Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755915AbdDFTgX (ORCPT ); Thu, 6 Apr 2017 15:36:23 -0400 Received: from lelnx194.ext.ti.com ([198.47.27.80]:25514 "EHLO lelnx194.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751266AbdDFTgN (ORCPT ); Thu, 6 Apr 2017 15:36:13 -0400 Subject: Re: [PATCH] misc: sram-exec: Use aligned fncpy instead of memcpy To: Russell King - ARM Linux References: <20170405192120.1009-1-d-gerlach@ti.com> <20170406190747.GP23750@n2100.armlinux.org.uk> <9a970ac7-cb8f-28f4-3b84-ad8bedf1242c@ti.com> <20170406192954.GQ23750@n2100.armlinux.org.uk> CC: Greg Kroah-Hartman , Arnd Bergmann , Tony Lindgren , , , , Shawn Guo , Alexandre Belloni , Keerthy J From: Dave Gerlach Message-ID: <67706a7c-506f-a56a-9f57-874d97961fa0@ti.com> Date: Thu, 6 Apr 2017 14:35:29 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <20170406192954.GQ23750@n2100.armlinux.org.uk> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [128.247.83.19] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3632 Lines: 97 On 04/06/2017 02:29 PM, Russell King - ARM Linux wrote: > On Thu, Apr 06, 2017 at 02:14:12PM -0500, Dave Gerlach wrote: >> On 04/06/2017 02:07 PM, Russell King - ARM Linux wrote: >>> On Wed, Apr 05, 2017 at 02:22:33PM -0500, Dave Gerlach wrote: >>>> Russell, >>>> On 04/05/2017 02:21 PM, Dave Gerlach wrote: >>>>> Currently the sram-exec functionality, which allows allocation of >>>>> executable memory and provides an API to move code to it, is only >>>>> selected in configs for the ARM architecture. Based on commit >>>>> 5756e9dd0de6 ("ARM: 6640/1: Thumb-2: Symbol manipulation macros for >>>>> function body copying") simply copying a C function pointer address >>>>> using memcpy without consideration of alignment and Thumb is unsafe on >>>>> ARM platforms. >>>>> >>>>> The aforementioned patch introduces the fncpy macro which is a safe way >>>>> to copy executable code on ARM platforms, so let's make use of that here >>>>> rather than the unsafe plain memcpy that was previously used by >>>>> sram_exec_copy. >>>>> >>>>> In the future, architectures hoping to make use of the sram-exec >>>>> functionality must define an fncpy macro just as ARM has done to >>>>> guarantee or check for safe copying to executable memory before allowing >>>>> the arch to select CONFIG_SRAM_EXEC. >>>>> >>>>> Signed-off-by: Dave Gerlach >>>>> --- >>>>> drivers/misc/sram-exec.c | 3 ++- >>>>> 1 file changed, 2 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/drivers/misc/sram-exec.c b/drivers/misc/sram-exec.c >>>>> index ac522417c462..0057eabe5c03 100644 >>>>> --- a/drivers/misc/sram-exec.c >>>>> +++ b/drivers/misc/sram-exec.c >>>>> @@ -19,6 +19,7 @@ >>>>> #include >>>>> >>>>> #include >>>>> +#include >>>>> >>>>> #include "sram.h" >>>>> >>>>> @@ -93,7 +94,7 @@ int sram_exec_copy(struct gen_pool *pool, void *dst, void *src, >>>>> set_memory_nx((unsigned long)base, pages); >>>>> set_memory_rw((unsigned long)base, pages); >>>>> >>>>> - memcpy(dst, src, size); >>>>> + fncpy(dst, src, size); >>>>> >>>>> set_memory_ro((unsigned long)base, pages); >>>>> set_memory_x((unsigned long)base, pages); >>>>> >>>> >>>> Does this address your concerns from here [1]? Because the only user of this >>>> code is ARM right now I already only build the sram-exec code in if >>>> CONFIG_ARM is selected. >>> >>> Sorry, it does not. Please read the comments in asm/fncpy.h. >>> >>> Deviating from the proscribed usage means your code is, quite simply, >>> buggy. There's no two ways about that. >>> >> >> I understand there are many constraints to using fncpy, as this is what we >> used before to copy our executable code. Apart from users being aware of >> what these constraints are (8-byte aligned, position independent) and making >> sure the code they are moving meets them, are you saying we need some sort >> of additional strict enforcement of them? Because fncpy today will throw a >> bug if you fail to align src and dst properly, so adding another check will >> just double the messages to the user. > > Yes, fncpy() will throw a bug, but as I've already explained: > > sram = alloc(); > > sram_func = fncpy(sram, func, func_size); > > sram_func(); > > is the _only_ valid usage. > > You must not do: > > sram = alloc(); > > fncpy(sram, func, func_size); > > sram(); > > because that will not work with Thumb code. The only permitted usage > is as per the first example above, everything else is buggy. > I see exactly what you mean now. I missed that before, thank you for clarifying. Will update this patch and send a new version. Regards, Dave