Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753382AbdHOQbv (ORCPT ); Tue, 15 Aug 2017 12:31:51 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:54526 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752421AbdHOQbs (ORCPT ); Tue, 15 Aug 2017 12:31:48 -0400 Date: Tue, 15 Aug 2017 17:30:36 +0100 From: Mark Rutland To: Andy Lutomirski Cc: "linux-arm-kernel@lists.infradead.org" , Ard Biesheuvel , Catalin Marinas , James Morse , Laura Abbott , "linux-kernel@vger.kernel.org" , Matt Fleming , Will Deacon , "kernel-hardening@lists.openwall.com" , Kees Cook Subject: Re: [PATCHv2 02/14] fork: allow arch-override of VMAP stack alignment Message-ID: <20170815163036.GJ6090@leverpostej> References: <1502801449-29246-1-git-send-email-mark.rutland@arm.com> <1502801449-29246-3-git-send-email-mark.rutland@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2270 Lines: 66 On Tue, Aug 15, 2017 at 09:09:36AM -0700, Andy Lutomirski wrote: > On Tue, Aug 15, 2017 at 5:50 AM, Mark Rutland wrote: > > In some cases, an architecture might wish its stacks to be aligned to a > > boundary larger than THREAD_SIZE. For example, using an alignment of > > double THREAD_SIZE can allow for stack overflows smaller than > > THREAD_SIZE to be detected by checking a single bit of the stack > > pointer. > > > > This patch allows architectures to override the alignment of VMAP'd > > stacks, by defining THREAD_ALIGN. Where not defined, this defaults to > > THREAD_SIZE, as is the case today. > > This looks okay, but it might make sense to move that to a header file > so THREAD_ALIGN is always available. I was a little worried about breaking things, since arches don't define THREAD_SIZE in a consistent location. Looking again, it looks like those are all transitiviely included into each arch's , so I think I can move this into , which'll have to be added to kernel.fork.c's includes. Are you happy with the below fixup? Thanks, Mark. ---->8---- diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index 250a276..905d769 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -38,6 +38,10 @@ enum { #ifdef __KERNEL__ +#ifndef THREAD_ALIGN +#define THREAD_ALIGN THREAD_SIZE +#endif + #ifdef CONFIG_DEBUG_STACK_USAGE # define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_NOTRACK | \ __GFP_ZERO) diff --git a/kernel/fork.c b/kernel/fork.c index 696d692..f12882a 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -88,6 +88,7 @@ #include #include #include +#include #include #include @@ -217,9 +218,6 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) return s->addr; } -#ifndef THREAD_ALIGN -#define THREAD_ALIGN THREAD_SIZE -#endif stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN, VMALLOC_START, VMALLOC_END, THREADINFO_GFP,