Hi Bohdan,

The sequence you provided seems reasonable, however "backend_abi_leaving_spm" and the subsequent "arch_release_sched_lock" execute with all interrupts disabled, so there are no interrupts that should change the scheduler_lock in between [1]. A pending interrupt would execute as soon as L:91, and then would correctly set the PendSV.

Can you please share a bit more about your interrupt configurations, priorities etc? Am I missing something else?

Thanks Best regards, Nick

[1] https://git.trustedfirmware.org/plugins/gitiles/TF-M/trusted-firmware-m.git/...

________________________________ From: Nicola Mazzucato via TF-M tf-m@lists.trustedfirmware.org Sent: 17 December 2025 08:37 To: tf-m@lists.trustedfirmware.org tf-m@lists.trustedfirmware.org; Bohdan.Hunko@infineon.com Bohdan.Hunko@infineon.com Cc: Ivan.Kozemchuk@infineon.com Ivan.Kozemchuk@infineon.com; Hennadiy.Kytsun@infineon.com Hennadiy.Kytsun@infineon.com Subject: [TF-M] Re: Race condition in SPM scheduler lock logic

Thanks Bohdan for reporting this.

Let me have a look and try to reproduce it.

Best regards, Nick

________________________________ From: Bohdan.Hunko--- via TF-M tf-m@lists.trustedfirmware.org Sent: 16 December 2025 20:54 To: tf-m@lists.trustedfirmware.org tf-m@lists.trustedfirmware.org Cc: Ivan.Kozemchuk@infineon.com Ivan.Kozemchuk@infineon.com; Hennadiy.Kytsun@infineon.com Hennadiy.Kytsun@infineon.com Subject: [TF-M] Race condition in SPM scheduler lock logic

Hi all,

I have found a bug in SPM scheduler lock logic – this bug is extremely hard to reproduce as it requires precise conditions and timings, but here is the description of the bug scenario:

1. Partition A calls psa_wait to wait for a signal (this signal is going to be asserted by FLIH IRQ later) 2. Currently signal is not asserted, no other partition is runnable, thus SPM marks this signal as being awaited and then schedules idle_thread 3. idle_thread calls psa_wait to poll SPM * psa_wait calls tfm_arch_thread_fn_call * tfm_arch_thread_fn_call calls backend_abi_entering_spm * backend_abi_entering_spm calls arch_acquire_sched_lock * arch_acquire_sched_lock sets scheduler_lock = SCHEDULER_LOCKED * psa_wait (called by idle_partition) is being processed up to the point of backend_abi_leaving_spm * backend_abi_leaving_spm calls arch_release_sched_lock * here is where very sneaky the bug happens * arch_release_sched_lock executes following assembly instructions

i. "ldr r1, =scheduler_lock \n" "ldr r0, [r1, #0] \n"

ii. At this point r0 holds scheduler_lock is = SCHEDULER_LOCKED

iii. After these instructions are executed FLIH interrupt arrives

* FLIH handler asserts signal (which should unblock execution of the Partition A) * spm_handle_interrupt calls backend_assert_signal * backend_assert_signal does if (p_pt->signals_asserted & p_pt->signals_waiting) and returns STATUS_NEED_SCHEDULE * spm_handle_interrupt calls arch_attempt_schedule * arch_attempt_schedule checks value of scheduler_lock (which is SCHEDULER_LOCKED) and sets scheduler_lock= SCHEDULER_ATTEMPTED * Interrupt returns

iv. Execution continues, now scheduler_lock is = SCHEDULER_ATTEMPTED But the next line of code in arch_release_sched_lock is "movs r2, #"M2S(SCHEDULER_UNLOCKED)" \n"/* Unlock scheduler */

This effectively overwrites scheduler_lock from SCHEDULER_ATTEMPTED to SCHEDULER_UNLOCKED This means that following SRM scheduling logic will not trigger PendSV and just return to idle_partition – effectively resulting in a hang of a system.

Looks like the solution is to wrap lock logic in critical section. But may be there is other things that can be done to better fix this issue.

Let me know if there are other details that may be helpful to fix this bug.

Bohdan Hunko

Cypress Semiconductor Ukraine LLC

Senior Engineer

CSS ICW SW INT BFS SFW

Mobile: +380995019714 Bohdan.Hunko@infineon.commailto:Bohdan.Hunko@infineon.com

Thank you Bohdan,

I am still a bit confused about the setup, because that section in SPM always executes in privileged execution. If the calling partition is not privileged, then the SVC handler will take place to elevate execution.

Thanks Best regards, Nick

________________________________ From: Bohdan.Hunko@infineon.com Bohdan.Hunko@infineon.com Sent: 19 December 2025 10:31 To: Nicola Mazzucato Nicola.Mazzucato@arm.com Cc: Ivan.Kozemchuk@infineon.com Ivan.Kozemchuk@infineon.com; Hennadiy.Kytsun@infineon.com Hennadiy.Kytsun@infineon.com; tf-m@lists.trustedfirmware.org tf-m@lists.trustedfirmware.org Subject: RE: Race condition in SPM scheduler lock logic

Hi Nicola,

* Can you please share a bit more about your interrupt configurations, priorities etc?

We don’t do anything special, the IRQ priority is Normal, nothing unusual.

* Am I missing something else?

Looking into the code one thing that comes to mind is that tfm_arch_thread_fn_call can be called from unprivileged partition thus interrupt masking will not take effect. I believe this explains the behavior described in previous mail.

If so then not only this code is effected, but other multithread issues may occur in different places of tfm_arch_thread_fn_call.

Bohdan Hunko

Cypress Semiconductor Ukraine LLC

Senior Engineer

CSS ICW SW INT BFS SFW

Mobile: +380995019714 Bohdan.Hunko@infineon.commailto:Bohdan.Hunko@infineon.com

From: Nicola Mazzucato Nicola.Mazzucato@arm.com Sent: Friday, 19 December 2025 11:59 To: Hunko Bohdan (CSS ICW SW INT BFS SFW) Bohdan.Hunko@infineon.com Cc: Kozemchuk Ivan (CSS ICW SW INT BFS SFW) Ivan.Kozemchuk@infineon.com; Kytsun Hennadiy (CSS ICW SW INT BFS SFW) Hennadiy.Kytsun@infineon.com; Anton Komlev via TF-M tf-m@lists.trustedfirmware.org Subject: Re: Race condition in SPM scheduler lock logic

Caution: This e-mail originated outside Infineon Technologies. Please be cautious when sharing information or opening attachments especially from unknown senders. Refer to our intranet guidehttps://intranet-content.infineon.com/explore/aboutinfineon/rules/informationsecurity/ug/SocialEngineering/Pages/SocialEngineeringElements_en.aspx to help you identify Phishing email.

Hi Bohdan,

The sequence you provided seems reasonable, however "backend_abi_leaving_spm" and the subsequent "arch_release_sched_lock" execute with all interrupts disabled, so there are no interrupts that should change the scheduler_lock in between [1].

A pending interrupt would execute as soon as L:91, and then would correctly set the PendSV.

Can you please share a bit more about your interrupt configurations, priorities etc?

Am I missing something else?

Thanks

Best regards,

Nick

[1]

https://git.trustedfirmware.org/plugins/gitiles/TF-M/trusted-firmware-m.git/...

________________________________

From: Nicola Mazzucato via TF-M <tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org> Sent: 17 December 2025 08:37 To: tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org <tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org>; Bohdan.Hunko@infineon.commailto:Bohdan.Hunko@infineon.com <Bohdan.Hunko@infineon.commailto:Bohdan.Hunko@infineon.com> Cc: Ivan.Kozemchuk@infineon.commailto:Ivan.Kozemchuk@infineon.com <Ivan.Kozemchuk@infineon.commailto:Ivan.Kozemchuk@infineon.com>; Hennadiy.Kytsun@infineon.commailto:Hennadiy.Kytsun@infineon.com <Hennadiy.Kytsun@infineon.commailto:Hennadiy.Kytsun@infineon.com> Subject: [TF-M] Re: Race condition in SPM scheduler lock logic

Thanks Bohdan for reporting this.

Let me have a look and try to reproduce it.

Best regards,

Nick

________________________________

From: Bohdan.Hunko--- via TF-M <tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org> Sent: 16 December 2025 20:54 To: tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org <tf-m@lists.trustedfirmware.orgmailto:tf-m@lists.trustedfirmware.org> Cc: Ivan.Kozemchuk@infineon.commailto:Ivan.Kozemchuk@infineon.com <Ivan.Kozemchuk@infineon.commailto:Ivan.Kozemchuk@infineon.com>; Hennadiy.Kytsun@infineon.commailto:Hennadiy.Kytsun@infineon.com <Hennadiy.Kytsun@infineon.commailto:Hennadiy.Kytsun@infineon.com> Subject: [TF-M] Race condition in SPM scheduler lock logic

Hi all,

I have found a bug in SPM scheduler lock logic – this bug is extremely hard to reproduce as it requires precise conditions and timings, but here is the description of the bug scenario:

1. Partition A calls psa_wait to wait for a signal (this signal is going to be asserted by FLIH IRQ later) 2. Currently signal is not asserted, no other partition is runnable, thus SPM marks this signal as being awaited and then schedules idle_thread 3. idle_thread calls psa_wait to poll SPM

* psa_wait calls tfm_arch_thread_fn_call * tfm_arch_thread_fn_call calls backend_abi_entering_spm * backend_abi_entering_spm calls arch_acquire_sched_lock * arch_acquire_sched_lock sets scheduler_lock = SCHEDULER_LOCKED * psa_wait (called by idle_partition) is being processed up to the point of backend_abi_leaving_spm * backend_abi_leaving_spm calls arch_release_sched_lock * here is where very sneaky the bug happens * arch_release_sched_lock executes following assembly instructions

i. "ldr r1, =scheduler_lock \n" "ldr r0, [r1, #0] \n"

ii. At this point r0 holds scheduler_lock is = SCHEDULER_LOCKED

iii. After these instructions are executed FLIH interrupt arrives

* FLIH handler asserts signal (which should unblock execution of the Partition A) * spm_handle_interrupt calls backend_assert_signal * backend_assert_signal does if (p_pt->signals_asserted & p_pt->signals_waiting) and returns STATUS_NEED_SCHEDULE * spm_handle_interrupt calls arch_attempt_schedule * arch_attempt_schedule checks value of scheduler_lock (which is SCHEDULER_LOCKED) and sets scheduler_lock= SCHEDULER_ATTEMPTED * Interrupt returns

iv. Execution continues, now scheduler_lock is = SCHEDULER_ATTEMPTED But the next line of code in arch_release_sched_lock is "movs r2, #"M2S(SCHEDULER_UNLOCKED)" \n"/* Unlock scheduler */

This effectively overwrites scheduler_lock from SCHEDULER_ATTEMPTED to SCHEDULER_UNLOCKED This means that following SRM scheduling logic will not trigger PendSV and just return to idle_partition – effectively resulting in a hang of a system.

Looks like the solution is to wrap lock logic in critical section. But may be there is other things that can be done to better fix this issue.

Let me know if there are other details that may be helpful to fix this bug.

Bohdan Hunko

Cypress Semiconductor Ukraine LLC

Senior Engineer

CSS ICW SW INT BFS SFW

Mobile: +380995019714 Bohdan.Hunko@infineon.commailto:Bohdan.Hunko@infineon.com

Hi Ronan,

I think you may need to add -DPSA_ARCH_TESTS_PATH=<absolute-path-to-psa-arch-tests> to your build command.

Hope that helps, Best regards, Nick

________________________________ From: Ronan GABOU via TF-M tf-m@lists.trustedfirmware.org Sent: 22 December 2025 15:19 To: tf-m@lists.trustedfirmware.org tf-m@lists.trustedfirmware.org Subject: [TF-M] : PSA API test build issue on main branch TFM

Hello All,

I wanted to run regression and PSA API tests before Upstreaming ST patches to community.

However I had issue with PSA API tests.

Note, that I can build Regression tests without any problem.

I use the main branch and latest SHA1

I ‘ve the following error:

$ build_L56_psa_gnu_s

-- The C compiler identification is GNU 15.2.0

CMake Error at C:/TFM_L56/tf-m-tests/tests_psa_arch/fetch_repo/CMakeLists.txt:10 (include):

include could not find requested file:

remote_library

CMake Error at C:/TFM_L56/tf-m-tests/tests_psa_arch/fetch_repo/CMakeLists.txt:15 (fetch_remote_library):

Unknown CMake command "fetch_remote_library".

-- Configuring incomplete, errors occurred!

ninja: error: loading 'build.ninja': The system cannot find the file specified.

The cmake command is :

cmake -S $TFM_work_dir_L56/tf-m-tests/tests_psa_arch/spe -B $L56_build_s -GNinja -DTFM_PLATFORM=stm/stm32l562e_dk -DTFM_TOOLCHAIN_FILE=$L56_tfm_src/toolchain_GNUARM.cmake -DCONFIG_TFM_SOURCE_PATH=$L56_tfm_src -DTFM_PSA_API=ON -DTEST_PSA_API=PROTECTED_STORAGE;

c:\TFM_L56\tf-m-tests\tests_psa_arch\fetch_repo\CMakeLists.txt content is :

include(remote_library)

set(PSA_ARCH_TESTS_PATH "DOWNLOAD" CACHE PATH "Path to PSA arch test repository used for SPE build")

set(PSA_ARCH_TESTS_VERSION "v24.03_API1.6_CRYPTO_1.1.0" CACHE STRING "The version of PSA arch tests to use")

fetch_remote_library(

LIB_NAME psa_arch_tests

LIB_SOURCE_PATH_VAR PSA_ARCH_TESTS_PATH

LIB_BASE_DIR ${CMAKE_BINARY_DIR}/fetch_repo

LIB_PATCH_DIR ${CMAKE_CURRENT_LIST_DIR}

LIB_FORCE_PATCH PSA_ARCH_TESTS_FORCE_PATCH

FETCH_CONTENT_ARGS

GIT_REPOSITORY https://github.com/ARM-software/psa-arch-tests.git

GIT_TAG ${PSA_ARCH_TESTS_VERSION}

GIT_SHALLOW TRUE

GIT_PROGRESS TRUE

)

Note In case I use v2.1.3 TFM tag with associated tf-m-tests and mcuboot SHA1 I can build the PSA API binaries without this error.

Does someone can provide me ideas / tracks to solve my problem?

Thank you for your time, Ronan,

[Shape, rectangle Description automatically generated]

Ronan GABOU | Tel: +33 1 58 07 80 19

MDG / General Purpose Microcontroller Sub-Group / Wireless Business Line / Cellular

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