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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 8DAA0C4360C for ; Fri, 27 Sep 2019 12:52:45 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4777A20872 for ; Fri, 27 Sep 2019 12:52:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="By927+WV" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4777A20872 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=u+1HSBqge6iicuuvuo6RQnydSylX7rQlDi6kJOo9o48=; b=By927+WV/C+gnm UScMHykW5ZAkE/lAEElyZZsZVduqvWIsWPRivSWyxsJyzqOZBcdGrmKcWY/9AY7gL7yPHFeedaSHr gi6/HUQPQ9Trj4bcTdoxew5CkZBYIJXvIgpEW6fpp4ivBVPBY4I624xdDgdRuG8fDp9xmBMXv5NfS EMtJo/QqXlxT2OcruWU2U5ycHUDPXSCC66ZWuIprTtIOrmpQdp2jek+y5qHvDnKSwQFW3rHGsElFu wSjgeOVoMXOM7MOGBc8mg80gQNwzwWSK9Jj4IO5R2xHELfMBCcgjmHTLrbFJXeq7YflDptHKExwQj S81j1uH6DyzVL+d9D1kw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1iDpjj-0006CG-VG; Fri, 27 Sep 2019 12:52:39 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.2 #3 (Red Hat Linux)) id 1iDpjg-0006B6-Ao for linux-arm-kernel@lists.infradead.org; Fri, 27 Sep 2019 12:52:38 +0000 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 9E7231000; Fri, 27 Sep 2019 05:52:33 -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 9A8853F67D; Fri, 27 Sep 2019 05:52:32 -0700 (PDT) Date: Fri, 27 Sep 2019 13:52:30 +0100 From: Dave Martin To: Masayoshi Mizuma Subject: Re: [PATCH 1/1] arm64/sve: Fix wrong free for task->thread.sve_state Message-ID: <20190927125228.GQ27757@arm.com> References: <20190926190846.3072-1-msys.mizuma@gmail.com> <20190926190846.3072-2-msys.mizuma@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190926190846.3072-2-msys.mizuma@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190927_055236_520254_73842F9E X-CRM114-Status: GOOD ( 26.59 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Masayoshi Mizuma , Catalin Marinas , linux-kernel@vger.kernel.org, Julien Grall , Will Deacon , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Sep 26, 2019 at 03:08:46PM -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 > > 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. > > 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; There's definitely a problem here, but a simpler fix is probably to NULL sve_state and clear TIF_SVE for dst at the same time. Once upon a time, I had to cope with the thread_flags not being copied as part of task_struct here, which is one reason why the code is the (broken) way it is, but this is ancient history... Commit c02433dd6de3 ("arm64: split thread_info from task stack") was merged in v4.10 and predates SVE support anyway. So can just do the following (untested) and delete the confusing comments? Cheers ---Dave --8<-- diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index f674f28..6937f59 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -323,22 +323,16 @@ 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; + BUILD_BUG_ON(!IS_ENABLED(CONFIG_THREAD_INFO_IN_TASK)); + dst->thread.sve_state = NULL; + clear_tsk_thread_flag(dst, TIF_SVE); + return 0; } @@ -352,13 +346,6 @@ 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 * any cpu that may have run that now-exited task recently. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel