From: Yeoreum Yun yeoreum.yun@arm.com
[ Upstream commit 746d9e9f62a6e8ba0eba2b83fc61cfe7fa8797ce ]
To generate the boot_aggregate log in the IMA subsystem using TPM PCR values, the TPM driver must be built as built-in and must be probed before the IMA subsystem is initialized.
However, when the TPM device operates over the FF-A protocol using the CRB interface, probing fails and returns -EPROBE_DEFER if the tpm_crb_ffa device — an FF-A device that provides the communication interface to the tpm_crb driver — has not yet been probed.
This issue occurs because both crb_acpi_driver_init() and tpm_crb_ffa_driver_init() are registered with device_initcall. As a result, crb_acpi_driver_init() may be invoked before tpm_crb_ffa_driver_init(), which is responsible for probing the tpm_crb_ffa device.
When this happens, IMA fails to detect the TPM device and logs the following message:
| ima: No TPM chip found, activating TPM-bypass!
Consequently, it cannot generate the boot_aggregate log with the PCR values provided by the TPM.
To resolve this issue, the tpm_crb_ffa_init() function explicitly attempts to probe the tpm_crb_ffa by register tpm_crb_ffa driver so that when tpm_crb_ffa device is created before tpm_crb_ffa_init(), probe the tpm_crb_ffa device in tpm_crb_ffa_init() to finish probe the TPM device completely.
This ensures that the TPM device using CRB over FF-A can be successfully probed, even if crb_acpi_driver_init() is called first.
[ 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 functional bug affecting users**: The commit addresses a race condition where IMA (Integrity Measurement Architecture) fails to detect TPM devices that use CRB over FF-A, resulting in the message "ima: No TPM chip found, activating TPM-bypass!" This prevents IMA from generating boot_aggregate logs with TPM PCR values, which is a critical security feature.
2. **Small and contained fix**: The change is minimal and focused: - Adds a static forward declaration of `tpm_crb_ffa_driver` - Modifies `tpm_crb_ffa_init()` to explicitly register the FFA driver when built-in - Adds conditional compilation guards around `module_ffa_driver()`
3. **No architectural changes**: The fix doesn't introduce new features or change the architecture. It simply ensures proper driver registration ordering when the driver is built-in.
4. **Clear root cause**: The issue occurs because both `crb_acpi_driver_init()` and `tpm_crb_ffa_driver_init()` are registered with `device_initcall`, leading to unpredictable initialization order. When `crb_acpi_driver_init()` runs first, it calls `tpm_crb_ffa_init()` which returns `-ENOENT` because the FFA driver hasn't been registered yet.
5. **Security implications**: TPM is a critical security component, and IMA's inability to use TPM measurements compromises system integrity attestation. This fix ensures security features work as intended.
6. **Minimal risk**: The changes only affect the initialization path when `CONFIG_TCG_ARM_CRB_FFA` is built-in (not as a module). The fix: - Only executes when `!IS_MODULE(CONFIG_TCG_ARM_CRB_FFA)` - Preserves existing error handling - Doesn't change the module case behavior
7. **Well-reviewed**: The commit has been reviewed by multiple maintainers including Mimi Zohar (IMA maintainer), Sudeep Holla (ARM FF-A maintainer), and Jarkko Sakkinen (TPM maintainer).
The fix is important for ARM systems using FF-A to communicate with TPM devices, ensuring that security features like IMA work correctly when TPM drivers are built into the kernel.
drivers/char/tpm/tpm_crb_ffa.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c index 4ead61f01299..462fcf610020 100644 --- a/drivers/char/tpm/tpm_crb_ffa.c +++ b/drivers/char/tpm/tpm_crb_ffa.c @@ -115,6 +115,7 @@ struct tpm_crb_ffa { };
static struct tpm_crb_ffa *tpm_crb_ffa; +static struct ffa_driver tpm_crb_ffa_driver;
static int tpm_crb_ffa_to_linux_errno(int errno) { @@ -168,13 +169,23 @@ static int tpm_crb_ffa_to_linux_errno(int errno) */ int tpm_crb_ffa_init(void) { + int ret = 0; + + if (!IS_MODULE(CONFIG_TCG_ARM_CRB_FFA)) { + ret = ffa_register(&tpm_crb_ffa_driver); + if (ret) { + tpm_crb_ffa = ERR_PTR(-ENODEV); + return ret; + } + } + if (!tpm_crb_ffa) - return -ENOENT; + ret = -ENOENT;
if (IS_ERR_VALUE(tpm_crb_ffa)) - return -ENODEV; + ret = -ENODEV;
- return 0; + return ret; } EXPORT_SYMBOL_GPL(tpm_crb_ffa_init);
@@ -369,7 +380,9 @@ static struct ffa_driver tpm_crb_ffa_driver = { .id_table = tpm_crb_ffa_device_id, };
+#ifdef MODULE module_ffa_driver(tpm_crb_ffa_driver); +#endif
MODULE_AUTHOR("Arm"); MODULE_DESCRIPTION("TPM CRB FFA driver");