Re: [TF-M] [Question] FIH usage in platforms

Hi Ken,

“double-check every return value of sub-functions, this is really a burden when under developing” That’s exactly why FIH can help mitigate physical attacks. It adds redundant checks and increases the complexity in code to make it difficult for attackers. It of course also increase develop efforts and it is expected for physical attack mitigation.

Regarding tight schedule, it can be workaround by splitting the HAL API definitions with and without FIH enabled respectively.

Best regards, Hu Ziji

From: TF-M tf-m-bounces@lists.trustedfirmware.org On Behalf Of Ken Liu via TF-M Sent: Thursday, August 12, 2021 4:54 PM To: tf-m@lists.trustedfirmware.org Cc: nd nd@arm.com Subject: Re: [TF-M] [Question] FIH usage in platforms

Thanks, then we can do some planning and make the FIH feature online again before the deadline.

I do agree FIH needs an update. There would be reasons for HAL to change its implementation or prototype; and the existing FIH needs another copy of implementation, change the prototype a bit, and double-check every return value of sub-functions, this is really a burden when under developing: We first need to ensure the non-FIH version work, get reviewed; and then prepare the FIH version, get reviewed again. And, the platform owner may be afraid of changing the HAL implementation, as it is risky to do that.

I’d suggest enhancing the solution that: - Doing measurement without changing HAL API prototype.

As the bandwidth is always a problem, so I have to prioritize the designs. Let’s see if we can get help from people. Otherwise, I will allocate some effort after HAL update is done. This means, there would be a couple of HAL updates with no FIH support recently, and FIH version comes later.

Any volunteer is welcome.

/Ken

From: Michel JAOUEN <michel.jaouen@st.commailto:michel.jaouen@st.com> Sent: Thursday, August 12, 2021 4:39 PM To: David Hu <David.Hu@arm.commailto:David.Hu@arm.com>; Ken Liu <Ken.Liu@arm.commailto:Ken.Liu@arm.com> Cc: nd <nd@arm.commailto:nd@arm.com>; tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Subject: RE: [Question] FIH usage in platforms

Hello,

Next platform with FIH enabled is foreseen to be in V1.5.0 with FIH enabled (the pull request without FIH enabled is expected in september) FIH support is planned on later pull request. So FIH recovering needs to be done at least 3 weeks before V1.5.0 code freeze, to let the time to do adaptation/test /fix on this new platform.

Best Regards Michel

ST Restricted From: TF-M <tf-m-bounces@lists.trustedfirmware.orgmailto:tf-m-bounces@lists.trustedfirmware.org> On Behalf Of David Hu via TF-M Sent: jeudi 12 août 2021 10:34 To: Ken Liu <Ken.Liu@arm.commailto:Ken.Liu@arm.com>; tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Cc: nd <nd@arm.commailto:nd@arm.com> Subject: Re: [TF-M] [Question] FIH usage in platforms

Hi Ken,

Imho, it can be more reasonable to improve HAL and FIH API together, compared to removing existing security protection.

Best regards, Hu Ziji

From: TF-M <tf-m-bounces@lists.trustedfirmware.orgmailto:tf-m-bounces@lists.trustedfirmware.org> On Behalf Of Ken Liu via TF-M Sent: Thursday, August 12, 2021 4:26 PM To: tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Cc: nd <nd@arm.commailto:nd@arm.com> Subject: Re: [TF-M] [Question] FIH usage in platforms

Hi Michel,

Is there a rough timeline for the next stm platform? I can estimate if we got time to update or add it back. Besides that, curious if ST got test environments for FIH? If there are some then at least we have a method to evaluate the FIH effect.

BR.

/Ken

From: Michel JAOUEN <michel.jaouen@st.commailto:michel.jaouen@st.com> Sent: Thursday, August 12, 2021 4:21 PM To: Ken Liu <Ken.Liu@arm.commailto:Ken.Liu@arm.com> Cc: tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Subject: RE: [Question] FIH usage in platforms

Hello,

Regarding FIH feature, for stm next platform I consider FIH as key for Faul injection Mitigation, so the FIH is enabled for the next stm platform. Even if a platform gets certified without this FIH feature, other mitigations at platform level have been set to get certified. The benefits of FIH is to make the mitigation available for all platform, so I consider that maintaining it during development is important.

Best regards Michel

ST Restricted From: TF-M <tf-m-bounces@lists.trustedfirmware.orgmailto:tf-m-bounces@lists.trustedfirmware.org> On Behalf Of Ken Liu via TF-M Sent: mercredi 11 août 2021 07:24 To: tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Cc: nd <nd@arm.commailto:nd@arm.com> Subject: Re: [TF-M] [Question] FIH usage in platforms

Hi David,

This mail is seeking evidence about how FIH is effectively working. As the latest L3 certified device is still using v1.0-RC2, where the FIH is not supported in that codebase.

I assumed a pre-condition when “recovering back”: if FIH still can prove its importance. The FIH has to be enhanced before recovering back. FIH is a serious hardware feature so what software can do is limited. Delay and Double-check protection unit is the two easiest way can be applied. Other behaviors, as we can see, affect the development much, which makes it more proper to be done in toolchain instead of programming.

Compare with this complex but less used mechanism, we have prioritized features to be done. That is the reason why we need to do the feature development first instead of solving the development difficulty at the current stage.

Meanwhile, anyone proposing a better FIH mechanism is welcome – that would make the feature development and difficulty solving in parallel.

BR.

/Ken

From: David Hu <David.Hu@arm.commailto:David.Hu@arm.com> Sent: Wednesday, August 11, 2021 11:53 AM To: Ken Liu <Ken.Liu@arm.commailto:Ken.Liu@arm.com>; tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Cc: nd <nd@arm.commailto:nd@arm.com> Subject: RE: [Question] FIH usage in platforms

Hi Ken,

Based on your idea, several fundamental countermeasures against physical attacks will be removed.

* Double checking return value * Execution flow counters * Structured variables with initial failure values

Mitigation to physical attacks is required in PSA Level 3 certify. It is crucial for TF-M to provide reasonable physical attack mitigations. Please provide proper justifications to prove that removal of those countermeasures above won’t weaken existing protection against physical attacks.

On the other hand, even if those countermeasures above are removed now, it will still affect the HAL updates when they are “recovered back”. So why not solve the development difficulty at this moment?

Best regards, Hu Ziji

From: TF-M <tf-m-bounces@lists.trustedfirmware.orgmailto:tf-m-bounces@lists.trustedfirmware.org> On Behalf Of Ken Liu via TF-M Sent: Monday, August 9, 2021 10:18 AM To: tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org Cc: nd <nd@arm.commailto:nd@arm.com> Subject: [TF-M] [Question] FIH usage in platforms

Hi,

Is there anyone enables FIH when developing or releasing?

Background: We got a couple of HAL updates during feature development and found FIH affects the development progress much, as we need to provide two sets of prototypes and implementation for involved functions, this doubles the efforts on debugging or coding.

So a draft idea in my mind is to shut down part of the functionalities during this update stage and recover them back if FIH still can prove its importance later.

These functionalities are KEPT during the update stage: - FIH delay, which makes it harder to find the exact time point. - Protection unit validation, ensures the protection unit is initialized as expected.

Please provide your feedback about the usage and the idea. For platforms that are applying this feature, we need to find out a trade-off way.

Thanks.

/Ken