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 X-Spam-Level: X-Spam-Status: No, score=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D464BC433E0 for ; Wed, 17 Mar 2021 18:13:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 527A564E31 for ; Wed, 17 Mar 2021 18:13:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233053AbhCQSNg (ORCPT ); Wed, 17 Mar 2021 14:13:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:48374 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232951AbhCQSM5 (ORCPT ); Wed, 17 Mar 2021 14:12:57 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id DA0AC64F51; Wed, 17 Mar 2021 18:12:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1616004777; bh=YNYfkgvTFAj03+n7BwXKskQ9kiTkKnyGG+hw6GogYSM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UCN51gHzfJJCl6MlZL8qhrf8OO3AibT5jEE4Dc1ubp7X7oknrp5Nj7XVHWNmHG6Sj r1BbliCI2JKHtd8KPwg8uXb7qptmxDvoP588HfSX1roaI4t1H6A2/T8g4zmk8AkTGi CSl/BoouW8nLXK4Wz6rW7SWgtzBGPBxLDDGFkQ9nSyk0GlA+Pg8/FlWJyNQq+VTYLn AbLzlgcoWI/jEoxD6IHd/Y46QfT+ZerBt+T/OcOTyD82Epxdbk60weHYepTHCncEAH NB4L/aA7F5gqAP0b/8kBV8wOGZdqi0uklgUpd2p/cTwe6DQePKeUJ0jyXj9S6apKxT wVX3R0BNx4JYQ== From: Andy Lutomirski To: x86@kernel.org Cc: LKML , Mark Rutland , Brian Gerst , Andy Lutomirski Subject: [PATCH v4 8/9] kentry: Check that syscall entries and syscall exits match Date: Wed, 17 Mar 2021 11:12:47 -0700 Message-Id: <4198487ed07d3e21da48d1884e7cddadf6efa928.1616004689.git.luto@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If arch code calls the wrong kernel entry helpers, syscall entries and exits can get out of sync. Add a new field to task_struct to track the syscall state and validate that it transitions correctly. Signed-off-by: Andy Lutomirski --- include/linux/sched.h | 4 ++++ init/init_task.c | 8 ++++++++ kernel/entry/common.c | 24 +++++++++++++++++++++++- 3 files changed, 35 insertions(+), 1 deletion(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 6e3a5eeec509..95d6d8686d98 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1368,6 +1368,10 @@ struct task_struct { struct llist_head kretprobe_instances; #endif +#ifdef CONFIG_DEBUG_ENTRY + bool kentry_in_syscall; +#endif + /* * New fields for task_struct should be added above here, so that * they are included in the randomized portion of task_struct. diff --git a/init/init_task.c b/init/init_task.c index 8a992d73e6fb..de4fdaac4e8b 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -212,6 +212,14 @@ struct task_struct init_task #ifdef CONFIG_SECCOMP .seccomp = { .filter_count = ATOMIC_INIT(0) }, #endif +#ifdef CONFIG_DEBUG_ENTRY + /* + * The init task, and kernel threads in general, are considered + * to be "in a syscall". This way they can execve() and then exit + * the supposed syscall that they were in to go to user mode. + */ + .kentry_in_syscall = true, +#endif }; EXPORT_SYMBOL(init_task); diff --git a/kernel/entry/common.c b/kernel/entry/common.c index 8ba774184e00..152e7546be16 100644 --- a/kernel/entry/common.c +++ b/kernel/entry/common.c @@ -141,11 +141,21 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall, long kentry_syscall_begin(struct pt_regs *regs, long syscall) { - unsigned long work = READ_ONCE(current_thread_info()->syscall_work); + unsigned long work; + + if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) { + DEBUG_ENTRY_WARN_ONCE( + current->kentry_in_syscall, + "entering syscall %ld while already in a syscall", + syscall); + current->kentry_in_syscall = true; + } CT_WARN_ON(ct_state() != CONTEXT_KERNEL); lockdep_assert_irqs_enabled(); + work = READ_ONCE(current_thread_info()->syscall_work); + if (work & SYSCALL_WORK_ENTER) syscall = syscall_trace_enter(regs, syscall, work); @@ -156,11 +166,16 @@ long kentry_syscall_begin(struct pt_regs *regs, long syscall) static __always_inline void __exit_to_user_mode(void) { instrumentation_begin(); + #ifdef CONFIG_DEBUG_ENTRY DEBUG_ENTRY_WARN_ONCE(this_cpu_read(kentry_cpu_depth) != 1, "__exit_to_user_mode called at wrong kentry cpu depth (%u)", this_cpu_read(kentry_cpu_depth)); + + DEBUG_ENTRY_WARN_ONCE(current->kentry_in_syscall, + "exiting to user mode while in syscall context"); #endif + trace_hardirqs_on_prepare(); lockdep_hardirqs_on_prepare(CALLER_ADDR0); instrumentation_end(); @@ -317,6 +332,13 @@ void kentry_syscall_end(struct pt_regs *regs) */ if (unlikely(work & SYSCALL_WORK_EXIT)) syscall_exit_work(regs, work); + +#ifdef CONFIG_DEBUG_ENTRY + DEBUG_ENTRY_WARN_ONCE(!current->kentry_in_syscall, + "exiting syscall %lu without entering first", nr); + + current->kentry_in_syscall = 0; +#endif } noinstr void kentry_enter_from_user_mode(struct pt_regs *regs) -- 2.30.2