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TF-A Tech Forum @ Thu 9 Apr 2020 17:00 - 18:00 (GMT) - Special session on Project Maintenance Proposal for tf.org

by Joanna Farley

Hi All, The third TF-A Tech Forum is scheduled for Thu 9th Apr 2020 17:00 - 18:00 (GMT). A reoccurring meeting invite has been sent out to the subscribers of this TF-A mailing list. If you don’t have this please let me know. For this special session I have also copied the TF-M, TSC and OPTEE mailing lists as the subject may interest the people subscribed to those lists as there is a cross mailing list discussion currently ongoing. Agenda: * Overview of the Project Maintenance Proposal for tf.org Projects by Sandrine Bailleux * Optional TF-A Mailing List Topic Discussions Thanks Joanna IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

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

by Sandrine Bailleux

Hi Joakim, On 4/2/20 10:18 AM, Joakim Bech via TF-A wrote: > Hi Sandrine, > > On Wed, Apr 01, 2020 at 11:46:20AM +0200, Sandrine Bailleux wrote: >> Hi Joakim, >> >> On 4/1/20 10:08 AM, Joakim Bech via TSC wrote: >>> 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! >> > The "Tested-by" part for OP-TEE releases has been working pretty good, > not sure how scalable it is the long run though. To give some more > info regarding the "last known version", we even at one point had some > stop-light for that. I.e. if a maintainer missed testing a release once, > then it became "orange". If missed twice, then it became "red" and we > showed last know supported version. But we dropped that idea a short > while after introducing it. May I know why you dropped the idea? Was it too much maintenance? If that's the reason I guess again this could be addressed with some automation work (generating the stop-light status from the commit message info). >>> 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. >> > Indeed it could, it's just a matter of doing some scripting if one > doesn't want to do it manually. I already have Python scripts pulling > all tags from GitHub pull requests. But there are of course several > other ways how one could pull that kind of information. Regards, Sandrine

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

by Sandrine Bailleux

Hi Erik, On 4/1/20 9:24 PM, Shreve, Erik via TF-A wrote: > Sandrine, > > To clarify on functionality vs. support. I listed out a support life cycle consisting of the following states: > Fully Supported > Orphan > Out of Date > Deprecated > These states are intended to have nothing to do with functionality, but only the support offered for the functionality that currently exists for a platform. > > I think I may have confused things when I listed "Functional Support" as the heading to represent "Functionality." > I'm proposing that the supported "Functionality" should be documented in a standard way (within a project) for every platform. > > I do agree this could be burdensome to keep up with. But that is why I suggested that the project's feature list be versioned. The platform's supported feature list document would reference the version of the project feature list used. Platform maintainers then don' t have to continuously update the document. But it will be clear how long it has been since they did update and thus what information may be missing. Versioning the feature list document is also why I mentioned that the project version number may want to adopt a version number scheme where feature changes are represented by a certain part of the version number. For example Semantic Versioning 2.0.0: https://semver.org/. Hope that clarifies the intent? For implementation of this I'm imagining each project could create a supported_feature_list.rst file and each platform would copy that file into their platform doc folder and fill it in. I'm not saying that approach would be required at tf.org level, just sharing to further illustrate. > > That said, perhaps the implementation details for a project would not warrant such a document per platform? My primary concern around this is misuse/misconfiguration. If a platform doesn't support a feature or configuration it may not be obvious to a user unless an error is generated at build or run-time. OK, I think I get the idea now, thanks for the explanations. This looks reasonable to me. The idea of keeping a project's feature list being mirrored and filled in per platform sounds like something we would want to enforce at the tf.org level IMO. At the same time, this could also be handled at the build system level as you pointed out, or more precisely by the configuration manager. I am thinking about the Linux kernel, where support for a particular feature is handled (and documented) through the KConfig system. This might be a more scalable approach. And it doesn't prevent us from also auto-generating some feature list out of the Kconfig files for making this information more accessible to users. > My secondary concern is being able to consistently track tickets/bugs with features. Thus, I'm recommending that the features on that list be used with the ticket/issue system by feature name. This would allow users to find all bugs for Feature X on Platform Y in Project Z. > Related to that, when I mentioned "tags." I wasn't thinking of Git tags, but "labels" in the ticket/issue tracking system(s). Different systems work differently for labeling/categorizing issues, but the goal is to provide a consistent way (per project) to find issues related to a feature on a platform. > > If requiring a feature list it is too much at the tf.org level then I'll be satisfied to push for that kind of documentation in the projects or platforms I'm involved in if/as appropriate. Yes, good point, I think it would be desirable to be able to tie tickets to some specific platform/feature/version. And I think it makes sense to unify this across tf.org projects. > Regarding the other conversational tidbits: > > Thanks for pointing out that the original proposal does say "builds all configurations supported by this platform" under "Fully Supported." I can see the intention here now. Substituting "features" for "configurations" would broaden the meaning a bit. OK, I will change the wording, thanks for the suggestion. > You said: "I am starting to think that we need a list of items to be defined per project." > Yes, this sounds like a great idea. > > My original mention of wanting a "stronger standard put forth for platform documentation" was a response to seeing "Limited Support" in the original proposal allowing documentation to fall out of date. > > > Hope that clarifies some of my thoughts. If not, I'm happy to continue the discussion. Thanks again for taking feedback! > > Erik Shreve, PSEM > Software Security Engineer & Architect (CMCU Platform Development) > > -----Original Message----- > From: Sandrine Bailleux [mailto:sandrine.bailleux@arm.com] > Sent: Wednesday, April 01, 2020 4:18 AM > To: Shreve, Erik; tf-a; tf-m(a)lists.trustedfirmware.org; tsc(a)lists.trustedfirmware.org; op-tee(a)linaro.org > Cc: nd(a)arm.com > Subject: Re: [EXTERNAL] [TF-M] Project Maintenance Proposal for tf.org Projects > > Hello Erik, > > Thanks for the feedback. > > On 3/26/20 3:37 PM, Shreve, Erik wrote: >> 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. > > Yes, you are the second person to mention that and I agree with you > both. Unless someone disagrees, I intend to update the proposal and > separate these 2 concepts in the next version of the document. > >> 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. > > I completely agree. It would not make sense to support all features on > all platforms just for the sake of completeness. Each platform ought to > implement what is relevant in its case. > > That's what the current proposal tried to convey: a fully supported > platform must "build all configurations *supported by this platform*" > and "All *supported* configurations are tested in the CI". The key word > here is supported and that would be defined by the platform itself. But > I can see that maybe this wasn't clear enough. Your proposal below makes > that a lot clearer. > >> 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. > > Fair point. > > But is it something we should include in this proposal or should we push > it to a separate document setting expectations for the project's > documentation, which the current general proposal could refer to (as in, > "the platform should provide quality documentation up to the project's > criteria defined in document XXX')? > > This is definitely an important topic but I am wary of keeping the > tf.org proposal concise and focused at this point. I am worried that if > we put too much stuff in it discussions will diverge too much and we > might never reach an agreement. > > The same applies to testing standards for example, we could detail that > in the proposal or simply leave it to projects to define it separately. > >> 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. > > Regarding the last item, this would require all platform maintainers to > update their documentation every time a new feature is added to the > project's global list of features. This seems too much of a constraint > and unnecessary maintenance burden to me. > > I think a better, more lightweight alternative might be to let platform > maintainers list what's supported and if some feature is not listed, it > implies that it is not supported. This does not prevent platform > maintainers from indicating their future plans of supporting a feature > if they want to. > >> 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. > > I can see that Joakim Bech proposed something similar, with more details > about how this was implemented for OP-TEE. > >> Note: projects will need to adopt (if they have not already) a version scheme that distinguishes between feature updates and bug fixes. > > Sorry I didn't get this, could you please elaborate? > >> 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). > > If there's no appropriate tag in some cases, I guess we could always use > a git SHA1 of a specific commit. > >> 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. > > Yes, good point, that is currently undefined in the proposal but I agree > that it needs defining per project. I will add an item in the last > section of the document. > > I am starting to think that we need a list of items to be defined per > project. This list would complement the general tf.org proposal. Things > like code owners/maintainers activity, code review timelines, and so on. > >> >> 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" > > I am confused, you said earlier that you would like to see the concepts > of support and functionality split out, but here you're listing 'orphan' > as one of the possible states... Did I miss your point? > >> 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)

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Re: [TF-A] fconf: Validating config data

by Louis Mayencourt

Hi Raghu, I do agree with you: case 2 and 3 are similar (wrongly formed DTB) and should lead to the same behavior. A mandatory property miss or a hit with a structurally incorrect node means that the DTB doesn't follow the provided binding document. Such a DTB shouldn't be considered as valid and should trigger a build failure and/or a code panic. With the current implementation, case 2 and 3 are similar. The property_getter() functions expect a specific format of the node. If a node is not found or structurally incorrect, the function will return an error code, which will lead to a panic(). regards, Louis ________________________________ From: TF-A <tf-a-bounces(a)lists.trustedfirmware.org> on behalf of Raghu Krishnamurthy via TF-A <tf-a(a)lists.trustedfirmware.org> Sent: 06 April 2020 19:51 To: tf-a(a)lists.trustedfirmware.org <tf-a(a)lists.trustedfirmware.org> Subject: Re: [TF-A] fconf: Validating config data Thanks Louis. This new terminology helps. Let me spell this out again just to make sure we're on the same page. The following are the cases: 1) Mandatory Property hit, nodes are structurally correct - Works normally. 2) Mandatory Property hit, nodes are structurally *incorrect* - Asserts should catch structural issues during development because system integrator expected to not make mistakes with number of nodes etc. 3) Mandatory Property miss - Panic(). Why is this case causing a panic, but not case 2? You are allowing for some one to make the mistake of not having a mandatory property, but assume that if a mandatory property is present, it is always structurally sound. This is the part i have a problem with. In my view case 2 and case 3 should panic and code should not just assert on mandatory properties and must ALWAYS check for structural soundness of an FDT property. Similarly there are 3 cases for optional properties. My question: Why does case 3 panic, but not case 2 ? It sounds like your assumption is that case 2 cannot happen. If case 2 cannot happen, i claim that case 3 cannot happen either. Let me know what you think! Thanks Raghu On 4/6/20 3:57 AM, Louis Mayencourt via TF-A wrote: > Hi Raghu, > > Let me try to clarify/reword my idea: > > We complete the fconf documentation with a binding document, which > defines the nodes that should be present in the config DTB to consider > it as valid/well-formed. The document contains two kinds of node: > > * mandatory (critical): the firmware can't proceed without this > information (example: load address, image UUID, ...). If this node > is not present in the DTS, the build fails and/or the code panic. > > * optional (no-critical): the firmware can assume or assign a default > value and proceed (example: uart config, enable authentication flag, > ...). Such a property is used to influence the default behavior of > the firmware. > > />> This is non-deterministic failure./ > The miss of a mandatory (critical) node will always lead to a build > failure / code panic. > The miss of an optional (no-critical) node should not influence the > default behavior of the firmware. > > />> Is it not confusing to make the assumption that a DTB is "well > formed",i.e expect the build process/integrator to not mess up the >>> structure or number of nodes but allow the same integrator to miss a critical property in the DTB?/ > A DTB with a missing mandatory (critical) property should not be > considered well formed. > > />> If there is a missing critical property, is that not a badly formed > DTB?/ > With the above definition, it is. > > />> And if so, why not check for badly formed DTB's uniformly in code > and why only check for missing "critical" properties?/ > With the rewording of "critical" / "no-critical" to "mandatory" / > "optional", I think the situation is clearer: A DTB with a missing > "optional" node/property is is still considered well-formed. > > I hope I answered your questions and clarify the idea behind the design. > > regards, > Louis > > ------------------------------------------------------------------------ > *From:* Raghu Krishnamurthy <raghu.ncstate(a)icloud.com> > *Sent:* 05 April 2020 00:06 > *To:* Louis Mayencourt <Louis.Mayencourt(a)arm.com> > *Subject:* Re: [TF-A] fconf: Validating config data > Thanks Louis. > >>you can imagine a well-formed DTB which contain a > >>critical set of properties and can contain some optional properties. > > This makes things even more confusing. The assumption we are asking code > to make is that the DTB is always "well formed", ie don't check for > structural issues such as extra nodes etc, but we are still making the > distinctions between critical and non-critical properties, that may or > may not exist in the DTB, which may or may not cause a panic. This is > non-deterministic failure. > Is it not confusing to make the assumption that a DTB is "well > formed",i.e expect the build process/integrator to not mess up the > structure or number of nodes but allow the same integrator to miss a > critical property in the DTB? If there is a missing critical property, > is that not a badly formed DTB ? And if so, why not check for badly > formed DTB's uniformly in code and why only check for missing "critical" > properties? > > -Raghu > > On 4/3/20 3:16 AM, Louis Mayencourt wrote: >> Hi Raghu, >> >> I do agree that we need something similar to a binding document for >> fconf properties. (similar to >> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3694/2/docs/…). > >> At least for the common properties. >> >> The main idea behind the return code of the populator function was to >> allow the code to handle no-critical property misses or to handle >> critical failure by calling a platform hook. >> With this in mind, you can imagine a well-formed DTB which contain a >> critical set of properties and can contain some optional properties. The >> return code and the populator "name" / "config" can be used to handle >> this two cases. >> >> I tried to keep the design of fconf really simple, to leave room for >> improvement according to feedbacks. Thanks for helping improving it! >> >> Regards, >> Louis >> ------------------------------------------------------------------------ >> *From:* TF-A <tf-a-bounces(a)lists.trustedfirmware.org> on behalf of Raghu >> Krishnamurthy via TF-A <tf-a(a)lists.trustedfirmware.org> >> *Sent:* 03 April 2020 10:15 >> *To:* tf-a(a)lists.trustedfirmware.org <tf-a(a)lists.trustedfirmware.org> >> *Subject:* Re: [TF-A] fconf: Validating config data >> A further point is that the fconf populators return an error code and >> panics on error today. But if we are making the assumption that the >> DTB's are well formed, do we really need to fail or even return an error >> code? >> >> -Raghu >> >> On 4/3/20 1:51 AM, Raghu Krishnamurthy via TF-A wrote: >>> Hi All, (Sorry for the long email) >>> >>> The review >>> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3845 >>> attempts to fix bounds check in the fconf populator code for the >>> topology and SP's. During review, Sandrine thoughtfully pointed out that >>> there were discussions around bounds check along the same lines in the >>> review >>> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3492 and >>> it was deemed sufficient to have assertions in code and it was safe to >>> make the assumption that the DTB is always well formed and contains >>> valid values. I think this email mostly echoes Sandrine's concern from >>> review 3492. >>> >>> While i agree with the assumptions, I am generally of the opinion that >>> we should validate/range-check any data, even if it is signed. Being >>> signed does not necessarily mean the data is well formed/valid. If there >>> is a mistake in the build process and it is validly signed, it is >>> possible that we silently corrupt state/data that could later be used to >>> exploit firmware and/or make debugging hard. This is probably far >>> fetched, but the cost of adding the check is trivial to avoid this >>> possibility. >>> >>> I imagine the case where you have secure partitions signed by different >>> entity other than the silicon provider(dual root-of-trust). A silicon >>> provider provides a dev system for the SP provider to test and validate >>> the SP's on silicon. The silicon has production firmware(and hence no >>> assertions), but loads signed data from the SP provider which has some >>> invalid values. There could be silent corruption without any indication >>> whatsoever about what went wrong and it may be hard to debug if/when >>> there are issues. >>> Also, testing does not necessarily catch all invalid values since you >>> will likely not get 100% coverage, given the number of config options >>> available. Moreover, the code today, is not consistent in asserting on >>> every property for valid values and the failure mode is not >>> consistent/deterministic. It seems like every config option should have >>> a list of valid values or a range of acceptable values that must be at a >>> minimum asserted on. >>> I also wouldn't discount platforms such as RPI, where TRUSTED_BOARD_BOOT >>> is likely to be turned off since it really does not provide any >>> security, so assuming we always have signed data might not be valid. >>> >>> Anyway, is this decision worth revisiting? Too paranoid perhaps? :P >>> >>> >>> Thanks >>> Raghu >> -- >> TF-A mailing list >> TF-A(a)lists.trustedfirmware.org >> https://lists.trustedfirmware.org/mailman/listinfo/tf-a >> IMPORTANT NOTICE: The contents of this email and any attachments are >> confidential and may also be privileged. If you are not the intended >> recipient, please notify the sender immediately and do not disclose the >> contents to any other person, use it for any purpose, or store or copy >> the information in any medium. Thank you. > IMPORTANT NOTICE: The contents of this email and any attachments are > confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy > the information in any medium. Thank you. > -- TF-A mailing list TF-A(a)lists.trustedfirmware.org https://lists.trustedfirmware.org/mailman/listinfo/tf-a IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

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Re: [TF-A] fconf: Validating config data

by Raghu Krishnamurthy

Thanks Louis. This new terminology helps. Let me spell this out again just to make sure we're on the same page. The following are the cases: 1) Mandatory Property hit, nodes are structurally correct - Works normally. 2) Mandatory Property hit, nodes are structurally *incorrect* - Asserts should catch structural issues during development because system integrator expected to not make mistakes with number of nodes etc. 3) Mandatory Property miss - Panic(). Why is this case causing a panic, but not case 2? You are allowing for some one to make the mistake of not having a mandatory property, but assume that if a mandatory property is present, it is always structurally sound. This is the part i have a problem with. In my view case 2 and case 3 should panic and code should not just assert on mandatory properties and must ALWAYS check for structural soundness of an FDT property. Similarly there are 3 cases for optional properties. My question: Why does case 3 panic, but not case 2 ? It sounds like your assumption is that case 2 cannot happen. If case 2 cannot happen, i claim that case 3 cannot happen either. Let me know what you think! Thanks Raghu On 4/6/20 3:57 AM, Louis Mayencourt via TF-A wrote: > Hi Raghu, > > Let me try to clarify/reword my idea: > > We complete the fconf documentation with a binding document, which > defines the nodes that should be present in the config DTB to consider > it as valid/well-formed. The document contains two kinds of node: > > * mandatory (critical): the firmware can't proceed without this > information (example: load address, image UUID, ...). If this node > is not present in the DTS, the build fails and/or the code panic. > > * optional (no-critical): the firmware can assume or assign a default > value and proceed (example: uart config, enable authentication flag, > ...). Such a property is used to influence the default behavior of > the firmware. > > />> This is non-deterministic failure./ > The miss of a mandatory (critical) node will always lead to a build > failure / code panic. > The miss of an optional (no-critical) node should not influence the > default behavior of the firmware. > > />> Is it not confusing to make the assumption that a DTB is "well > formed",i.e expect the build process/integrator to not mess up the >>> structure or number of nodes but allow the same integrator to miss a critical property in the DTB?/ > A DTB with a missing mandatory (critical) property should not be > considered well formed. > > />> If there is a missing critical property, is that not a badly formed > DTB?/ > With the above definition, it is. > > />> And if so, why not check for badly formed DTB's uniformly in code > and why only check for missing "critical" properties?/ > With the rewording of "critical" / "no-critical" to "mandatory" / > "optional", I think the situation is clearer: A DTB with a missing > "optional" node/property is is still considered well-formed. > > I hope I answered your questions and clarify the idea behind the design. > > regards, > Louis > > ------------------------------------------------------------------------ > *From:* Raghu Krishnamurthy <raghu.ncstate(a)icloud.com> > *Sent:* 05 April 2020 00:06 > *To:* Louis Mayencourt <Louis.Mayencourt(a)arm.com> > *Subject:* Re: [TF-A] fconf: Validating config data > Thanks Louis. > >>you can imagine a well-formed DTB which contain a > >>critical set of properties and can contain some optional properties. > > This makes things even more confusing. The assumption we are asking code > to make is that the DTB is always "well formed", ie don't check for > structural issues such as extra nodes etc, but we are still making the > distinctions between critical and non-critical properties, that may or > may not exist in the DTB, which may or may not cause a panic. This is > non-deterministic failure. > Is it not confusing to make the assumption that a DTB is "well > formed",i.e expect the build process/integrator to not mess up the > structure or number of nodes but allow the same integrator to miss a > critical property in the DTB? If there is a missing critical property, > is that not a badly formed DTB ? And if so, why not check for badly > formed DTB's uniformly in code and why only check for missing "critical" > properties? > > -Raghu > > On 4/3/20 3:16 AM, Louis Mayencourt wrote: >> Hi Raghu, >> >> I do agree that we need something similar to a binding document for >> fconf properties. (similar to >> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3694/2/docs/…). > >> At least for the common properties. >> >> The main idea behind the return code of the populator function was to >> allow the code to handle no-critical property misses or to handle >> critical failure by calling a platform hook. >> With this in mind, you can imagine a well-formed DTB which contain a >> critical set of properties and can contain some optional properties. The >> return code and the populator "name" / "config" can be used to handle >> this two cases. >> >> I tried to keep the design of fconf really simple, to leave room for >> improvement according to feedbacks. Thanks for helping improving it! >> >> Regards, >> Louis >> ------------------------------------------------------------------------ >> *From:* TF-A <tf-a-bounces(a)lists.trustedfirmware.org> on behalf of Raghu >> Krishnamurthy via TF-A <tf-a(a)lists.trustedfirmware.org> >> *Sent:* 03 April 2020 10:15 >> *To:* tf-a(a)lists.trustedfirmware.org <tf-a(a)lists.trustedfirmware.org> >> *Subject:* Re: [TF-A] fconf: Validating config data >> A further point is that the fconf populators return an error code and >> panics on error today. But if we are making the assumption that the >> DTB's are well formed, do we really need to fail or even return an error >> code? >> >> -Raghu >> >> On 4/3/20 1:51 AM, Raghu Krishnamurthy via TF-A wrote: >>> Hi All, (Sorry for the long email) >>> >>> The review >>> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3845 >>> attempts to fix bounds check in the fconf populator code for the >>> topology and SP's. During review, Sandrine thoughtfully pointed out that >>> there were discussions around bounds check along the same lines in the >>> review >>> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3492 and >>> it was deemed sufficient to have assertions in code and it was safe to >>> make the assumption that the DTB is always well formed and contains >>> valid values. I think this email mostly echoes Sandrine's concern from >>> review 3492. >>> >>> While i agree with the assumptions, I am generally of the opinion that >>> we should validate/range-check any data, even if it is signed. Being >>> signed does not necessarily mean the data is well formed/valid. If there >>> is a mistake in the build process and it is validly signed, it is >>> possible that we silently corrupt state/data that could later be used to >>> exploit firmware and/or make debugging hard. This is probably far >>> fetched, but the cost of adding the check is trivial to avoid this >>> possibility. >>> >>> I imagine the case where you have secure partitions signed by different >>> entity other than the silicon provider(dual root-of-trust). A silicon >>> provider provides a dev system for the SP provider to test and validate >>> the SP's on silicon. The silicon has production firmware(and hence no >>> assertions), but loads signed data from the SP provider which has some >>> invalid values. There could be silent corruption without any indication >>> whatsoever about what went wrong and it may be hard to debug if/when >>> there are issues. >>> Also, testing does not necessarily catch all invalid values since you >>> will likely not get 100% coverage, given the number of config options >>> available. Moreover, the code today, is not consistent in asserting on >>> every property for valid values and the failure mode is not >>> consistent/deterministic. It seems like every config option should have >>> a list of valid values or a range of acceptable values that must be at a >>> minimum asserted on. >>> I also wouldn't discount platforms such as RPI, where TRUSTED_BOARD_BOOT >>> is likely to be turned off since it really does not provide any >>> security, so assuming we always have signed data might not be valid. >>> >>> Anyway, is this decision worth revisiting? Too paranoid perhaps? :P >>> >>> >>> Thanks >>> Raghu >> -- >> TF-A mailing list >> TF-A(a)lists.trustedfirmware.org >> https://lists.trustedfirmware.org/mailman/listinfo/tf-a >> IMPORTANT NOTICE: The contents of this email and any attachments are >> confidential and may also be privileged. If you are not the intended >> recipient, please notify the sender immediately and do not disclose the >> contents to any other person, use it for any purpose, or store or copy >> the information in any medium. Thank you. > IMPORTANT NOTICE: The contents of this email and any attachments are > confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy > the information in any medium. Thank you. >

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Re: [TF-A] fconf: Validating config data

by Louis Mayencourt

Hi Raghu, Let me try to clarify/reword my idea: We complete the fconf documentation with a binding document, which defines the nodes that should be present in the config DTB to consider it as valid/well-formed. The document contains two kinds of node: * mandatory (critical): the firmware can't proceed without this information (example: load address, image UUID, ...). If this node is not present in the DTS, the build fails and/or the code panic. * optional (no-critical): the firmware can assume or assign a default value and proceed (example: uart config, enable authentication flag, ...). Such a property is used to influence the default behavior of the firmware. >> This is non-deterministic failure. The miss of a mandatory (critical) node will always lead to a build failure / code panic. The miss of an optional (no-critical) node should not influence the default behavior of the firmware. >> Is it not confusing to make the assumption that a DTB is "well formed",i.e expect the build process/integrator to not mess up the >> structure or number of nodes but allow the same integrator to miss a critical property in the DTB? A DTB with a missing mandatory (critical) property should not be considered well formed. >> If there is a missing critical property, is that not a badly formed DTB? With the above definition, it is. >> And if so, why not check for badly formed DTB's uniformly in code and why only check for missing "critical" properties? With the rewording of "critical" / "no-critical" to "mandatory" / "optional", I think the situation is clearer: A DTB with a missing "optional" node/property is is still considered well-formed. I hope I answered your questions and clarify the idea behind the design. regards, Louis ________________________________ From: Raghu Krishnamurthy <raghu.ncstate(a)icloud.com> Sent: 05 April 2020 00:06 To: Louis Mayencourt <Louis.Mayencourt(a)arm.com> Subject: Re: [TF-A] fconf: Validating config data Thanks Louis. >>you can imagine a well-formed DTB which contain a >>critical set of properties and can contain some optional properties. This makes things even more confusing. The assumption we are asking code to make is that the DTB is always "well formed", ie don't check for structural issues such as extra nodes etc, but we are still making the distinctions between critical and non-critical properties, that may or may not exist in the DTB, which may or may not cause a panic. This is non-deterministic failure. Is it not confusing to make the assumption that a DTB is "well formed",i.e expect the build process/integrator to not mess up the structure or number of nodes but allow the same integrator to miss a critical property in the DTB? If there is a missing critical property, is that not a badly formed DTB ? And if so, why not check for badly formed DTB's uniformly in code and why only check for missing "critical" properties? -Raghu On 4/3/20 3:16 AM, Louis Mayencourt wrote: > Hi Raghu, > > I do agree that we need something similar to a binding document for > fconf properties. (similar to > https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3694/2/docs/…). > At least for the common properties. > > The main idea behind the return code of the populator function was to > allow the code to handle no-critical property misses or to handle > critical failure by calling a platform hook. > With this in mind, you can imagine a well-formed DTB which contain a > critical set of properties and can contain some optional properties. The > return code and the populator "name" / "config" can be used to handle > this two cases. > > I tried to keep the design of fconf really simple, to leave room for > improvement according to feedbacks. Thanks for helping improving it! > > Regards, > Louis > ------------------------------------------------------------------------ > *From:* TF-A <tf-a-bounces(a)lists.trustedfirmware.org> on behalf of Raghu > Krishnamurthy via TF-A <tf-a(a)lists.trustedfirmware.org> > *Sent:* 03 April 2020 10:15 > *To:* tf-a(a)lists.trustedfirmware.org <tf-a(a)lists.trustedfirmware.org> > *Subject:* Re: [TF-A] fconf: Validating config data > A further point is that the fconf populators return an error code and > panics on error today. But if we are making the assumption that the > DTB's are well formed, do we really need to fail or even return an error > code? > > -Raghu > > On 4/3/20 1:51 AM, Raghu Krishnamurthy via TF-A wrote: >> Hi All, (Sorry for the long email) >> >> The review >> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3845 >> attempts to fix bounds check in the fconf populator code for the >> topology and SP's. During review, Sandrine thoughtfully pointed out that >> there were discussions around bounds check along the same lines in the >> review >> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3492 and >> it was deemed sufficient to have assertions in code and it was safe to >> make the assumption that the DTB is always well formed and contains >> valid values. I think this email mostly echoes Sandrine's concern from >> review 3492. >> >> While i agree with the assumptions, I am generally of the opinion that >> we should validate/range-check any data, even if it is signed. Being >> signed does not necessarily mean the data is well formed/valid. If there >> is a mistake in the build process and it is validly signed, it is >> possible that we silently corrupt state/data that could later be used to >> exploit firmware and/or make debugging hard. This is probably far >> fetched, but the cost of adding the check is trivial to avoid this >> possibility. >> >> I imagine the case where you have secure partitions signed by different >> entity other than the silicon provider(dual root-of-trust). A silicon >> provider provides a dev system for the SP provider to test and validate >> the SP's on silicon. The silicon has production firmware(and hence no >> assertions), but loads signed data from the SP provider which has some >> invalid values. There could be silent corruption without any indication >> whatsoever about what went wrong and it may be hard to debug if/when >> there are issues. >> Also, testing does not necessarily catch all invalid values since you >> will likely not get 100% coverage, given the number of config options >> available. Moreover, the code today, is not consistent in asserting on >> every property for valid values and the failure mode is not >> consistent/deterministic. It seems like every config option should have >> a list of valid values or a range of acceptable values that must be at a >> minimum asserted on. >> I also wouldn't discount platforms such as RPI, where TRUSTED_BOARD_BOOT >> is likely to be turned off since it really does not provide any >> security, so assuming we always have signed data might not be valid. >> >> Anyway, is this decision worth revisiting? Too paranoid perhaps? :P >> >> >> Thanks >> Raghu > -- > TF-A mailing list > TF-A(a)lists.trustedfirmware.org > https://lists.trustedfirmware.org/mailman/listinfo/tf-a > IMPORTANT NOTICE: The contents of this email and any attachments are > confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy > the information in any medium. Thank you. IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years

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Re: [TF-A] fconf: Validating config data

by Raghu Krishnamurthy

+tf-a list On 4/4/20 4:06 PM, Raghu Krishnamurthy wrote: > Thanks Louis. > >>you can imagine a well-formed DTB which contain a > >>critical set of properties and can contain some optional properties. > > This makes things even more confusing. The assumption we are asking code > to make is that the DTB is always "well formed", ie don't check for > structural issues such as extra nodes etc, but we are still making the > distinctions between critical and non-critical properties, that may or > may not exist in the DTB, which may or may not cause a panic. This is > non-deterministic failure. > Is it not confusing to make the assumption that a DTB is "well > formed",i.e expect the build process/integrator to not mess up the > structure or number of nodes but allow the same integrator to miss a > critical property in the DTB? If there is a missing critical property, > is that not a badly formed DTB ? And if so, why not check for badly > formed DTB's uniformly in code and why only check for missing "critical" > properties? > > -Raghu > > On 4/3/20 3:16 AM, Louis Mayencourt wrote: >> Hi Raghu, >> >> I do agree that we need something similar to a binding document for >> fconf properties. (similar to >> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3694/2/docs/…). >> At least for the common properties. >> >> The main idea behind the return code of the populator function was to >> allow the code to handle no-critical property misses or to handle >> critical failure by calling a platform hook. >> With this in mind, you can imagine a well-formed DTB which contain a >> critical set of properties and can contain some optional properties. >> The return code and the populator "name" / "config" can be used to >> handle this two cases. >> >> I tried to keep the design of fconf really simple, to leave room for >> improvement according to feedbacks. Thanks for helping improving it! >> >> Regards, >> Louis >> ------------------------------------------------------------------------ >> *From:* TF-A <tf-a-bounces(a)lists.trustedfirmware.org> on behalf of >> Raghu Krishnamurthy via TF-A <tf-a(a)lists.trustedfirmware.org> >> *Sent:* 03 April 2020 10:15 >> *To:* tf-a(a)lists.trustedfirmware.org <tf-a(a)lists.trustedfirmware.org> >> *Subject:* Re: [TF-A] fconf: Validating config data >> A further point is that the fconf populators return an error code and >> panics on error today. But if we are making the assumption that the >> DTB's are well formed, do we really need to fail or even return an error >> code? >> >> -Raghu >> >> On 4/3/20 1:51 AM, Raghu Krishnamurthy via TF-A wrote: >>> Hi All, (Sorry for the long email) >>> >>> The review >>> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3845 >>> attempts to fix bounds check in the fconf populator code for the >>> topology and SP's. During review, Sandrine thoughtfully pointed out >>> that there were discussions around bounds check along the same lines >>> in the review >>> https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3492 and >>> it was deemed sufficient to have assertions in code and it was safe >>> to make the assumption that the DTB is always well formed and >>> contains valid values. I think this email mostly echoes Sandrine's >>> concern from review 3492. >>> >>> While i agree with the assumptions, I am generally of the opinion >>> that we should validate/range-check any data, even if it is signed. >>> Being signed does not necessarily mean the data is well formed/valid. >>> If there is a mistake in the build process and it is validly signed, >>> it is possible that we silently corrupt state/data that could later >>> be used to exploit firmware and/or make debugging hard. This is >>> probably far fetched, but the cost of adding the check is trivial to >>> avoid this possibility. >>> >>> I imagine the case where you have secure partitions signed by >>> different entity other than the silicon provider(dual root-of-trust). >>> A silicon provider provides a dev system for the SP provider to test >>> and validate the SP's on silicon. The silicon has production >>> firmware(and hence no assertions), but loads signed data from the SP >>> provider which has some invalid values. There could be silent >>> corruption without any indication whatsoever about what went wrong >>> and it may be hard to debug if/when there are issues. >>> Also, testing does not necessarily catch all invalid values since you >>> will likely not get 100% coverage, given the number of config options >>> available. Moreover, the code today, is not consistent in asserting >>> on every property for valid values and the failure mode is not >>> consistent/deterministic. It seems like every config option should >>> have a list of valid values or a range of acceptable values that must >>> be at a minimum asserted on. >>> I also wouldn't discount platforms such as RPI, where >>> TRUSTED_BOARD_BOOT is likely to be turned off since it really does >>> not provide any security, so assuming we always have signed data >>> might not be valid. >>> >>> Anyway, is this decision worth revisiting? Too paranoid perhaps? :P >>> >>> >>> Thanks >>> Raghu >> -- >> TF-A mailing list >> TF-A(a)lists.trustedfirmware.org >> https://lists.trustedfirmware.org/mailman/listinfo/tf-a >> IMPORTANT NOTICE: The contents of this email and any attachments are >> confidential and may also be privileged. If you are not the intended >> recipient, please notify the sender immediately and do not disclose >> the contents to any other person, use it for any purpose, or store or >> copy the information in any medium. Thank you. >

5 years

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Re: [TF-A] Change in ...trusted-firmware-a[integration]: Check for out-of-bound accesses in the CoT description

by Sandrine Bailleux

Hi Raghu, On 4/3/20 1:38 AM, Raghu Krishnamurthy via TF-A wrote: > Thanks Sandrine. Patches look good. Thanks for the review! > I realized after looking at things a little closer that i had > misunderstood how fconf works for io policies. I thought the image id's > themselves came from the config files and not just the UUID's, which is > why i was worried about bounds check, since the id was coming from an > external source(trusted or untrusted, depending on if it is signed data > or not). > This also made me realize that we are using another table built into > code, to convert from image id to UUID for io policies. Is there a > reason image id's also can't be discovered from the config file? I remember some internal discussions around this topic a few weeks ago. If I recall correctly, the current thinking is that down the line, we would like to move image IDs to DTBs but this looks complicated to achieve today because image IDs are used by several components in TF-A to tie things together. More work would be needed to abstract this properly everywhere. I think other folks in the team (Olivier? Manish? Louis?) might be able to comment further on this. Regards, Sandrine IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

5 years

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Re: [TF-A] fconf: Validating config data

by Raghu Krishnamurthy

A further point is that the fconf populators return an error code and panics on error today. But if we are making the assumption that the DTB's are well formed, do we really need to fail or even return an error code? -Raghu On 4/3/20 1:51 AM, Raghu Krishnamurthy via TF-A wrote: > Hi All, (Sorry for the long email) > > The review > https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3845 > attempts to fix bounds check in the fconf populator code for the > topology and SP's. During review, Sandrine thoughtfully pointed out that > there were discussions around bounds check along the same lines in the > review > https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3492 and > it was deemed sufficient to have assertions in code and it was safe to > make the assumption that the DTB is always well formed and contains > valid values. I think this email mostly echoes Sandrine's concern from > review 3492. > > While i agree with the assumptions, I am generally of the opinion that > we should validate/range-check any data, even if it is signed. Being > signed does not necessarily mean the data is well formed/valid. If there > is a mistake in the build process and it is validly signed, it is > possible that we silently corrupt state/data that could later be used to > exploit firmware and/or make debugging hard. This is probably far > fetched, but the cost of adding the check is trivial to avoid this > possibility. > > I imagine the case where you have secure partitions signed by different > entity other than the silicon provider(dual root-of-trust). A silicon > provider provides a dev system for the SP provider to test and validate > the SP's on silicon. The silicon has production firmware(and hence no > assertions), but loads signed data from the SP provider which has some > invalid values. There could be silent corruption without any indication > whatsoever about what went wrong and it may be hard to debug if/when > there are issues. > Also, testing does not necessarily catch all invalid values since you > will likely not get 100% coverage, given the number of config options > available. Moreover, the code today, is not consistent in asserting on > every property for valid values and the failure mode is not > consistent/deterministic. It seems like every config option should have > a list of valid values or a range of acceptable values that must be at a > minimum asserted on. > I also wouldn't discount platforms such as RPI, where TRUSTED_BOARD_BOOT > is likely to be turned off since it really does not provide any > security, so assuming we always have signed data might not be valid. > > Anyway, is this decision worth revisiting? Too paranoid perhaps? :P > > > Thanks > Raghu

5 years

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fconf: Validating config data

by Raghu Krishnamurthy

Hi All, (Sorry for the long email) The review https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3845 attempts to fix bounds check in the fconf populator code for the topology and SP's. During review, Sandrine thoughtfully pointed out that there were discussions around bounds check along the same lines in the review https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/3492 and it was deemed sufficient to have assertions in code and it was safe to make the assumption that the DTB is always well formed and contains valid values. I think this email mostly echoes Sandrine's concern from review 3492. While i agree with the assumptions, I am generally of the opinion that we should validate/range-check any data, even if it is signed. Being signed does not necessarily mean the data is well formed/valid. If there is a mistake in the build process and it is validly signed, it is possible that we silently corrupt state/data that could later be used to exploit firmware and/or make debugging hard. This is probably far fetched, but the cost of adding the check is trivial to avoid this possibility. I imagine the case where you have secure partitions signed by different entity other than the silicon provider(dual root-of-trust). A silicon provider provides a dev system for the SP provider to test and validate the SP's on silicon. The silicon has production firmware(and hence no assertions), but loads signed data from the SP provider which has some invalid values. There could be silent corruption without any indication whatsoever about what went wrong and it may be hard to debug if/when there are issues. Also, testing does not necessarily catch all invalid values since you will likely not get 100% coverage, given the number of config options available. Moreover, the code today, is not consistent in asserting on every property for valid values and the failure mode is not consistent/deterministic. It seems like every config option should have a list of valid values or a range of acceptable values that must be at a minimum asserted on. I also wouldn't discount platforms such as RPI, where TRUSTED_BOARD_BOOT is likely to be turned off since it really does not provide any security, so assuming we always have signed data might not be valid. Anyway, is this decision worth revisiting? Too paranoid perhaps? :P Thanks Raghu

5 years

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