From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:60578 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754872AbdK1Kmu (ORCPT ); Tue, 28 Nov 2017 05:42:50 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Christian Borntraeger , Heiko Carstens , Martin Schwidefsky Subject: [PATCH 4.14 004/193] s390/guarded storage: fix possible memory corruption Date: Tue, 28 Nov 2017 11:24:11 +0100 Message-Id: <20171128100613.843756756@linuxfoundation.org> In-Reply-To: <20171128100613.638270407@linuxfoundation.org> References: <20171128100613.638270407@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Heiko Carstens commit fa1edf3f63c05ca8eacafcd7048ed91e5360f1a8 upstream. For PREEMPT enabled kernels the guarded storage (GS) code contains a possible use-after-free bug. If a task that makes use of GS exits, it will execute do_exit() while still enabled for preemption. That function will call exit_thread_runtime_instr() via exit_thread(). If exit_thread_gs() gets preempted after the GS control block of the task has been freed but before the pointer to it is set to NULL, then save_gs_cb(), called from switch_to(), will write to already freed memory. Avoid this and simply disable preemption while freeing the control block and setting the pointer to NULL. Fixes: 916cda1aa1b4 ("s390: add a system call for guarded storage") Reviewed-by: Christian Borntraeger Signed-off-by: Heiko Carstens Signed-off-by: Martin Schwidefsky Signed-off-by: Greg Kroah-Hartman --- arch/s390/kernel/guarded_storage.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/s390/kernel/guarded_storage.c +++ b/arch/s390/kernel/guarded_storage.c @@ -14,9 +14,11 @@ void exit_thread_gs(void) { + preempt_disable(); kfree(current->thread.gs_cb); kfree(current->thread.gs_bc_cb); current->thread.gs_cb = current->thread.gs_bc_cb = NULL; + preempt_enable(); } static int gs_enable(void)