StrongBox op-counter leak breaks banking apps on Android 16 / StrongBox devices (upstream TEESimulator-RS) — please pull fix

[tastitalia-robertoc]

Summary

AlwaysStrong (which bundles TEESimulator-RS) breaks all StrongBox-backed apps on
devices that have a real StrongBox secure element running Android 16.

The root cause is in the bundled TEESimulator-RS, not in the PIF part, so I
filed the detailed report upstream:
➡️ Enginex0/TEESimulator-RS#49

Short description

On a device with a real StrongBox (NXP JavaCard), TEESimulator forwards the
StrongBox createOperation to the HAL, the operation finish completes
successfully on hardware, but the per-UID StrongBox operation counter is never
released. It accumulates to hw=4 / max=4 and then rejects everything with
StrongBox op limit reached → the app gets KeyStoreException -29 TOO_MANY_OPERATIONS. This happens globally, even for apps NOT in
target.txt, so excluding an app from the GUI does not help.

Result: apps work on first launch (fresh data) and fail on second launch when
they must decrypt their keychain.

Environment

• AlwaysStrong 1.0.3 (also reproduced with standalone TEESimulator-RS v6.0.1-307 + separate PIF)
• POCO F8 Ultra (myron) and POCO F8 Pro (annibale) — xiaomi.eu HyperOS 3, Android 16

[evoker0]

Read both upstream issues (#39 and #49) and the code they quote. Confirming your diagnosis, with one correction: it isn't a leaked counter. The limiter is window based:

STRONGBOX_MAX_CONCURRENT_OPS = 4
STRONGBOX_OP_WINDOW_NS = 10_000_000_000L  // 10s

So it's really 4 ops per 10 seconds, while real StrongBox allows 4 concurrent ops. There is no counter to release, entries just age out after 10s. An app doing 5 legitimate decrypts in a row trips it even though the hardware would have been fine.

The second half is the one that matters here: trackAndEnforceOpLimit() is called in the Domain.KEY_ID not-found branch, before forwarding to the real HAL. A limiter meant for synthetic keys is applied to real hardware keys, which is why removing an app from target.txt changes nothing.

On our side there is nothing to fix, and nothing to pull yet. Upstream state:

• #46 (skip the limit for forwarded HAL ops) is the correct fix, open since July, not merged
• #50 and #52 closed without merging, #54 still open
• latest release is v6.0.1-307 (11 Jul), older than all of them

AlwaysStrong pins v6.0.1-307, so the bug ships with us. As soon as a fix is merged and released upstream we bump the pin and cut a build. Until then the only workaround is the one you found, dropping android.hardware.strongbox_keystore so apps fall back to TEE, at the cost of losing StrongBox everywhere.

Keeping this open to track it. Thanks for the writeup, it's the clearest report we've had.