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 49032C4332F for ; Fri, 9 Dec 2022 11:10:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229850AbiLILJ6 (ORCPT ); Fri, 9 Dec 2022 06:09:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39386 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229573AbiLILJw (ORCPT ); Fri, 9 Dec 2022 06:09:52 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 579143AC0A for ; Fri, 9 Dec 2022 03:09:51 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id DA46023A; Fri, 9 Dec 2022 03:09:57 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.39.232]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E52CD3F73B; Fri, 9 Dec 2022 03:09:49 -0800 (PST) Date: Fri, 9 Dec 2022 11:09:47 +0000 From: Mark Rutland To: ruanjinjie Cc: catalin.marinas@arm.com, will@kernel.org, haibinzhang@tencent.com, hewenliang4@huawei.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64: fix a concurrency issue in emulation_proc_handler() Message-ID: References: <20221209105556.47621-1-ruanjinjie@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221209105556.47621-1-ruanjinjie@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 09, 2022 at 06:55:56PM +0800, ruanjinjie wrote: > 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 = INSN_UNDEF and > current_mode = INSN_EMULATE, then call register_emulation_hooks twice, > resulting in a list_add double problem. > > 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 The version queued in the arm64 for-next/core branch no longer has the list manipulation, but we do need to fix this for stable, and there is a remaining race on reading insn->current_mode in emulation_proc_handler(). > Fixes: af483947d472 ("arm64: fix oops in concurrently setting insn_emulation sysctls") > Signed-off-by: ruanjinjie > --- > 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 fb0e7c7b2e20..d33e5d9e6990 100644 > --- a/arch/arm64/kernel/armv8_deprecated.c > +++ b/arch/arm64/kernel/armv8_deprecated.c > @@ -208,10 +208,12 @@ static int emulation_proc_handler(struct ctl_table *table, int write, > loff_t *ppos) > { > int ret = 0; > - struct insn_emulation *insn = container_of(table->data, struct insn_emulation, current_mode); > - enum insn_emulation_mode prev_mode = insn->current_mode; > + struct insn_emulation *insn; > + enum insn_emulation_mode prev_mode; > > mutex_lock(&insn_emulation_mutex); > + insn = container_of(table->data, struct insn_emulation, current_mode); > + prev_mode = insn->current_mode; > ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); We don't strictly need to move the container_of(), but it makes no odds either way, and this looks good to me: Acked-by: Mark Rutland Mark. > > if (ret || !write || prev_mode == insn->current_mode) > -- > 2.25.1 >