From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752096AbeDPP4k (ORCPT ); Mon, 16 Apr 2018 11:56:40 -0400 Received: from mail.kmu-office.ch ([178.209.48.109]:42010 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751169AbeDPP4i (ORCPT ); Mon, 16 Apr 2018 11:56:38 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Date: Mon, 16 Apr 2018 17:56:34 +0200 From: Stefan Agner To: Stephen Warren Cc: Robin Murphy , linux@armlinux.org.uk, ard.biesheuvel@linaro.org, arnd@arndb.de, nicolas.pitre@linaro.org, marc.zyngier@arm.com, behanw@converseincode.com, keescook@chromium.org, Bernhard.Rosenkranzer@linaro.org, mka@chromium.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Thierry Reding , Dmitry Osipenko Subject: Re: [PATCH v2 3/6] ARM: trusted_foundations: do not use naked function In-Reply-To: References: <20180325180959.28008-1-stefan@agner.ch> <20180325180959.28008-4-stefan@agner.ch> <704c863a-0b5a-6396-d7da-f0ed17b7cca2@gmail.com> <263337af-7541-be9e-3db6-6cb987fd08fb@arm.com> Message-ID: User-Agent: Roundcube Webmail/1.3.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 27.03.2018 14:16, Dmitry Osipenko wrote: > On 27.03.2018 14:54, Robin Murphy wrote: >> On 26/03/18 22:20, Dmitry Osipenko wrote: >>> On 25.03.2018 21:09, Stefan Agner wrote: >>>> As documented in GCC naked functions should only use Basic asm >>>> syntax. The Extended asm or mixture of Basic asm and "C" code is >>>> not guaranteed. Currently this works because it was hard coded >>>> to follow and check GCC behavior for arguments and register >>>> placement. >>>> >>>> Furthermore with clang using parameters in Extended asm in a >>>> naked function is not supported: >>>>    arch/arm/firmware/trusted_foundations.c:47:10: error: parameter >>>>            references not allowed in naked functions >>>>                  : "r" (type), "r" (arg1), "r" (arg2) >>>>                         ^ >>>> >>>> Use a regular function to be more portable. This aligns also with >>>> the other smc call implementations e.g. in qcom_scm-32.c and >>>> bcm_kona_smc.c. >>>> >>>> Cc: Dmitry Osipenko >>>> Cc: Stephen Warren >>>> Cc: Thierry Reding >>>> Signed-off-by: Stefan Agner >>>> --- >>>> Changes in v2: >>>> - Keep stmfd/ldmfd to avoid potential ABI issues >>>> >>>>   arch/arm/firmware/trusted_foundations.c | 14 +++++++++----- >>>>   1 file changed, 9 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/arch/arm/firmware/trusted_foundations.c >>>> b/arch/arm/firmware/trusted_foundations.c >>>> index 3fb1b5a1dce9..689e6565abfc 100644 >>>> --- a/arch/arm/firmware/trusted_foundations.c >>>> +++ b/arch/arm/firmware/trusted_foundations.c >>>> @@ -31,21 +31,25 @@ >>>>     static unsigned long cpu_boot_addr; >>>>   -static void __naked tf_generic_smc(u32 type, u32 arg1, u32 arg2) >>>> +static void tf_generic_smc(u32 type, u32 arg1, u32 arg2) >>>>   { >>>> +    register u32 r0 asm("r0") = type; >>>> +    register u32 r1 asm("r1") = arg1; >>>> +    register u32 r2 asm("r2") = arg2; >>>> + >>>>       asm volatile( >>>>           ".arch_extension    sec\n\t" >>>> -        "stmfd    sp!, {r4 - r11, lr}\n\t" >>>> +        "stmfd    sp!, {r4 - r11}\n\t" >>>>           __asmeq("%0", "r0") >>>>           __asmeq("%1", "r1") >>>>           __asmeq("%2", "r2") >>>>           "mov    r3, #0\n\t" >>>>           "mov    r4, #0\n\t" >>>>           "smc    #0\n\t" >>>> -        "ldmfd    sp!, {r4 - r11, pc}" >>>> +        "ldmfd    sp!, {r4 - r11}\n\t" >>>>           : >>>> -        : "r" (type), "r" (arg1), "r" (arg2) >>>> -        : "memory"); >>>> +        : "r" (r0), "r" (r1), "r" (r2) >>>> +        : "memory", "r3", "r12", "lr"); >>> >>> Although seems "lr" won't be affected by SMC invocation because it should be >>> banked and hence could be omitted entirely from the code. Maybe somebody could >>> confirm this. >> Strictly per the letter of the architecture, the SMC could be trapped to Hyp >> mode, and a hypervisor might clobber LR_usr in the process of forwarding the >> call to the firmware secure monitor (since Hyp doesn't have a banked LR of its >> own). Admittedly there are probably no real systems with the appropriate >> hardware/software combination to hit that, but on the other hand if this gets >> inlined where the compiler has already created a stack frame then an LR clobber >> is essentially free, so I reckon we're better off keeping it for reassurance. >> This isn't exactly a critical fast path anyway. > > Okay, thank you for the clarification. So it seems this change is fine? Stephen, you picked up changes for this driver before, is this patch going through your tree? -- Stefan From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefan@agner.ch (Stefan Agner) Date: Mon, 16 Apr 2018 17:56:34 +0200 Subject: [PATCH v2 3/6] ARM: trusted_foundations: do not use naked function In-Reply-To: References: <20180325180959.28008-1-stefan@agner.ch> <20180325180959.28008-4-stefan@agner.ch> <704c863a-0b5a-6396-d7da-f0ed17b7cca2@gmail.com> <263337af-7541-be9e-3db6-6cb987fd08fb@arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 27.03.2018 14:16, Dmitry Osipenko wrote: > On 27.03.2018 14:54, Robin Murphy wrote: >> On 26/03/18 22:20, Dmitry Osipenko wrote: >>> On 25.03.2018 21:09, Stefan Agner wrote: >>>> As documented in GCC naked functions should only use Basic asm >>>> syntax. The Extended asm or mixture of Basic asm and "C" code is >>>> not guaranteed. Currently this works because it was hard coded >>>> to follow and check GCC behavior for arguments and register >>>> placement. >>>> >>>> Furthermore with clang using parameters in Extended asm in a >>>> naked function is not supported: >>>> ?? arch/arm/firmware/trusted_foundations.c:47:10: error: parameter >>>> ?????????? references not allowed in naked functions >>>> ???????????????? : "r" (type), "r" (arg1), "r" (arg2) >>>> ??????????????????????? ^ >>>> >>>> Use a regular function to be more portable. This aligns also with >>>> the other smc call implementations e.g. in qcom_scm-32.c and >>>> bcm_kona_smc.c. >>>> >>>> Cc: Dmitry Osipenko >>>> Cc: Stephen Warren >>>> Cc: Thierry Reding >>>> Signed-off-by: Stefan Agner >>>> --- >>>> Changes in v2: >>>> - Keep stmfd/ldmfd to avoid potential ABI issues >>>> >>>> ? arch/arm/firmware/trusted_foundations.c | 14 +++++++++----- >>>> ? 1 file changed, 9 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/arch/arm/firmware/trusted_foundations.c >>>> b/arch/arm/firmware/trusted_foundations.c >>>> index 3fb1b5a1dce9..689e6565abfc 100644 >>>> --- a/arch/arm/firmware/trusted_foundations.c >>>> +++ b/arch/arm/firmware/trusted_foundations.c >>>> @@ -31,21 +31,25 @@ >>>> ? ? static unsigned long cpu_boot_addr; >>>> ? -static void __naked tf_generic_smc(u32 type, u32 arg1, u32 arg2) >>>> +static void tf_generic_smc(u32 type, u32 arg1, u32 arg2) >>>> ? { >>>> +??? register u32 r0 asm("r0") = type; >>>> +??? register u32 r1 asm("r1") = arg1; >>>> +??? register u32 r2 asm("r2") = arg2; >>>> + >>>> ????? asm volatile( >>>> ????????? ".arch_extension??? sec\n\t" >>>> -??????? "stmfd??? sp!, {r4 - r11, lr}\n\t" >>>> +??????? "stmfd??? sp!, {r4 - r11}\n\t" >>>> ????????? __asmeq("%0", "r0") >>>> ????????? __asmeq("%1", "r1") >>>> ????????? __asmeq("%2", "r2") >>>> ????????? "mov??? r3, #0\n\t" >>>> ????????? "mov??? r4, #0\n\t" >>>> ????????? "smc??? #0\n\t" >>>> -??????? "ldmfd??? sp!, {r4 - r11, pc}" >>>> +??????? "ldmfd??? sp!, {r4 - r11}\n\t" >>>> ????????? : >>>> -??????? : "r" (type), "r" (arg1), "r" (arg2) >>>> -??????? : "memory"); >>>> +??????? : "r" (r0), "r" (r1), "r" (r2) >>>> +??????? : "memory", "r3", "r12", "lr"); >>> >>> Although seems "lr" won't be affected by SMC invocation because it should be >>> banked and hence could be omitted entirely from the code. Maybe somebody could >>> confirm this. >> Strictly per the letter of the architecture, the SMC could be trapped to Hyp >> mode, and a hypervisor might clobber LR_usr in the process of forwarding the >> call to the firmware secure monitor (since Hyp doesn't have a banked LR of its >> own). Admittedly there are probably no real systems with the appropriate >> hardware/software combination to hit that, but on the other hand if this gets >> inlined where the compiler has already created a stack frame then an LR clobber >> is essentially free, so I reckon we're better off keeping it for reassurance. >> This isn't exactly a critical fast path anyway. > > Okay, thank you for the clarification. So it seems this change is fine? Stephen, you picked up changes for this driver before, is this patch going through your tree? -- Stefan