From: Yeoreum Yun yeoreum.yun@arm.com
[ Upstream commit 0e0546eabcd6c19765a8dbf5b5db3723e7b0ea75 ]
The Linux IMA (Integrity Measurement Architecture) subsystem used for secure boot, file integrity, or remote attestation cannot be a loadable module for few reasons listed below:
o Boot-Time Integrity: IMA’s main role is to measure and appraise files before they are used. This includes measuring critical system files during early boot (e.g., init, init scripts, login binaries). If IMA were a module, it would be loaded too late to cover those.
o TPM Dependency: IMA integrates tightly with the TPM to record measurements into PCRs. The TPM must be initialized early (ideally before init_ima()), which aligns with IMA being built-in.
o Security Model: IMA is part of a Trusted Computing Base (TCB). Making it a module would weaken the security model, as a potentially compromised system could delay or tamper with its initialization.
IMA must be built-in to ensure it starts measuring from the earliest possible point in boot which inturn implies TPM must be initialised and ready to use before IMA.
To enable integration of tpm_event_log with the IMA subsystem, the TPM drivers (tpm_crb and tpm_crb_ffa) also needs to be built-in. However with FF-A driver also being initialised at device initcall level, it can lead to an initialization order issue where: - crb_acpi_driver_init() may run before tpm_crb_ffa_driver()_init and ffa_init() - As a result, probing the TPM device via CRB over FFA is deferred - ima_init() (called as a late initcall) runs before deferred probe completes, IMA fails to find the TPM and logs the below error:
| ima: No TPM chip found, activating TPM-bypass!
Eventually it fails to generate boot_aggregate with PCR values.
Because of the above stated dependency, the ffa driver needs to initialised before tpm_crb_ffa module to ensure IMA finds the TPM successfully when present.
[ jarkko: reformatted some of the paragraphs because they were going past the 75 character boundary. ]
Signed-off-by: Yeoreum Yun yeoreum.yun@arm.com Reviewed-by: Mimi Zohar zohar@linux.ibm.com Reviewed-by: Sudeep Holla sudeep.holla@arm.com Reviewed-by: Jarkko Sakkinen jarkko@kernel.org Signed-off-by: Jarkko Sakkinen jarkko@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
**Backport Status: YES**
This commit should be backported to stable kernel trees for the following reasons:
1. **Fixes a real bug affecting users**: The commit fixes a boot initialization order issue where IMA (Integrity Measurement Architecture) fails to find the TPM device when using TPM over FF-A (Firmware Framework for Arm Architecture). Without this fix, systems with TPM accessed via FF-A get the error "ima: No TPM chip found, activating TPM-bypass!" and fail to generate boot_aggregate with PCR values, breaking secure boot attestation.
2. **Small and contained change**: The code change is minimal - just changing `module_init(ffa_init)` to `rootfs_initcall(ffa_init)`. This is a one-line change that only affects initialization timing.
3. **No architectural changes**: This is purely an initialization order fix that doesn't introduce new features or change the architecture of the FF-A driver.
4. **Security-critical fix**: IMA is a security subsystem used for secure boot, file integrity, and remote attestation. The bug prevents proper boot measurements from being recorded in the TPM, which is a critical security failure for systems relying on measured boot.
5. **Clear problem and solution**: The commit message clearly explains the initialization order dependency between FF-A, TPM drivers (tpm_crb_ffa), and IMA. The fix ensures FF-A initializes earlier (at rootfs_initcall level) so the TPM is available when IMA initializes (at late_initcall level).
7. **Multiple reviewers**: The patch has been reviewed by relevant maintainers including Mimi Zohar (IMA maintainer), Sudeep Holla (FF-A maintainer), and Jarkko Sakkinen (TPM maintainer).
The change meets all stable kernel criteria: it fixes an important bug, has minimal risk of regression, and is confined to fixing the specific initialization order issue without side effects.
drivers/firmware/arm_ffa/driver.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c index 37eb2e6c2f9f..65bf1685350a 100644 --- a/drivers/firmware/arm_ffa/driver.c +++ b/drivers/firmware/arm_ffa/driver.c @@ -2059,7 +2059,7 @@ static int __init ffa_init(void) kfree(drv_info); return ret; } -module_init(ffa_init); +rootfs_initcall(ffa_init);
static void __exit ffa_exit(void) {