From nobody Mon Dec 15 21:29:08 2025 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 A057AC4332F for ; Mon, 30 Oct 2023 06:38:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231656AbjJ3GiI (ORCPT ); Mon, 30 Oct 2023 02:38:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60816 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231678AbjJ3GiG (ORCPT ); Mon, 30 Oct 2023 02:38:06 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7437DAB for ; Sun, 29 Oct 2023 23:37:56 -0700 (PDT) Received: from kwepemi500008.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4SJk3X2WFqzvQJ0; Mon, 30 Oct 2023 14:32:56 +0800 (CST) Received: from huawei.com (10.67.174.55) by kwepemi500008.china.huawei.com (7.221.188.139) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.31; Mon, 30 Oct 2023 14:37:53 +0800 From: Jinjie Ruan To: , , , , , CC: Subject: [PATCH v4.19] arm64: fix a concurrency issue in emulation_proc_handler() Date: Mon, 30 Oct 2023 06:37:09 +0000 Message-ID: <20231030063709.2443546-1-ruanjinjie@huawei.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.67.174.55] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemi500008.china.huawei.com (7.221.188.139) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" In linux-6.1, the related code is refactored in commit 124c49b1b5d9 ("arm64: armv8_deprecated: rework deprected instruction handling") and this issue was incidentally fixed. I have adapted the patch set to linux stable 5.10. However, 4.19 and 5.10 are too different and the patch set is hard to adapt to 4.19. This patch is to solve the problem of repeated addition of linked lists described below with few changes. How to reproduce: CONFIG_ARMV8_DEPRECATED=3Dy, CONFIG_SWP_EMULATION=3Dy, and CONFIG_DEBUG_LIS= T=3Dy, then launch two shell executions: #!/bin/bash while [ 1 ]; do echo 1 > /proc/sys/abi/swp done or "echo 1 > /proc/sys/abi/swp" and then aunch two shell executions: #!/bin/bash while [ 1 ]; do echo 0 > /proc/sys/abi/swp done In emulation_proc_handler(), read and write operations are performed on insn->current_mode. In the concurrency scenario, mutex only protects writing insn->current_mode, and not protects the read. Suppose there are two concurrent tasks, task1 updates insn->current_mode to INSN_EMULATE in the critical section, the prev_mode of task2 is still the old data INSN_UNDEF of insn->current_mode. As a result, two tasks call update_insn_emulation_mode twice with prev_mode =3D INSN_UNDEF and current_mode =3D INSN_EMULATE, then call register_emulation_hooks twice, resulting in a list_add double problem. After applying this patch, the following list add or list del double warnings never occur. Call trace: __list_add_valid+0xd8/0xe4 register_undef_hook+0x94/0x13c update_insn_emulation_mode+0xd0/0x12c emulation_proc_handler+0xd8/0xf4 proc_sys_call_handler+0x140/0x250 proc_sys_write+0x1c/0x2c new_sync_write+0xec/0x18c vfs_write+0x214/0x2ac ksys_write+0x70/0xfc __arm64_sys_write+0x24/0x30 el0_svc_common.constprop.0+0x7c/0x1bc do_el0_svc+0x2c/0x94 el0_svc+0x20/0x30 el0_sync_handler+0xb0/0xb4 el0_sync+0x160/0x180 Call trace: __list_del_entry_valid+0xac/0x110 unregister_undef_hook+0x34/0x80 update_insn_emulation_mode+0xf0/0x180 emulation_proc_handler+0x8c/0xd8 proc_sys_call_handler+0x1d8/0x208 proc_sys_write+0x14/0x20 new_sync_write+0xf0/0x190 vfs_write+0x304/0x388 ksys_write+0x6c/0x100 __arm64_sys_write+0x1c/0x28 el0_svc_common.constprop.4+0x68/0x188 do_el0_svc+0x24/0xa0 el0_svc+0x14/0x20 el0_sync_handler+0x90/0xb8 el0_sync+0x160/0x180 Fixes: af483947d472 ("arm64: fix oops in concurrently setting insn_emulatio= n sysctls") Cc: stable@vger.kernel.org#4.19.x Cc: gregkh@linuxfoundation.org Signed-off-by: Jinjie Ruan Acked-by: Mark Rutland --- arch/arm64/kernel/armv8_deprecated.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8= _deprecated.c index 7c69a203cdf8..b8d481c3e26d 100644 --- a/arch/arm64/kernel/armv8_deprecated.c +++ b/arch/arm64/kernel/armv8_deprecated.c @@ -211,10 +211,12 @@ static int emulation_proc_handler(struct ctl_table *t= able, int write, loff_t *ppos) { int ret =3D 0; - struct insn_emulation *insn =3D container_of(table->data, struct insn_emu= lation, current_mode); - enum insn_emulation_mode prev_mode =3D insn->current_mode; + struct insn_emulation *insn; + enum insn_emulation_mode prev_mode; =20 mutex_lock(&insn_emulation_mutex); + insn =3D container_of(table->data, struct insn_emulation, current_mode); + prev_mode =3D insn->current_mode; ret =3D proc_dointvec_minmax(table, write, buffer, lenp, ppos); =20 if (ret || !write || prev_mode =3D=3D insn->current_mode) --=20 2.34.1