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Sat, 14 Nov 2026 11:34:41 -0800 (PST) Received: from sid-dev-env.cgrhrlrrq2nuffriizdlnb1x4b.xx.internal.cloudapp.net ([4.155.54.158]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b1b24938bdsm5093969a91.1.2026.11.14.11.34.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Nov 2026 11:34:40 -0800 (PST) From: Siddharth Chintamaneni To: Peter Huewe , Jarkko Sakkinen Cc: Jason Gunthorpe , Sudeep Holla , Yeoreum Yun , Stuart Yoder , apais@microsoft.com, rlmenge@gmail.com, hargar@linux.microsoft.com, linux-integrity@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Siddharth Chintamaneni Subject: [PATCH v2 2/4] tpm: tpm_crb_ffa: Only probe when ACPI TPM2 uses FF-A Date: Sat, 14 Nov 2026 19:34:32 +0000 Message-ID: <20261114193434.117714-3-sidchintamaneni@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261114193434.117714-1-sidchintamaneni@gmail.com> References: <20261114193434.117714-1-sidchintamaneni@gmail.com> X-Mailing-List: linux-integrity@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Prior to commit 677042afb97a ("tpm: tpm_crb_ffa: revert defered_probed when tpm_crb_ffa is built-in"), built-in tpm_crb_ffa only registered tpm_crb_ffa_driver from tpm_crb_ffa_init() after crb_acpi_probe() confirmed start_method == ACPI_TPM2_CRB_WITH_ARM_FFA. After that commit, tpm_crb_ffa unconditionally registers on the FF-A bus at device_initcall time (and when loaded as a module) without checking the platform's ACPI TPM2 start method. A platform's firmware may expose a TPM CRB over FF-A Secure Partition for UEFI boot services while advertising a non-FF-A start method to the OS in the ACPI TPM2 table. When the ACPI TPM2 table designates a non-FF-A start method, Linux has no consumer for tpm_crb_ffa and should not probe the FF-A TPM service. On Microsoft Cobalt 200 systems, the ACPI TPM2 table does not use ACPI_TPM2_CRB_WITH_ARM_FFA, yet ffa_init() discovers the FF-A TPM partition and tpm_crb_ffa_probe() unconditionally sends CRB_FFA_GET_INTERFACE_VERSION via FFA_MSG_SEND_DIRECT_REQ2/REQ SMC. That request wedges the calling CPU in Secure World (with Non-Secure interrupts and GICv3 pseudo-NMIs masked), hanging boot with an RCU CPU stall: [ 5.507519] ARM FF-A: Driver version 1.2 [ 5.507519] ARM FF-A: Firmware version 1.2 found [ 5.507551] ARM FF-A: Notification setup failed -61, not enabled [ 7.150580] Freeing initrd memory: 293640K [ 65.515248] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: [ 65.521346] rcu: 10-...0: (3 GPs behind) idle=dd9c/1/0x4000000000000000 softirq=37/37 fqs=5262 [ 65.530031] rcu: hardirqs softirqs csw/system [ 65.535589] rcu: number: 0 0 0 [ 65.541146] rcu: cputime: 0 0 0 ==> 30028(ms) [ 65.548102] rcu: (detected by 66, t=15010 jiffies, g=-951, q=1384 ncpus=132) [ 65.555228] Sending NMI from CPU 66 to CPUs 10: [ 75.560686] After 10 seconds, these CPUS still haven't responded to the NMI: 10 Check tpm2_acpi_start_method in tpm_crb_ffa_probe() and return -ENODEV unless it equals ACPI_TPM2_CRB_WITH_ARM_FFA. Checking in probe() rather than module_init allows tpm_crb_ffa.ko to load as a symbol dependency of tpm_crb.ko on non-FF-A platforms when built as modules, while skipping FF-A TPM requests unless ACPI advertises the FF-A start method. Fixes: eb93f0734ef1 ("tpm_crb: ffa_tpm: Implement driver compliant to CRB over FF-A") Signed-off-by: Siddharth Chintamaneni --- drivers/char/tpm/tpm_crb_ffa.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/char/tpm/tpm_crb_ffa.c b/drivers/char/tpm/tpm_crb_ffa.c index 025c4d4b17ca..da676da6f3f0 100644 --- a/drivers/char/tpm/tpm_crb_ffa.c +++ b/drivers/char/tpm/tpm_crb_ffa.c @@ -9,9 +9,11 @@ #define pr_fmt(fmt) "CRB_FFA: " fmt +#include #include #include #include +#include "tpm.h" #include "tpm_crb_ffa.h" static unsigned int busy_timeout_ms = 2000; @@ -324,6 +326,9 @@ static int tpm_crb_ffa_probe(struct ffa_device *ffa_dev) struct tpm_crb_ffa *p; int rc; + if (tpm2_acpi_start_method != ACPI_TPM2_CRB_WITH_ARM_FFA) + return -ENODEV; + /* only one instance of a TPM partition is supported */ if (tpm_crb_ffa && !IS_ERR_VALUE(tpm_crb_ffa)) return -EEXIST; -- 2.45.4