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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 7FD53C352AA for ; Tue, 1 Oct 2019 10:33:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5C9452190F for ; Tue, 1 Oct 2019 10:33:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731088AbfJAKdY (ORCPT ); Tue, 1 Oct 2019 06:33:24 -0400 Received: from foss.arm.com ([217.140.110.172]:46278 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729675AbfJAKdY (ORCPT ); Tue, 1 Oct 2019 06:33:24 -0400 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 81F3A1000; Tue, 1 Oct 2019 03:33:23 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7E8923F739; Tue, 1 Oct 2019 03:33:22 -0700 (PDT) Date: Tue, 1 Oct 2019 11:33:20 +0100 From: Dave Martin To: Masayoshi Mizuma Cc: Julien Grall , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, Masayoshi Mizuma , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] arm64/sve: Fix wrong free for task->thread.sve_state Message-ID: <20191001103317.GV27757@arm.com> References: <20190930205600.25542-1-msys.mizuma@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190930205600.25542-1-msys.mizuma@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 30, 2019 at 04:56:00PM -0400, Masayoshi Mizuma wrote: > From: Masayoshi Mizuma > > The system which has SVE feature crashed because of > the memory pointed by task->thread.sve_state was destroyed > by someone. > > That is because sve_state is freed while the forking the > child process. The child process has the pointer of sve_state > which is same as the parent's because the child's task_struct > is copied from the parent's one. If the copy_process() > fails as an error on somewhere, for example, copy_creds(), > then the sve_state is freed even if the parent is alive. > The flow is as follows. > > copy_process > p = dup_task_struct > => arch_dup_task_struct > *dst = *src; // copy the entire region. > : > retval = copy_creds > if (retval < 0) > goto bad_fork_free; > : > bad_fork_free: > ... > delayed_free_task(p); > => free_task > => arch_release_task_struct > => fpsimd_release_task > => __sve_free > => kfree(task->thread.sve_state); > // free the parent's sve_state > > Move child's sve_state = NULL and clearing TIF_SVE flag > to arch_dup_task_struct() so that the child doesn't free the > parent's one. > There is no need to wait until copy_process() to clear TIF_SVE for > dst, because the thread flags for dst are initialized already by > copying the src task_struct. > This change simplifies the code, so get rid of comments that are no > longer needed. > > As a note, arm64 used to have thread_info on the stack. So it > would not be possible to clear TIF_SVE until the stack is initialized. > From commit c02433dd6de3 ("arm64: split thread_info from task stack"), > the thread_info is part of the task, so it should be valid to modify > the flag from arch_dup_task_struct(). > > Cc: stable@vger.kernel.org # 4.15.x- > Fixes: bc0ee4760364 ("arm64/sve: Core task context handling") > Signed-off-by: Masayoshi Mizuma > Reported-by: Hidetoshi Seto > Suggested-by: Dave Martin > Tested-by: Julien Grall Looks OK to me: Reviewed-by: Dave Martin Cheers ---Dave > --- > arch/arm64/kernel/process.c | 32 +++++++++++++++----------------- > 1 file changed, 15 insertions(+), 17 deletions(-) > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index a47462def04b..ef7aa909bfda 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -332,22 +332,27 @@ void arch_release_task_struct(struct task_struct *tsk) > fpsimd_release_task(tsk); > } > > -/* > - * src and dst may temporarily have aliased sve_state after task_struct > - * is copied. We cannot fix this properly here, because src may have > - * live SVE state and dst's thread_info may not exist yet, so tweaking > - * either src's or dst's TIF_SVE is not safe. > - * > - * The unaliasing is done in copy_thread() instead. This works because > - * dst is not schedulable or traceable until both of these functions > - * have been called. > - */ > int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) > { > if (current->mm) > fpsimd_preserve_current_state(); > *dst = *src; > > + /* We rely on the above assignment to initialize dst's thread_flags: */ > + BUILD_BUG_ON(!IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK)); > + > + /* > + * Detach src's sve_state (if any) from dst so that it does not > + * get erroneously used or freed prematurely. dst's sve_state > + * will be allocated on demand later on if dst uses SVE. > + * For consistency, also clear TIF_SVE here: this could be done > + * later in copy_process(), but to avoid tripping up future > + * maintainers it is best not to leave TIF_SVE and sve_state in > + * an inconsistent state, even temporarily. > + */ > + dst->thread.sve_state = NULL; > + clear_tsk_thread_flag(dst, TIF_SVE); > + > return 0; > } > > @@ -360,13 +365,6 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, > > memset(&p->thread.cpu_context, 0, sizeof(struct cpu_context)); > > - /* > - * Unalias p->thread.sve_state (if any) from the parent task > - * and disable discard SVE state for p: > - */ > - clear_tsk_thread_flag(p, TIF_SVE); > - p->thread.sve_state = NULL; > - > /* > * In case p was allocated the same task_struct pointer as some > * other recently-exited task, make sure p is disassociated from > -- > 2.18.1 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel