May 2022 - TF-M - lists.trustedfirmware.org

Re: [TF-M] Supporting encryption with ITS

by Sherry Zhang

Hi George, The ITS without encryption is not a compromised RoT. In the PSA Secure Storage API spec, the PSA Internal Trust Storage aims at providing a place for devices to store their most intimate secrets. Also “””””””””””””””””””” 1. The storage underlying the PSA Internal Trusted Storage Service MUST be protected from read and modification by attackers with physical access to the device. 2. The storage underlying the PSA Internal Trusted Storage Service MUST be protected from direct read or write access from software partitions outside of the PSA Root of Trust (PRoT). “””””””””””””””””””” So, for internal trusted storage service, it requires the underlying storage itself should provide being read or write protection. The storage area should be a “trusted” area. Does the storage area on your device meet this requirement? Is the memory physically isolated? If not, I wonder why not uses the Protected Storage service instead? For the design of adding encryption in ITS, in the PS partition, the `iv` and the encrypted object data are stored with the object file while the tag of each object is stored with the object table file. So, if encrypt the PS object in the ITS file system, how the PS partition get the `tag` of each object? After a rough thought, I think probably a standalone encryption for ITS is more reasonable. As this is a relatively “big topic”, would you like to hold a discussion on the TF-M Tech forum if it is not limited by confidential information? The next Tech forum will be hold on this Thursday 3:00 PM UTC time. Regards, Sherry Zhang From: Vasilakis, Georgios <georgios.vasilakis(a)nordicsemi.no<mailto:georgios.vasilakis@nordicsemi.no>> Sent: Friday, September 24, 2021 8:52 PM To: Sherry Zhang <Sherry.Zhang2(a)arm.com<mailto:Sherry.Zhang2@arm.com>>; tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org> Cc: nd <nd(a)arm.com<mailto:nd@arm.com>> Subject: Re: [TF-M] Supporting encryption with ITS Hello Sherry, Thank you for your input! 1. Our threat model is more concerned about attacks which can happen very early in the boot process, I think. A completely compromised RoT is not in our threat model. 2. I see that, ITS is supposed to store small objects. The storage overhead of adding encryption will be probably bigger than 20 bytes I think but the intention is to have this only as a configuration, not as the default option. 3. Agreed, a HAL API should be used for this. Do you have any opinion on the design of it? Do you think that it adds value to do try to use a common design for the object handling of both PS and ITS or is it better to have it as a standalone thing for the ITS. Regards, George ________________________________ From: Sherry Zhang <Sherry.Zhang2(a)arm.com<mailto:Sherry.Zhang2@arm.com>> Sent: Friday, September 24, 2021 11:58 AM To: Vasilakis, Georgios <georgios.vasilakis(a)nordicsemi.no<mailto:georgios.vasilakis@nordicsemi.no>>; tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org> <tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org>> Cc: nd <nd(a)arm.com<mailto:nd@arm.com>> Subject: RE: [TF-M] Supporting encryption with ITS Hi George, Some comments from my side: 1. Internal trusted storage is part of the Root of Trust domain. If ITS storage device is attacked, then the code flash where the PSA Rot SP locates may also be attacked. Does the thread model of your system require the encryption in ITS? 2. The ITS service is intended to be used to interface to a small piece of storage. Encryption would increase the context for each ITS file. For example, similarly to PS object context, the `IV` which is used in encryption as well as the generated `tag` should be added into each file context. They total together can be about more than 20 bytes. 3. If the encryption is mandatory/ necessary required by the thread model of your system, as discussed, the PSA crypto service should not be called to avoid the circular. I think a HAL API for encryption may be created in ITS for platform implementation defined encryption/decryption. Regards, Sherry Zhang From: TF-M <tf-m-bounces(a)lists.trustedfirmware.org<mailto:tf-m-bounces@lists.trustedfirmware.org>> On Behalf Of Vasilakis, Georgios via TF-M Sent: Thursday, September 23, 2021 10:47 PM To: Gyorgy Szing <Gyorgy.Szing(a)arm.com<mailto:Gyorgy.Szing@arm.com>>; Fabian Schmidt <fabian.schmidt(a)nxp.com<mailto:fabian.schmidt@nxp.com>> Cc: nd <nd(a)arm.com<mailto:nd@arm.com>>; tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org> Subject: Re: [TF-M] Supporting encryption with ITS Hey Gyorgy, These are very valuable comments! I am aware of the circular dependency issue because the PSA apis are using the ITS as a storage backend. This, as you said, can be circumvented by using a software crypto library or an implementation specific API. So, for the encryption a flexible API can be used which can allow externals to use their own function calls. Regarding the key storage, this is what I had in mind as well, using derived keys from the HUK. So that we don't need to store anything but the crypto metadata. Adding another layer of storage will raise more issues, I think. ________________________________ From: Gyorgy Szing <Gyorgy.Szing(a)arm.com<mailto:Gyorgy.Szing@arm.com>> Sent: Thursday, September 23, 2021 4:30 PM To: Fabian Schmidt <fabian.schmidt(a)nxp.com<mailto:fabian.schmidt@nxp.com>>; Vasilakis, Georgios <georgios.vasilakis(a)nordicsemi.no<mailto:georgios.vasilakis@nordicsemi.no>> Cc: tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org> <tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org>>; nd <nd(a)arm.com<mailto:nd@arm.com>> Subject: RE: [TF-M] Supporting encryption with ITS Hi, AFAIK the main reason for ITS not using encryption is the problem of circular dependency. ITS is used by crypto SP for key storage, so how will crypto fetch the key from ITS to decrypt ITS? You could use a software crypto implementation (another mbed-tls instance) in ITS, but where would you safely store the keys? If you have a two layer ITS, one for only storing the keys for the second instance, and a second, encrypted one, then you end up with something like ITS and PS. You may not need a full blown on-chip FLASH device for ITS. If you have a HUK available, you can derive the same SP specific keys from that at each boot, and store these in RAM backed ITS. You won’t be able to store other keys in ITS in a persistent way of course, but for that you can use PS. Well, something along these lines. Perhaps the TF-M team could help better if you could share some details on why your customer would need encrypted ITS. (A PSA for Cortex-A (TS) maintainer chiming in to a “not his business” discussion here 😉 ) /George From: TF-M <tf-m-bounces(a)lists.trustedfirmware.org<mailto:tf-m-bounces@lists.trustedfirmware.org>> On Behalf Of Fabian Schmidt via TF-M Sent: September 23, 2021 15:51 To: Vasilakis, Georgios <georgios.vasilakis(a)nordicsemi.no<mailto:georgios.vasilakis@nordicsemi.no>> Cc: tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org> Subject: Re: [TF-M] Supporting encryption with ITS Hi George, I’m wondering if that would add value. To my understanding, ITS was never designed to be encrypted because of the way it’s supposed to be set up. (It’s Internal Trusted Storage.) I believe best practice is to place it in a “trusted” location, one that is ideally only accessible from Secure world, and also ideally on-die. If you then restrict outside access to the internal flash (JTAG, flash programmer ports,…), you’re pretty golden, in that no unauthorized party should be able to read from or write to the ITS.* Let me know if I misunderstand anything about ITS or TrustZone, but that’s my view. Maybe I’m painting an idealized picture. Greetings, Fabian Schmidt * at least short of a sophisticated physical attack or finding some loophole in TrustZone… From: TF-M <tf-m-bounces(a)lists.trustedfirmware.org<mailto:tf-m-bounces@lists.trustedfirmware.org>> On Behalf Of Vasilakis, Georgios via TF-M Sent: Donnerstag, 23. September 2021 15:28 To: tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org> Subject: [EXT] [TF-M] Supporting encryption with ITS Caution: EXT Email Hey all, Lately the requirement for an encrypted ITS solution is being asked from our customers and I would like to have a discussion here on how we can design this in a reasonable way. The first thought that came to my mind was to add the functionality to the ITS flash-fs layer. This layer contains file metadata in the its_file_meta_t structure and it should be possible to expand this to include additional crypto metadata (conditionally). This seems to be the less invasive change to me, even though it will introduce some increased memory usage since supporting encryption will mean that we cannot read the data in chunks anymore, we will have to use static buffers. At the same time, I looked at the PS partition since I knew that it has support for encryption. I believe that some core concepts of both solutions have similarities even though the code is quite different. For example, a file in ITS is similar to an object in PS and the (linear) list of file metadata in ITS is similar to the concept of the object table in PS. So, I think that it should be possible to design some generic-enough APIs that we can use for both the ITS and PS. Even though this will require some major refactoring in both partitions, it will decrease the code of these services which will probably decrease maintenance later. What are your thoughts on this? Regards, George

6 months, 1 week

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Documentation improvements

by Anton Komlev

Hello, The project documentation will never be ideal and we are continuing improving it. Let me ask you for reply to this email with the pain points you have experienced or suggestions for improvements to be considered in this phase. Your direct contribution with docs articles will be much appreciated too. For example: TF-M debugging technics and experience would be very helpful. Thank you in advance, Anton

7 months, 3 weeks

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Re: Attestation token new spec

by Tamas Ban

Hi, Sorry 2nd link was broken. Here is the working version: https://www.ietf.org/archive/id/draft-tschofenig-rats-psa-token-09.html#tab… Tamas Ban From: Andersson, Joakim <Joakim.Andersson(a)nordicsemi.no> Sent: 2022. május 9., hétfő 12:14 To: Tamas Ban <Tamas.Ban(a)arm.com> Subject: RE: Attestation token new spec Is te second link broken? I get a 404 error code. -Joakim From: Tamas Ban via TF-M <tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org>> Sent: mandag 9. mai 2022 11:31 To: tf-m(a)lists.trustedfirmware.org<mailto:tf-m@lists.trustedfirmware.org> Cc: nd <nd(a)arm.com<mailto:nd@arm.com>> Subject: [TF-M] Attestation token new spec Hi, the initial attestation token implementation is aligned with this specification: https://datatracker.ietf.org/doc/html/draft-tschofenig-rats-psa-token-05<https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdatatrack…> This spec is still evolving and there is a newer version which changes the key values of the claims in the token: https://www.ietf.org/archive/id/draft-tschofenig-rats-psa-token-09.html#tab…<https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ietf.…> This can cause combability issues between token issuer (device) and token verifier (some remote verification service). This is an ABI change between token issuer and consumer. The breaking effect would be manifest in unaccepted IAT tokens by the verifier. On-device side I see these options to make the transition: - A build-time option could be introduced which determines which range of key numbers to use. The default value would be the new range. To not let new users pick up the old values accidentally. Existing users can notice the incompatibility issue during the integration test and adjust their build command accordingly. However, the old range would be announced as deprecated in the next TF-M release, then will be removed in the next release after. - Immediate switch over to the new range, without supporting the old range anymore. On the verification service side, an SW update can handle the transition and might be accepting both ranges for a while. I assume the verification service can be updated more easily than remote devices therefore better to handle the compatibility issue there. - Keeping the support for both ranges for the long term and letting users choose by build time. Please share your thoughts on: - Are you aware that the attestation service is used in deployed devices where this transition can cause incompatibility? - From the above list which option would you vote to support the transition? Best regards, Tamas Ban

8 months, 1 week

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Library fetching improvements

by Bohdan.Hunko＠infineon.com

Hi, Recently I have been adding some new libraries to my TFM project and what I always end up doing is: go to some existing file which fetches the library, copy code from there, paste it to my file, change few links, versions and names. It is a bit annoying to copy-paste that code each time, also it is hard to maintain (if pattern for fetching libraries changes) and also copy pasting might lead to some code not being updated. My proposal is to have a function that can be used to fetch a library. This way it will be easier to add new libraries and this change will make code cleaner. Please let me know your thoughts on this proposal. Regards Bohdan Hunko Cypress Semiconductor Ukraine Engineer CSUKR CSS ICW SW FW Mobile: +38099 50 19 714 Bohdan.Hunko(a)infineon.com<mailto:Bohdan.Hunko@infineon.com>

8 months, 3 weeks

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Automatically copy RAM_VECTORS when using ARMClang and IAR

by Bohdan.Hunko＠infineon.com

Hi, When poking around some startup files I have found interesting place related to RAM_VECTORS support CMSIS have __PROGRAM_START macro which is different for each compiler. For GCC it uses __cmsis_start, for ARMClang - __main and for IAR - __iar_program_start Basically each of the functions should copy several sections (.TFM_DATA for example) from FLASH to RAM and zero out some parts of RAM (for .TFM_BSS for example) In current implementation GCC __cmsis_start function also copies the vector table from FLASH to SRAM (if RAM_VECTORS are enabled) But ARMClang and IAR equivalents of that function (__main, __iar_program_start) does not seem to take care of copying vector table, so platforms startup should do that I wonder if there is a way to change linker script in a way which will make copying of vector table automatic (by compiler dependent function). This will make platform startups a bit cleaner and will allow platform to just use __PROGRAM_START macro without any additional code to copy vector table. From what I see IAR has "initialize by copy" syntaxis so I think it may be used to tell IAR to automatically copy vector table. It is a bit more tricky with ARMClang as I have not found a way to do that there. I am not a big expert in ARMClang and IAR so maybe someone may help me here, give some directions or confirm that currently there is no way to make this idea work. Basically the intention is to simplify platform startup code and offload common operations to compiler specific platform independent functions. Regards, Bohdan Hunko Cypress Semiconductor Ukraine Engineer CSUKR CSS ICW SW FW Mobile: +38099 50 19 714 Bohdan.Hunko(a)infineon.com<mailto:Bohdan.Hunko@infineon.com>

8 months, 3 weeks

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Usage of TFM_SYSTEM_FP cmake variable

by Bohdan.Hunko＠infineon.com

Hi everyone, I have noticed that GCC toolchain uses CONFIG_TFM_FP to determine FP setting while IAR and Clang use TFM_SYSTEM_FP cmake variable. I was not able to find any docs on this variable, and also there is no assignment of this variable in TFM source code (only read operation from this variable). Is this intendent behavior? Regards, Bohdan Hunko Cypress Semiconductor Ukraine Engineer CSUKR CSS ICW SW FW Mobile: +38099 50 19 714 Bohdan.Hunko(a)infineon.com<mailto:Bohdan.Hunko@infineon.com>

9 months, 2 weeks

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Technical Forum call - May 26

by Anton Komlev

Hi, The next Technical Forum is planned on Thursday, May 26, 7:00-8:00 UTC (East time zone). Please reply on this email with your proposals for agenda topics. Recording and slides of previous meetings are here: https://www.trustedfirmware.org/meetings/tf-m-technical-forum/ Best regards, Anton

10 months

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tfm_arch_is_priv() is not available for v8arch

by Bohdan.Hunko＠infineon.com

Hi everyone, While looking through TFM code I have noticed that tfm_arch_is_priv() is defined for v6 and v7 in secure_fw/spm/cmsis_psa/arch/tfm_arch_v6m_v7m.h but not defined for v8. Also tfm_arch_v6m_v7m.h is located in secure_fw/spm/cmsis_psa/arch/ folder, while tfm_arch_v8m.h is located in secure_fw/spm/include/. I think that tfm_arch_is_priv() should also be defined for v8 and also tfm_arch_v6m_v7m.h should be moved to secure_fw/spm/include/. If file will be moved then we can clean up some target_include_directories() which used secure_fw/spm/cmsis_psa/arch/ folder. Any thoughts on this? Regards, Bohdan Hunko Cypress Semiconductor Ukraine Engineer CSUKR CSS ICW SW FW Mobile: +38099 50 19 714 Bohdan.Hunko(a)infineon.com<mailto:Bohdan.Hunko@infineon.com>

10 months

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Split build

by Bohdan.Hunko＠infineon.com

Hi everyone, Some time ago patch for split build<https://review.trustedfirmware.org/q/topic:%2522split-build%2522> of SPE, NSPE, BL2 was announced. I am interested on when this patch is planned to be merged? Regards, Bohdan Hunko Cypress Semiconductor Ukraine Engineer CSUKR CSS ICW SW FW Mobile: +38099 50 19 714 Bohdan.Hunko(a)infineon.com<mailto:Bohdan.Hunko@infineon.com>

10 months

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Re: Enable SPI interrupt in secure partition

by Edward Yang

Hi Kevin, Thanks for your instruction. We're developing an application RoT partition which access a sensor via an SPI interface(Based on RA6M4_EK development board). After commands have been transferred to the sensor, an SPI_TX_INTERRUPT should be triggered, then calls spi_tx_isr(). Now let's put aside binding secure interrupts to each secure partition, just talk about how to enable SPI interrupts in secure world simply. Here is my implementation: 1.Configure this SPI peripheral as secure peripheral. 2.Assign SPI tx and rx interrupts to secure state by setting NVIC->ITNS register. 3.Enable SPI tx and rx interrupts by seeting NVIC->ISER register. But during debug, I found that spi0_tx_isr() (The ISRs are also placed under this application RoT partition's folder) has never been triggered. Is there anything that I miss? Best Regards, Poppy Wu 吴偏偏 Macronix Microelectronics (Suzhou) Co.,Ltd 旺宏微电子（苏州）有限公司 http://www.mxic.com.cn Kevin Peng via TF-M <tf-m(a)lists.trustedfirmware.org> 2022/05/17 09:45 Please respond to Kevin Peng <Kevin.Peng(a)arm.com> To Edward Yang <EdwardYang(a)mxic.com.cn>, "tf-m(a)lists.trustedfirmware.org" <tf-m(a)lists.trustedfirmware.org> cc Subject [TF-M] Re: Enable SPI interrupt in secure partition Hi Poppy, First-Level Interrupt Handling (FLIH) should be recommended in your use case as you have latency requirements. Here is an example: https://git.trustedfirmware.org/TF-M/tf-m-tests.git/tree/test/secure_fw/sui… You’ll firstly need to add an “irq” item in the manifest and “handling ” it with “FLIH”: https://git.trustedfirmware.org/TF-M/tf-m-tests.git/tree/test/secure_fw/sui… And also add the “mmio_regions” item with the associated device (SPI) to give access permissions to the Secure Partition. The IRQ handling should be in the Secure Partition: https://git.trustedfirmware.org/TF-M/tf-m-tests.git/tree/test/secure_fw/sui… Note that, no PSA APIs are allowed in the handling. Best Regards, Kevin From: Edward Yang via TF-M <tf-m(a)lists.trustedfirmware.org> Sent: Monday, May 16, 2022 5:38 PM To: tf-m(a)lists.trustedfirmware.org Subject: [TF-M] Enable SPI interrupt in secure partition Hi experts, Recently we're developing a demo based on TF-M, this demo involves using SPI module to drive a sensor by sending commands in a secure partition. And we need to enable SPI receive and send interrupt in this secure partition and the latency shall be as small as possible. I am wondering how to implement this secure interrupts. Is there any example code or instrucstions? Thanks. Best Regards, Poppy Wu 吴偏偏 Macronix Microelectronics (Suzhou) Co.,Ltd 旺宏微电子（苏州）有限公司 http://www.mxic.com.cn CONFIDENTIALITY NOTE: This e-mail and any attachments may contain confidential information and/or personal data, which is protected by applicable laws. Please be reminded that duplication, disclosure, distribution, or use of this e-mail (and/or its attachments) or any part thereof is prohibited. If you receive this e-mail in error, please notify us immediately and delete this mail as well as its attachment(s) from your system. In addition, please be informed that collection, processing, and/or use of personal data is prohibited unless expressly permitted by personal data protection laws. Thank you for your attention and cooperation. Macronix International Co., Ltd. =====================================================================-- TF-M mailing list -- tf-m(a)lists.trustedfirmware.org To unsubscribe send an email to tf-m-leave(a)lists.trustedfirmware.org ============================================================================ CONFIDENTIALITY NOTE: This e-mail and any attachments may contain confidential information and/or personal data, which is protected by applicable laws. Please be reminded that duplication, disclosure, distribution, or use of this e-mail (and/or its attachments) or any part thereof is prohibited. If you receive this e-mail in error, please notify us immediately and delete this mail as well as it attachments from your system. In addition, please be informed that collection, processing, and/or use of personal data is prohibited unless expressly permitted by personal data protection laws. Thank you for your attention and cooperation. Macronix International Co., Ltd. =====================================================================

10 months, 1 week

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