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Thu, 12 Jul 2018 15:43:11 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a25:5f51:0:0:0:0:0 with HTTP; Thu, 12 Jul 2018 15:43:10 -0700 (PDT) In-Reply-To: <20180417081109.GA5804@ulmo> 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> <498de826-6e6c-63d8-00d6-f394b2725a34@wwwdotorg.org> <507a66ab9ab530a6d71db7a74f11ddfb@agner.ch> <20180417081109.GA5804@ulmo> From: Kees Cook Date: Thu, 12 Jul 2018 15:43:10 -0700 X-Google-Sender-Auth: vew_1dR0ANp6gc6eMrUYyx6K8bU Message-ID: Subject: Re: [PATCH v2 3/6] ARM: trusted_foundations: do not use naked function To: Thierry Reding Cc: Stefan Agner , Russell King , Stephen Warren , Stephen Warren , Robin Murphy , Ard Biesheuvel , Arnd Bergmann , Nicolas Pitre , Marc Zyngier , Behan Webster , =?UTF-8?Q?Bero_Rosenkr=C3=A4nzer?= , Matthias Kaehlcke , linux-arm-kernel , LKML , Dmitry Osipenko Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 17, 2018 at 1:11 AM, Thierry Reding wrote: > On Mon, Apr 16, 2018 at 08:21:09PM +0200, Stefan Agner wrote: >> On 16.04.2018 18:08, Stephen Warren wrote: >> > On 04/16/2018 09:56 AM, Stefan Agner wrote: >> >> 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? >> > >> > You had best ask Thierry; he's taken over Tegra maintenance upstream. >> > But that said, don't files in arch/arm go through Russell? >> >> I think the last patches applied to that file went through your tree. >> >> Thierry, Russel, any preferences? > > I don't mind picking this up into the Tegra tree. Might be a good idea > to move this into drivers/firmware, though, since that's where all the > other firmware-related drivers reside. > > Firmware code, such as the BPMP driver, usually goes through ARM-SoC > these days. I think this is in the same category. > > Russell, any objections to me picking this patch up and moving it into > drivers/firmware? Please take this -- without it I'm seeing build failures on the arm allmodconfig under gcc 7.3.0: /tmp/ccKdsC59.s: Assembler messages: /tmp/ccKdsC59.s:35: Error: .err encountered /tmp/ccKdsC59.s:36: Error: .err encountered /tmp/ccKdsC59.s:37: Error: .err encountered scripts/Makefile.build:317: recipe for target 'arch/arm/firmware/trusted_foundations.o' failed The above patch fixes it for me. Thanks! -Kees -- Kees Cook Pixel Security From mboxrd@z Thu Jan 1 00:00:00 1970 From: keescook@chromium.org (Kees Cook) Date: Thu, 12 Jul 2018 15:43:10 -0700 Subject: [PATCH v2 3/6] ARM: trusted_foundations: do not use naked function In-Reply-To: <20180417081109.GA5804@ulmo> 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> <498de826-6e6c-63d8-00d6-f394b2725a34@wwwdotorg.org> <507a66ab9ab530a6d71db7a74f11ddfb@agner.ch> <20180417081109.GA5804@ulmo> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Apr 17, 2018 at 1:11 AM, Thierry Reding wrote: > On Mon, Apr 16, 2018 at 08:21:09PM +0200, Stefan Agner wrote: >> On 16.04.2018 18:08, Stephen Warren wrote: >> > On 04/16/2018 09:56 AM, Stefan Agner wrote: >> >> 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? >> > >> > You had best ask Thierry; he's taken over Tegra maintenance upstream. >> > But that said, don't files in arch/arm go through Russell? >> >> I think the last patches applied to that file went through your tree. >> >> Thierry, Russel, any preferences? > > I don't mind picking this up into the Tegra tree. Might be a good idea > to move this into drivers/firmware, though, since that's where all the > other firmware-related drivers reside. > > Firmware code, such as the BPMP driver, usually goes through ARM-SoC > these days. I think this is in the same category. > > Russell, any objections to me picking this patch up and moving it into > drivers/firmware? Please take this -- without it I'm seeing build failures on the arm allmodconfig under gcc 7.3.0: /tmp/ccKdsC59.s: Assembler messages: /tmp/ccKdsC59.s:35: Error: .err encountered /tmp/ccKdsC59.s:36: Error: .err encountered /tmp/ccKdsC59.s:37: Error: .err encountered scripts/Makefile.build:317: recipe for target 'arch/arm/firmware/trusted_foundations.o' failed The above patch fixes it for me. Thanks! -Kees -- Kees Cook Pixel Security