TF-M April 2020

tf-m@lists.trustedfirmware.org

25 participants
56 discussions

Re: [TF-M] Multi-threaded single-scheduler model proposal

by DeMars, Alan

Is pre-emption while in secure mode supported? If so, NS RTOS may have to be modified to handle switching from a thread who's PC and SP are in secure domain. How would a secure service thread block while waiting for a security-protected hardware process to finish (ie what is the secure driver model)? Alan From: TF-M [mailto:tf-m-bounces@lists.trustedfirmware.org] On Behalf Of Reinhard Keil via TF-M Sent: Thursday, April 2, 2020 5:49 AM To: tf-m(a)lists.trustedfirmware.org Cc: nd Subject: [EXTERNAL] [TF-M] Multi-threaded single-scheduler model proposal Hi Erik, Really great to see your involvement. Let me share my view on a TF-M execution model for constrained single core v8-M with TrustZone using Secure Function Call (aka library) mode: On secure side: single thread execution only. Not stack swapping. NS to S calls are blocking until secure execution completes. On non-secure side: RTOS with threaded execution. Entry to secure side protected with Mutex. This structure is explain on page 27 of https://github.com/ARM-software/CMSIS_5/blob/develop/CMSIS_Review_Meeting_2… IMHO, there are various benefits: * Overall less complexity, no need of tz_context, any RTOS would work, less memory overhead (i.e. single stack at secure side) * No impact to time deterministic execution on the NS side unless two threads call secure services * Conflict of mulitple threads calling secure services could be minimized with RTOS that offers priority inversion Are there any obvious problems with the above model? Thanks Reinhard Keil - Sr. Director Embedded Tools, Arm P.S. maybe you read also https://lists.trustedfirmware.org/pipermail/tf-m/2020-March/000805.html IMHO we need to simplify the NS to S call entry to speed-up the overall system

4 years

Re: [TF-M] Multi-threaded single-scheduler model proposal

by Ken Liu

Hi, Looks like another non-secure thread with higher priority could not access secure service since the secure context belongs to previous ongoing non-secure thread and tz_context is not proposed? /Ken From: TF-M <tf-m-bounces(a)lists.trustedfirmware.org> On Behalf Of Reinhard Keil via TF-M Sent: Thursday, April 2, 2020 9:52 PM To: DeMars, Alan <ademars(a)ti.com>; tf-m(a)lists.trustedfirmware.org Cc: nd <nd(a)arm.com> Subject: Re: [TF-M] Multi-threaded single-scheduler model proposal Alan, "I was afraid that this was the proposal. No lower priority NS threads can run while waiting for the secure interrupt. Only higher priority threads that are initiated by a NS interrupt can run." You are correct, scheduling of lower priority NS threads would be not possible. This is definitely a shortcoming of the solution. May I ask: how long does a hardware crypto operation take? What time could be used for low priority NS thread execution? Reinhard

4 years

Multi-threaded single-scheduler model proposal

by Reinhard Keil

Hi Erik, Really great to see your involvement. Let me share my view on a TF-M execution model for constrained single core v8-M with TrustZone using Secure Function Call (aka library) mode: On secure side: single thread execution only. Not stack swapping. NS to S calls are blocking until secure execution completes. On non-secure side: RTOS with threaded execution. Entry to secure side protected with Mutex. This structure is explain on page 27 of https://github.com/ARM-software/CMSIS_5/blob/develop/CMSIS_Review_Meeting_2… IMHO, there are various benefits: * Overall less complexity, no need of tz_context, any RTOS would work, less memory overhead (i.e. single stack at secure side) * No impact to time deterministic execution on the NS side unless two threads call secure services * Conflict of mulitple threads calling secure services could be minimized with RTOS that offers priority inversion Are there any obvious problems with the above model? Thanks Reinhard Keil - Sr. Director Embedded Tools, Arm P.S. maybe you read also https://lists.trustedfirmware.org/pipermail/tf-m/2020-March/000805.html IMHO we need to simplify the NS to S call entry to speed-up the overall system

4 years

Re: [TF-M] [TF-TSC] Project Maintenance Proposal for tf.org Projects

by Sandrine Bailleux

Hi Joakim, On 4/1/20 10:08 AM, Joakim Bech via TSC wrote: > Hi Christian, Sandrine, all, > > On Thu, Mar 26, 2020 at 10:27:14AM +0100, Sandrine Bailleux wrote: >> Hi Christian, >> >> Thanks a lot for the read and the comments! >> >> On 3/25/20 7:05 PM, Christian Daudt wrote: >>> ï¿½The maintenance proposal looks great ! I have some feedback on >>> specific portions: >>> ï¿½1. maintainer/owner/author patches. " Note that roles can be >>> cumulative, in particular the same individual can be both a code owner >>> and a maintainer. In such a scenario, the individual would be able to >>> self-merge a patch solely affecting his module, having the authority to >>> approve it from both a code owner and maintainer's point of view.": I'm >>> always leery of people self-approving their patches. At a minimum, all >>> self-patches should be published and a minimum wait time provided for >>> feedback. Or preferably that another maintainer does the merge (it does >>> not need to be mandated but should be suggested). >> >> Yes, actually this is something that generated some disagreement inside Arm >> as well and I am glad you're bringing this up here, as I'd like to hear more >> opinions on this. >> >> I too have concerns about allowing self-reviewing. I am not so much >> concerned about people potentially abusing of this situation to silently >> merge patches, as I think we should trust our maintainers. But I am worried >> that a self-review is rarely as good as a peer review, simply because it is >> so easy to miss things when it's your own work. I believe several pair of >> eyes is always better, as different people think differently, have different >> perspectives and backgrounds, and are able to catch different issues. >> >> But to pull this off, we need enough people to do all these reviews. The >> proposal currently allows self-review because some of us feared that >> mandating 2 reviewers for every patch (especially pure platform patches) >> would be impractical and too heavyweight, especially for the TF-M project in >> its current contributors organization, as I understand. It would be great to >> get more feedback from the TF-M community as to whether they think it could >> work in the end. >> >> It's a difficult balance between having the best possible code review >> practices, and realistically getting all the review work done in a timely >> manner, avoiding bottlenecks on specific people and keeping the flow of >> patches smooth. >> >> I like your idea of a minimum wait time provided for feedback. I think it >> could be a good middle ground solution. >> > +1 for that, after silence for X weeks it should be OK to merge the > patch. X would need to be number that is high enough for people to have > a chance to find it and look into it, but shouldn't be too high, since > there is a risk that it'll force the contributor to pile up things that > might be dependent on this patch. To throw something out, I'd say ~2 > weeks sounds like a good number to me. > >> Your other suggestion of having a different maintainer doing the merge would >> work as well IMO but requires more workforce. Again this comes down to >> whether this can realistically be achieved for each project. This solution >> was actually suggested within Arm as well (and even called out at the end of >> the proposal ;) ). >> >> Bottom line is, in an ideal world I would like to condemn self-review >> because I consider this as bad practice > +1 > >> , but I do not know whether this will >> be practical and will work for TF-M as well. >> >>> ï¿½2. 'timely manner': This expectation should be more explicit - when >>> the author can start requesting other maintainers to merge on assumption >>> that silence == approval (or not). Such timeliness expectations are >>> probably best set per project however. >> >> Yes, "timely manner" is definitely too vague and was actually left that way >> on purpose at this stage to avoid touching upon what I think is a sensitive >> subject! I am aware that some patches sometimes spend a long time in review, >> definitely longer than they should and it understandably generates some >> frustration. This is something we absolutely need to improve on IMO and >> hopefully a bigger pool of maintainers will help solve this issue. But I >> agree that the expected review timeline should be clearly established and it >> is probably best to let each project decides theirs. >> >>> ï¿½3. The proposal does not address branching strategies. i.e. will >>> there be separate maintainers for dev/master/stable branches? I don't >>> think it needs to address it yet - keep it simpler for a start. But a >>> todo saying something like "in the future this project maintenance >>> proposal might be expanded to address multi-branch maintainership" would >>> be good. >> >> Good point. A todo sounds good, I will add one in the last section of the >> document. >> >>> ï¿½4. The platform lifecycle state machine has too many transitions. >>> "Fully maintained" <-> "orphan" -> "out" seems sufficient to me. >> >> Hmm OK. There might be too many transitions but I feel we need something >> between fully maintained and out, i.e. the limited support one. >> >> Julius Werner also pointed out on Thursday that orphan might be misplaced, >> as all these other stages deal with some degrees of feature support (what's >> known to work), whereas orphan is an orthogonal topic that is not directly >> related to the level of supported features. For example, a platform could >> have recently become orphan but all features and tests still work for some >> time. >> > At one point in time in the OP-TEE project we tried to keep track of > maintained platforms, by simply saying maintained "Yes" if they are > maintained. However they're not maintained, we indicated that by stating > the last known version where a platform was maintained. People can still > find that information here [1] (not up-to-date). The intention was to > give future users of an old platform a chance to know if it ever has > been supported and what version that was. That could serve as a starting > point in case someone is interested in bring a device/platform back to > life. Yes, I think such information can be very useful. It saves some "git archeology" effort to try and dig this information afterwards. Also, when someone starts looking at a project, I would expect this to be one of the first thing they look up, they would want to know in which shape the project is for the particular platform they are interested in. That's almost as important in my eyes as a "getting started" guide. We could have such a high-level table that just says whether a platform is supported or not (just a yes/no) and have complementary, per-platform documentation that goes into the details of what features are supported exactly. > How that works in practice is that all OP-TEE maintainers are adding > their "Tested-by" (see example [2]) tag for the platform they maintain > when we're doing a release. If there are platforms with no "Tested-by" > tag, then they simply end up with the "last known version". I think that's a very good idea! > However, to keep that up-to-date, it requires some discipline from the > people maintaining such a table ... something that we in the OP-TEE > project haven't been very good at :) Can't this be automated, such that it doesn't need to be manually kept up-to-date? I imagine we could have some tools generating the platform support table out of such a commit message. > So, I'm not proposing something, it's just that I wanted to share what > we've tried and it "works", but not easy to maintain (a release > checklist could fix that). > > [1] https://optee.readthedocs.io/en/latest/general/platforms.html > [2] https://github.com/OP-TEE/optee_os/pull/3309/commits/765b92604459240bed7fcf… >

4 years

Re: [TF-M] [EXTERNAL] Project Maintenance Proposal for tf.org Projects

by Shreve, Erik

Sandrine, Really glad to see this being pulled together. A couple of areas of feedback around the Platform Support Life Cycle. As previously mentioned there are two orthogonal concerns captured in the current life cycle: Support and Functionality. I'd like to see these split out. For functionality, chip vendors may not have a business case for supporting all features on a given platform but they may provide full support for the features they have chosen to include. A simple example would be supporting PSA FF Isolation Level 1 only due to lack of HW isolation support needed to achieve Isolation Level 2 or greater. Also, I'd like to see a stronger standard put forth for platform documentation. If a platform is "supported," I believe the documentation should be complete and accurate. A lack of complete and clear documentation leaves open a wide door for misuse/misconfiguration which could result in a vulnerable system. Here is a more concrete proposal: Functional Support: Each project shall provide a standard feature or functionality list. Each platform shall include in its documentation a copy of this list with the supported functionality marked as supported. The platform documentation may reference a ticket if support is planned but not yet present. The platform documentation shall explicitly state if a feature or function has no plans for support. The feature/functionality list shall be versioned, with the version tied to the release version(s) of the project. In this way, it will be clear if a platform was last officially updated for version X but the project is currently at version Y > X. Note: projects will need to adopt (if they have not already) a version scheme that distinguishes between feature updates and bug fixes. Each project and platform shall use tags or similar functionality on tickets to associate tickets to features/functionality and platforms. If the names of tags can't match the name of the feature or platform exactly then a mapping shall be provided in the appropriate document(s). Life Cycle State Fully Supported There is (at least) one active code owner for this platform. All supported features build and either all tests pass or failures are associated with tracked known issues. Other (not associated to a test) Known Issues are tracked Documentation is up to date Note: Projects should document standards on how "active" code ownership is measured and further document standards on how code owners are warned about impending life cycle state changes. Orphan There is no active code owner All supported features build and either all tests pass or failures are associated with tracked known issues. Other (not associated to a test) Known Issues may not have been maintained (as there is no active code owner) Documentation status is unclear since there is no active code owner. There has been no change to the feature/functionality list in the project since the platform was last "Fully Supported" Out of date Same as orphan, but either: there have been changes to the feature/functionality list, or there are failing tests without tracked tickets, or there are known documentation issues. Deprecated Same as Out of Date, but the build is broken. Platform may be removed from the project codebase in the future. Erik Shreve, PSEM Software Security Engineer & Architect (CMCU Platform Development) -----Original Message----- From: TF-M [mailto:tf-m-bounces@lists.trustedfirmware.org] On Behalf Of Sandrine Bailleux via TF-M Sent: Tuesday, March 24, 2020 4:42 AM To: tf-a; tf-m(a)lists.trustedfirmware.org; tsc(a)lists.trustedfirmware.org; op-tee(a)linaro.org Cc: nd(a)arm.com Subject: [EXTERNAL] [TF-M] Project Maintenance Proposal for tf.org Projects Hello all, As the developers community at trustedfirmware.org is growing, there is an increasing need to have work processes that are clearly documented, feel smooth and scale well. We think that there is an opportunity to improve the way the trustedfirmware.org projects are managed today. That's why we are sharing a project maintenance proposal, focusing on the TF-A and TF-M projects initially. The aim of this document is to propose a set of rules, guidelines and processes to try and improve the way we work together as a community today. Note that this is an early draft at this stage. This is put up for further discussion within the trustedfirmware.org community. Nothing is set in stone yet and it is expected to go under change as feedback from the community is incorporated. Please find the initial proposal here: https://developer.trustedfirmware.org/w/collaboration/project-maintenance-p… Please provide any feedback you may have by replying to this email thread, keeping all 4 mailing lists in the recipients list. I will collate comments from the community and try to incorporate them in the document, keeping you updated on changes made between revisions. Regards, Sandrine -- TF-M mailing list TF-M(a)lists.trustedfirmware.org https://lists.trustedfirmware.org/mailman/listinfo/tf-m

4 years

Re: [TF-M] Project Maintenance Proposal for tf.org Projects

by Christian Daudt

Hi Sandrine, > Please find the initial proposal here: > > https://developer.trustedfirmware.org/w/collaboration/project-maintenance-p… > > Please provide any feedback you may have by replying to this email > thread, keeping all 4 mailing lists in the recipients list. > > I will collate comments from the community and try to incorporate them > in the document, keeping you updated on changes made between revisions. The maintenance proposal looks great ! I have some feedback on specific portions: 1. maintainer/owner/author patches. " Note that roles can be cumulative, in particular the same individual can be both a code owner and a maintainer. In such a scenario, the individual would be able to self-merge a patch solely affecting his module, having the authority to approve it from both a code owner and maintainer's point of view.": I'm always leery of people self-approving their patches. At a minimum, all self-patches should be published and a minimum wait time provided for feedback. Or preferably that another maintainer does the merge (it does not need to be mandated but should be suggested). 2. 'timely manner': This expectation should be more explicit - when the author can start requesting other maintainers to merge on assumption that silence == approval (or not). Such timeliness expectations are probably best set per project however. 3. The proposal does not address branching strategies. i.e. will there be separate maintainers for dev/master/stable branches? I don't think it needs to address it yet - keep it simpler for a start. But a todo saying something like "in the future this project maintenance proposal might be expanded to address multi-branch maintainership" would be good. 4. The platform lifecycle state machine has too many transitions. "Fully maintained" <-> "orphan" -> "out" seems sufficient to me. Thanks, Christian. This message and any attachments may contain confidential information from Cypress or its subsidiaries. If it has been received in error, please advise the sender and immediately delete this message.

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TF-M April 2020