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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 C43DFC4360C for ; Fri, 27 Sep 2019 11:04:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9E1A5217F4 for ; Fri, 27 Sep 2019 11:04:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726796AbfI0LEk (ORCPT ); Fri, 27 Sep 2019 07:04:40 -0400 Received: from foss.arm.com ([217.140.110.172]:49192 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725882AbfI0LEk (ORCPT ); Fri, 27 Sep 2019 07:04:40 -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 9EA0928; Fri, 27 Sep 2019 04:04:39 -0700 (PDT) Received: from [10.1.196.50] (e108454-lin.cambridge.arm.com [10.1.196.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AFD8C3F67D; Fri, 27 Sep 2019 04:04:38 -0700 (PDT) Subject: Re: [PATCH 1/1] arm64/sve: Fix wrong free for task->thread.sve_state To: Masayoshi Mizuma , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org Cc: Masayoshi Mizuma , linux-kernel@vger.kernel.org, Dave P Martin References: <20190926190846.3072-1-msys.mizuma@gmail.com> <20190926190846.3072-2-msys.mizuma@gmail.com> From: Julien Grall Message-ID: <32b59c08-cc59-60d6-16c7-ffb5582c2901@arm.com> Date: Fri, 27 Sep 2019 12:04:37 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20190926190846.3072-2-msys.mizuma@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (+ Dave) Hi, Thank you for the patch. On 26/09/2019 20:08, 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 The flow makes sense to me and I agree you would end up to free the parent's state. > > Add a flag in task->thread which shows the fork is in progress. > If the fork is in progress, that means the child has the pointer > to the parent's sve_state, doesn't free the sve_state. I haven't fully investigate it yet but I was wondering if we could just clear task->thread.sve_state for the child in arch_dup_task_struct(). I saw the comment on top of function mentioning potential issue to do it there. I understand that you may not be able to clear TIF_SVE in the function, but I don't understand why clearing just task->thread.sve_state would be an issue. The only risk I can see is TIF_SVE may be set with task->thread.sve_state to be NULL. But this is a new task, so I don't think there are risk here to have it unsync. Dave? > > Signed-off-by: Masayoshi Mizuma > Reported-by: Hidetoshi Seto > --- > arch/arm64/include/asm/processor.h | 1 + > arch/arm64/kernel/fpsimd.c | 6 ++++-- > arch/arm64/kernel/process.c | 2 ++ > 3 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index 5623685c7d13..3ca3e350145a 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -143,6 +143,7 @@ struct thread_struct { > unsigned long fault_address; /* fault info */ > unsigned long fault_code; /* ESR_EL1 value */ > struct debug_info debug; /* debugging */ > + unsigned int fork_in_progress; > #ifdef CONFIG_ARM64_PTR_AUTH > struct ptrauth_keys keys_user; > #endif > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > index 37d3912cfe06..8641db4cb062 100644 > --- a/arch/arm64/kernel/fpsimd.c > +++ b/arch/arm64/kernel/fpsimd.c > @@ -202,8 +202,10 @@ static bool have_cpu_fpsimd_context(void) > */ > static void __sve_free(struct task_struct *task) > { > - kfree(task->thread.sve_state); > - task->thread.sve_state = NULL; > + if (!task->thread.fork_in_progress) { > + kfree(task->thread.sve_state); > + task->thread.sve_state = NULL; > + } > } > > static void sve_free(struct task_struct *task) > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > index a47462def04b..8ac0ee4e5f76 100644 > --- a/arch/arm64/kernel/process.c > +++ b/arch/arm64/kernel/process.c > @@ -347,6 +347,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) > if (current->mm) > fpsimd_preserve_current_state(); > *dst = *src; > + dst->thread.fork_in_progress = 1; > > return 0; > } > @@ -365,6 +366,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start, > * and disable discard SVE state for p: > */ > clear_tsk_thread_flag(p, TIF_SVE); > + p->thread.fork_in_progress = 0; > p->thread.sve_state = NULL; > > /* > Cheers, -- Julien Grall