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[2620:137:e000::1:20]) by mx.google.com with ESMTP id he14-20020a1709073d8e00b0078df1c345e4si30035170ejc.518.2022.10.24.05.15.36; Mon, 24 Oct 2022 05:16:00 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linuxfoundation.org header.s=korg header.b=05O7N2Ip; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linuxfoundation.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232729AbiJXMHM (ORCPT + 99 others); Mon, 24 Oct 2022 08:07:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39060 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232937AbiJXMEk (ORCPT ); Mon, 24 Oct 2022 08:04:40 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 163627CB65; Mon, 24 Oct 2022 04:51:02 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 96FEFB811B3; Mon, 24 Oct 2022 11:49:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02D9AC433C1; Mon, 24 Oct 2022 11:49:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666612189; bh=xIiHCK+1tURwLFmjhuDlO4CmC1NAr2veG4MABKBnho8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=05O7N2IpZ9LzdpZ+i0zELa3a3at4tNWTrucS5utuUJ0axhz+99mZMYzb/uSJi/4V4 gt0kvXZM7iDqxaMAWuFfsgWlTnz/8IQct/IONr7aUcE49HjpKak6/d7/vGO0xJmaux nQxhbI9Upjc3EJ13pJWvoMd111yHt1empZXoMXMY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Rik van Riel , Breno Leitao , Petr Mladek , Josh Poimboeuf , stable@kernel.org Subject: [PATCH 4.14 072/210] livepatch: fix race between fork and KLP transition Date: Mon, 24 Oct 2022 13:29:49 +0200 Message-Id: <20221024112959.400039448@linuxfoundation.org> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20221024112956.797777597@linuxfoundation.org> References: <20221024112956.797777597@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 X-Spam-Status: No, score=-7.6 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_HI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1747571190873168826?= X-GMAIL-MSGID: =?utf-8?q?1747571190873168826?= From: Rik van Riel commit 747f7a2901174c9afa805dddfb7b24db6f65e985 upstream. The KLP transition code depends on the TIF_PATCH_PENDING and the task->patch_state to stay in sync. On a normal (forward) transition, TIF_PATCH_PENDING will be set on every task in the system, while on a reverse transition (after a failed forward one) first TIF_PATCH_PENDING will be cleared from every task, followed by it being set on tasks that need to be transitioned back to the original code. However, the fork code copies over the TIF_PATCH_PENDING flag from the parent to the child early on, in dup_task_struct and setup_thread_stack. Much later, klp_copy_process will set child->patch_state to match that of the parent. However, the parent's patch_state may have been changed by KLP loading or unloading since it was initially copied over into the child. This results in the KLP code occasionally hitting this warning in klp_complete_transition: for_each_process_thread(g, task) { WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING)); task->patch_state = KLP_UNDEFINED; } Set, or clear, the TIF_PATCH_PENDING flag in the child task depending on whether or not it is needed at the time klp_copy_process is called, at a point in copy_process where the tasklist_lock is held exclusively, preventing races with the KLP code. The KLP code does have a few places where the state is changed without the tasklist_lock held, but those should not cause problems because klp_update_patch_state(current) cannot be called while the current task is in the middle of fork, klp_check_and_switch_task() which is called under the pi_lock, which prevents rescheduling, and manipulation of the patch state of idle tasks, which do not fork. This should prevent this warning from triggering again in the future, and close the race for both normal and reverse transitions. Signed-off-by: Rik van Riel Reported-by: Breno Leitao Reviewed-by: Petr Mladek Acked-by: Josh Poimboeuf Fixes: d83a7cb375ee ("livepatch: change to a per-task consistency model") Cc: stable@kernel.org Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20220808150019.03d6a67b@imladris.surriel.com Signed-off-by: Greg Kroah-Hartman --- kernel/livepatch/transition.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) --- a/kernel/livepatch/transition.c +++ b/kernel/livepatch/transition.c @@ -573,7 +573,21 @@ void klp_reverse_transition(void) /* Called from copy_process() during fork */ void klp_copy_process(struct task_struct *child) { - child->patch_state = current->patch_state; - /* TIF_PATCH_PENDING gets copied in setup_thread_stack() */ + /* + * The parent process may have gone through a KLP transition since + * the thread flag was copied in setup_thread_stack earlier. Bring + * the task flag up to date with the parent here. + * + * The operation is serialized against all klp_*_transition() + * operations by the tasklist_lock. The only exception is + * klp_update_patch_state(current), but we cannot race with + * that because we are current. + */ + if (test_tsk_thread_flag(current, TIF_PATCH_PENDING)) + set_tsk_thread_flag(child, TIF_PATCH_PENDING); + else + clear_tsk_thread_flag(child, TIF_PATCH_PENDING); + + child->patch_state = current->patch_state; }