linux-kernel - [PATCH v2 1/1] arm64: rsi: Add automatic arm-cca-guest module loading

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Message-ID: <20241203000156.72451-2-jeremy.linton@arm.com>
Date: Mon,  2 Dec 2024 18:01:56 -0600
From: Jeremy Linton <jeremy.linton@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: gshan@...hat.com,
	steven.price@....com,
	sami.mujawar@....com,
	suzuki.poulose@....com,
	will@...nel.org,
	catalin.marinas@....com,
	linux-kernel@...r.kernel.org,
	Jeremy Linton <jeremy.linton@....com>
Subject: [PATCH v2 1/1] arm64: rsi: Add automatic arm-cca-guest module loading

The TSM module provides both guest identification as well as
attestation when a guest is run in CCA mode. Lets assure by creating a
dummy platform device that the module is automatically loaded during
boot.  The TSM module will be loaded by udev daemon after it receives
the device addition event. Once it is in place it can be used earlier
in the boot process to say decrypt a LUKS rootfs.

Signed-off-by: Jeremy Linton <jeremy.linton@....com>
---
 arch/arm64/include/asm/rsi.h                    |  2 ++
 arch/arm64/kernel/rsi.c                         | 15 +++++++++++++++
 drivers/virt/coco/arm-cca-guest/arm-cca-guest.c |  8 ++++++++
 3 files changed, 25 insertions(+)

diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
index 188cbb9b23f5..b42aeac05340 100644
--- a/arch/arm64/include/asm/rsi.h
+++ b/arch/arm64/include/asm/rsi.h
@@ -10,6 +10,8 @@
 #include <linux/jump_label.h>
 #include <asm/rsi_cmds.h>
 
+#define RSI_PDEV_NAME "arm-cca-dev"
+
 DECLARE_STATIC_KEY_FALSE(rsi_present);
 
 void __init arm64_rsi_init(void);
diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 3031f25c32ef..5434e5496ac2 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -8,6 +8,7 @@
 #include <linux/psci.h>
 #include <linux/swiotlb.h>
 #include <linux/cc_platform.h>
+#include <linux/platform_device.h>
 
 #include <asm/io.h>
 #include <asm/mem_encrypt.h>
@@ -140,3 +141,17 @@ void __init arm64_rsi_init(void)
 	static_branch_enable(&rsi_present);
 }
 
+static struct platform_device rsi_dev = {
+	.name = RSI_PDEV_NAME,
+	.id = PLATFORM_DEVID_NONE
+};
+
+static int __init rsi_init(void)
+{
+	if (is_realm_world() &&
+	    platform_device_register(&rsi_dev))
+		pr_err("failed to register rsi platform device\n");
+	return 0;
+}
+
+arch_initcall(rsi_init)
diff --git a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
index 488153879ec9..1f8d8439f617 100644
--- a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
+++ b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
@@ -6,6 +6,7 @@
 #include <linux/arm-smccc.h>
 #include <linux/cc_platform.h>
 #include <linux/kernel.h>
+#include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/smp.h>
 #include <linux/tsm.h>
@@ -219,6 +220,13 @@ static void __exit arm_cca_guest_exit(void)
 }
 module_exit(arm_cca_guest_exit);
 
+/* modalias, so userspace can autoload this module when RSI is available */
+static const struct __maybe_unused platform_device_id arm_cca_match[] = {
+	{ RSI_PDEV_NAME, 0},
+	{ }
+};
+
+MODULE_DEVICE_TABLE(platform, arm_cca_match);
 MODULE_AUTHOR("Sami Mujawar <sami.mujawar@....com>");
 MODULE_DESCRIPTION("Arm CCA Guest TSM Driver");
 MODULE_LICENSE("GPL");
-- 
2.46.0