linux-kernel - [PATCH v2 4/4] firmware: qcom: scm: request the waitqueue irq *after* initializing SCM

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Message-Id: <20250630-qcom-scm-race-v2-4-fa3851c98611@linaro.org>
Date: Mon, 30 Jun 2025 14:12:05 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Bjorn Andersson <andersson@...nel.org>, 
 Konrad Dybcio <konradybcio@...nel.org>, Johan Hovold <johan@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, 
 Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: [PATCH v2 4/4] firmware: qcom: scm: request the waitqueue irq
 *after* initializing SCM

From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

There's a subtle race in the SCM driver: we assign the __scm pointer
before requesting the waitqueue interrupt. Assigning __scm marks the SCM
API as ready to accept calls. It's possible that a user makes a call
right after we set __scm and the firmware raises an interrupt before the
driver's ready to service it. Move the __scm assignment after we request
the interrupt.

This has the added benefit of allowing us to drop the goto label.

Reviewed-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 drivers/firmware/qcom/qcom_scm.c | 36 ++++++++++++++----------------------
 1 file changed, 14 insertions(+), 22 deletions(-)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index b6e0420bb2b72247e4d772b66314d81f336f5d9d..26cd0458aacd67dcd36f065675e969cea97eb465 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -2276,29 +2276,27 @@ static int qcom_scm_probe(struct platform_device *pdev)
 		return dev_err_probe(scm->dev, PTR_ERR(scm->mempool),
 				     "Failed to create the SCM memory pool\n");
 
+	irq = platform_get_irq_optional(pdev, 0);
+	if (irq < 0) {
+		if (irq != -ENXIO)
+			return irq;
+	} else {
+		ret = devm_request_threaded_irq(scm->dev, irq, NULL, qcom_scm_irq_handler,
+						IRQF_ONESHOT, "qcom-scm", scm);
+		if (ret < 0)
+			return dev_err_probe(scm->dev, ret,
+					     "Failed to request qcom-scm irq\n");
+	}
+
 	/*
 	 * Paired with smp_load_acquire() in qcom_scm_is_available().
 	 *
 	 * This marks the SCM API as ready to accept user calls and can only
-	 * be called after the TrustZone memory pool is initialized.
+	 * be called after the TrustZone memory pool is initialized and the
+	 * waitqueue interrupt requested.
 	 */
 	smp_store_release(&__scm, scm);
 
-	irq = platform_get_irq_optional(pdev, 0);
-	if (irq < 0) {
-		if (irq != -ENXIO) {
-			ret = irq;
-			goto err;
-		}
-	} else {
-		ret = devm_request_threaded_irq(__scm->dev, irq, NULL, qcom_scm_irq_handler,
-						IRQF_ONESHOT, "qcom-scm", __scm);
-		if (ret < 0) {
-			dev_err_probe(scm->dev, ret, "Failed to request qcom-scm irq\n");
-			goto err;
-		}
-	}
-
 	__get_convention();
 
 	/*
@@ -2328,12 +2326,6 @@ static int qcom_scm_probe(struct platform_device *pdev)
 	WARN(ret < 0, "failed to initialize qseecom: %d\n", ret);
 
 	return 0;
-
-err:
-	/* Paired with smp_load_acquire() in qcom_scm_is_available(). */
-	smp_store_release(&__scm, NULL);
-
-	return ret;
 }
 
 static void qcom_scm_shutdown(struct platform_device *pdev)

-- 
2.48.1