 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.3.0 Subject: Re: [PATCH] arm64: asm-bug: Add .align 2 to the end of __BUG_ENTRY To: Mark Rutland , Jiangfeng Xiao CC: , , , , , , , , , , , , "zhangjianhua (E)" References: <1715955208-17109-1-git-send-email-xiaojiangfeng@huawei.com> Content-Language: en-US From: Li Zetao In-Reply-To: X-Originating-IP: [10.67.111.176] X-ClientProxiedBy: dggpeml500015.china.huawei.com (7.185.36.226) To kwepemd500012.china.huawei.com (7.221.188.25) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240520_050554_349122_73137DCB X-CRM114-Status: GOOD ( 39.74 ) 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-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 Hi, On 2024/5/20 18:33, Mark Rutland wrote: > On Fri, May 17, 2024 at 10:13:28PM +0800, Jiangfeng Xiao wrote: >> I'm using the latest linux kernel mainline code, >> with the default arm64 configuration: >> make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfig, >> and set CONFIG_EXPERT=y, CONFIG_DEBUG_BUGVERBOSE=n, >> CONFIG_PANIC_ON_OOPS=y. >> >> Loading the following kernel module will cause kernel panic. >> >> The call stack is as follows: >> >> root@(none):/# /root/insmod hello.ko >> [ 6.035003] hello: loading out-of-tree module taints kernel. >> [ 6.039129] ------------[ cut here ]------------ >> [ 6.039287] hello >> [ 6.039704] Unexpected kernel BRK exception at EL1 >> [ 6.040059] Internal error: BRK handler: 00000000f2000800 [#1] PREEMPT SMP >> [ 6.040457] Modules linked in: hello(O+) >> [ 6.041311] CPU: 0 PID: 50 Comm: insmod Tainted: G O 6.9.1 #8 >> [ 6.041755] Hardware name: linux,dummy-virt (DT) >> [ 6.042238] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) >> [ 6.042594] pc : buginit+0x18/0x1000 [hello] >> [ 6.043601] lr : buginit+0x18/0x1000 [hello] >> [ 6.043852] sp : ffff800080533ae0 >> [ 6.044121] x29: ffff800080533ae0 x28: 0000000000000000 x27: 0000000000000000 >> [ 6.044523] x26: ffffaba8c4e70510 x25: ffff800080533c30 x24: ffffaba8c4a28a58 >> [ 6.044961] x23: 0000000000000000 x22: 0000000000000000 x21: ffff3947c0eab3c0 >> [ 6.045503] x20: ffffaba8c4e3f000 x19: ffffaba846464000 x18: 0000000000000006 >> [ 6.046124] x17: 0000000000000000 x16: ffffaba8c2492834 x15: 0720072007200720 >> [ 6.046387] x14: 0720072007200720 x13: ffffaba8c49b27c8 x12: 0000000000000312 >> [ 6.046829] x11: 0000000000000106 x10: ffffaba8c4a0a7c8 x9 : ffffaba8c49b27c8 >> [ 6.047293] x8 : 00000000ffffefff x7 : ffffaba8c4a0a7c8 x6 : 80000000fffff000 >> [ 6.047739] x5 : 0000000000000107 x4 : 0000000000000000 x3 : 0000000000000000 >> [ 6.047955] x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff3947c0eab3c0 >> [ 6.048366] Call trace: >> [ 6.048653] buginit+0x18/0x1000 [hello] >> [ 6.048922] do_one_initcall+0x80/0x1c8 >> [ 6.049333] do_init_module+0x60/0x218 >> [ 6.049475] load_module+0x1ba4/0x1d70 >> [ 6.049755] __do_sys_init_module+0x198/0x1d0 >> [ 6.049959] __arm64_sys_init_module+0x1c/0x28 >> [ 6.050160] invoke_syscall+0x48/0x114 >> [ 6.050334] el0_svc_common.constprop.0+0x40/0xe0 >> [ 6.050468] do_el0_svc+0x1c/0x28 >> [ 6.050635] el0_svc+0x34/0xd8 >> [ 6.050852] el0t_64_sync_handler+0x120/0x12c >> [ 6.051088] el0t_64_sync+0x190/0x194 >> [ 6.051433] Code: d0ffffe0 910003fd 91000000 9400000b (d4210000) >> [ 6.052212] ---[ end trace 0000000000000000 ]--- >> [ 6.052473] Kernel panic - not syncing: BRK handler: Fatal exception >> >> The kernel module source code is as follows: >> ``` >> >> 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"); >> ``` >> >> When CONFIG_DEBUG_BUGVERBOSE macro is disabled, >> the size of "__bug_table" section in hello.ko >> is only 6 bytes instead of the expected 8 bytes. >> As a result, >> mod->num_bugs = sechdrs[i].sh_size / sizeof(struct bug_entry) = 6 / 8 = 0 >> calculated in module_bug_finalize when the kernel loads ko is incorrect. >> >> When running `WARN()`, the following backtrace is triggered: >> >> module_find_bug() at lib/bug.c >> find_bug() at lib/bug.c >> __report_bug() at lib/bug.c >> report_bug() at lib/bug.c >> call_break_hook() at arch/arm64/kernel/debug-monitors.c >> brk_handler() at arch/arm64/kernel/debug-monitors.c >> >> It will return -EFAULT because hello.ko's mod->num_bugs is 0. >> Finally, the kernel OOPS is triggered. >> >> Add .align 2 to the end of __BUG_ENTRY >> to make the object layout generated by the assembly code >> consistent with that of the C struct bug_entry. >> >> Fixes: 9fb7410f955f ("arm64/BUG: Use BRK instruction for generic BUG traps") >> >> Signed-off-by: Yuanbin Xie >> Signed-off-by: Jiangfeng Xiao >> --- >> arch/arm64/include/asm/asm-bug.h | 1 + >> 1 file changed, 1 insertion(+) > > Ouch; sorry about this. > > 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. > >> >> >> >> diff --git a/arch/arm64/include/asm/asm-bug.h b/arch/arm64/include/asm/asm-bug.h >> index c762038..6e73809 100644 >> --- a/arch/arm64/include/asm/asm-bug.h >> +++ b/arch/arm64/include/asm/asm-bug.h >> @@ -28,6 +28,7 @@ >> 14470: .long 14471f - .; \ >> _BUGVERBOSE_LOCATION(__FILE__, __LINE__) \ >> .short flags; \ >> + .align 2; \ The use of .align 2 here is based on the assumption that struct bug_entry is 4-byte aligned. Currently, there is no problem with this assumption, but for compatibility reasons, refer to the riscv architecture and refactor the implementation of __BUG_FLAGS: #define __BUG_FLAGS(flags) \ do { \ __asm__ __volatile__ ( \ "1:\n\t" \ "ebreak\n" \ ".pushsection __bug_table,\"aw\"\n\t" \ "2:\n\t" \ __BUG_ENTRY "\n\t" \ ".org 2b + %3\n\t" \ ".popsection" \ : \ : "i" (__FILE__), "i" (__LINE__), \ "i" (flags), \ "i" (sizeof(struct bug_entry))); \ } while (0) Align the real size of struct bug_entry through .org. What do you think? >> .popsection; \ >> 14471: >> #else >> -- >> 1.8.5.6 >> >> > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel