On 10/5/24 12:43 AM, Steven Price wrote:
From: Sami Mujawar <sami.mujawar@xxxxxxx>
Introduce an arm-cca-guest driver that registers with
the configfs-tsm module to provide user interfaces for
retrieving an attestation token.
When a new report is requested the arm-cca-guest driver
invokes the appropriate RSI interfaces to query an
attestation token.
The steps to retrieve an attestation token are as follows:
1. Mount the configfs filesystem if not already mounted
mount -t configfs none /sys/kernel/config
2. Generate an attestation token
report=/sys/kernel/config/tsm/report/report0
mkdir $report
dd if=/dev/urandom bs=64 count=1 > $report/inblob
hexdump -C $report/outblob
rmdir $report
Signed-off-by: Sami Mujawar <sami.mujawar@xxxxxxx>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Signed-off-by: Steven Price <steven.price@xxxxxxx>
---
v3: Minor improvements to comments and adapt to the renaming of
GRANULE_SIZE to RSI_GRANULE_SIZE.
---
drivers/virt/coco/Kconfig | 2 +
drivers/virt/coco/Makefile | 1 +
drivers/virt/coco/arm-cca-guest/Kconfig | 11 +
drivers/virt/coco/arm-cca-guest/Makefile | 2 +
.../virt/coco/arm-cca-guest/arm-cca-guest.c | 211 ++++++++++++++++++
5 files changed, 227 insertions(+)
create mode 100644 drivers/virt/coco/arm-cca-guest/Kconfig
create mode 100644 drivers/virt/coco/arm-cca-guest/Makefile
create mode 100644 drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
diff --git a/drivers/virt/coco/Kconfig b/drivers/virt/coco/Kconfig
index d9ff676bf48d..ff869d883d95 100644
--- a/drivers/virt/coco/Kconfig
+++ b/drivers/virt/coco/Kconfig
@@ -14,3 +14,5 @@ source "drivers/virt/coco/pkvm-guest/Kconfig"
source "drivers/virt/coco/sev-guest/Kconfig"
source "drivers/virt/coco/tdx-guest/Kconfig"
+
+source "drivers/virt/coco/arm-cca-guest/Kconfig"
diff --git a/drivers/virt/coco/Makefile b/drivers/virt/coco/Makefile
index b69c30c1c720..c3d07cfc087e 100644
--- a/drivers/virt/coco/Makefile
+++ b/drivers/virt/coco/Makefile
@@ -7,3 +7,4 @@ obj-$(CONFIG_EFI_SECRET) += efi_secret/
obj-$(CONFIG_ARM_PKVM_GUEST) += pkvm-guest/
obj-$(CONFIG_SEV_GUEST) += sev-guest/
obj-$(CONFIG_INTEL_TDX_GUEST) += tdx-guest/
+obj-$(CONFIG_ARM_CCA_GUEST) += arm-cca-guest/
diff --git a/drivers/virt/coco/arm-cca-guest/Kconfig b/drivers/virt/coco/arm-cca-guest/Kconfig
new file mode 100644
index 000000000000..9dd27c3ee215
--- /dev/null
+++ b/drivers/virt/coco/arm-cca-guest/Kconfig
@@ -0,0 +1,11 @@
+config ARM_CCA_GUEST
+ tristate "Arm CCA Guest driver"
+ depends on ARM64
+ default m
+ select TSM_REPORTS
+ help
+ The driver provides userspace interface to request and
+ attestation report from the Realm Management Monitor(RMM).
+
+ If you choose 'M' here, this module will be called
+ arm-cca-guest.
diff --git a/drivers/virt/coco/arm-cca-guest/Makefile b/drivers/virt/coco/arm-cca-guest/Makefile
new file mode 100644
index 000000000000..69eeba08e98a
--- /dev/null
+++ b/drivers/virt/coco/arm-cca-guest/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_ARM_CCA_GUEST) += arm-cca-guest.o
diff --git a/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
new file mode 100644
index 000000000000..e22a565cb425
--- /dev/null
+++ b/drivers/virt/coco/arm-cca-guest/arm-cca-guest.c
@@ -0,0 +1,211 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2023 ARM Ltd.
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/cc_platform.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/smp.h>
+#include <linux/tsm.h>
+#include <linux/types.h>
+
+#include <asm/rsi.h>
+
+/**
+ * struct arm_cca_token_info - a descriptor for the token buffer.
+ * @granule: PA of the page to which the token will be written
^^^^^^^^
s/the page/the granule. They are same thing when we have 4KB page size,
but there are conceptually different if I'm correct.
+ * @offset: Offset within granule to start of buffer in bytes
+ * @len: Number of bytes of token data that was retrieved
+ * @result: result of rsi_attestation_token_continue operation
+ */
+struct arm_cca_token_info {
+ phys_addr_t granule;
+ unsigned long offset;
+ int result;
+};
+
+/**
+ * arm_cca_attestation_continue - Retrieve the attestation token data.
+ *
+ * @param: pointer to the arm_cca_token_info
+ *
+ * Attestation token generation is a long running operation and therefore
+ * the token data may not be retrieved in a single call. Moreover, the
+ * token retrieval operation must be requested on the same CPU on which the
+ * attestation token generation was initialised.
+ * This helper function is therefore scheduled on the same CPU multiple
+ * times until the entire token data is retrieved.
+ */
+static void arm_cca_attestation_continue(void *param)
+{
+ unsigned long len;
+ unsigned long size;
+ struct arm_cca_token_info *info;
+
+ if (!param)
+ return;
This check seems unnecessary and can be dropped.
+
+ info = (struct arm_cca_token_info *)param;
+
+ size = RSI_GRANULE_SIZE - info->offset;
+ info->result = rsi_attestation_token_continue(info->granule,
+ info->offset, size, &len);
+ info->offset += len;
+}
+
As I suggested in another reply, the return value type of rsi_attestation_token_continue()
needs to be 'unsigned long'. In that case, the type of struct arm_cca_token_info::result
needs to be adjusted either.
+/**
+ * arm_cca_report_new - Generate a new attestation token.
+ *
+ * @report: pointer to the TSM report context information.
+ * @data: pointer to the context specific data for this module.
+ *
+ * Initialise the attestation token generation using the challenge data
+ * passed in the TSM descriptor. Allocate memory for the attestation token
+ * and schedule calls to retrieve the attestation token on the same CPU
+ * on which the attestation token generation was initialised.
+ *
+ * The challenge data must be at least 32 bytes and no more than 64 bytes. If
+ * less than 64 bytes are provided it will be zero padded to 64 bytes.
+ *
+ * Return:
+ * * %0 - Attestation token generated successfully.
+ * * %-EINVAL - A parameter was not valid.
+ * * %-ENOMEM - Out of memory.
+ * * %-EFAULT - Failed to get IPA for memory page(s).
+ * * A negative status code as returned by smp_call_function_single().
+ */
+static int arm_cca_report_new(struct tsm_report *report, void *data)
+{
+ int ret;
+ int cpu;
+ long max_size;
+ unsigned long token_size;
+ struct arm_cca_token_info info;
+ void *buf;
+ u8 *token __free(kvfree) = NULL;
+ struct tsm_desc *desc = &report->desc;
+
+ if (!report)
+ return -EINVAL;
+
This check seems unnecessary and can be dropped.
+ if (desc->inblob_len < 32 || desc->inblob_len > 64)
+ return -EINVAL;
+
+ /*
+ * Get a CPU on which the attestation token generation will be
+ * scheduled and initialise the attestation token generation.
+ */
+ cpu = get_cpu();
+ max_size = rsi_attestation_token_init(desc->inblob, desc->inblob_len);
+ put_cpu();
+
It seems that put_cpu() is called early, meaning the CPU can go away before
the subsequent call to arm_cca_attestation_continue() ?
+ if (max_size <= 0)
+ return -EINVAL;
+
+ /* Allocate outblob */
+ token = kvzalloc(max_size, GFP_KERNEL);
+ if (!token)
+ return -ENOMEM;
+
+ /*
+ * Since the outblob may not be physically contiguous, use a page
+ * to bounce the buffer from RMM.
+ */
+ buf = alloc_pages_exact(RSI_GRANULE_SIZE, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ /* Get the PA of the memory page(s) that were allocated. */
+ info.granule = (unsigned long)virt_to_phys(buf);
+
+ token_size = 0;
This initial assignment can be moved to where the variable is declared.
+ /* Loop until the token is ready or there is an error. */
^^
Maybe it's the personal preference, I personally prefer to avoid the ending
character '.' for the single line of comment.
+ do {
+ /* Retrieve one RSI_GRANULE_SIZE data per loop iteration. */
+ info.offset = 0;
+ do {
+ /*
+ * Schedule a call to retrieve a sub-granule chunk
+ * of data per loop iteration.
+ */
+ ret = smp_call_function_single(cpu,
+ arm_cca_attestation_continue,
+ (void *)&info, true);
+ if (ret != 0) {
+ token_size = 0;
+ goto exit_free_granule_page;
+ }
+
+ ret = info.result;
+ } while ((ret == RSI_INCOMPLETE) &&
+ (info.offset < RSI_GRANULE_SIZE));
It may be clearer to use 'info.result' here. Besides, unnecessary () exists
in the check.
} while (info.result == RSI_INCOMPLETE &&
info.offset < RSI_GRANULE_SIZE);
Apart from that, we needn't to copy the token over when info.result isn't
RSI_SUCCESS nor RSI_INCOMPLETE.
+
+ /*
+ * Copy the retrieved token data from the granule
+ * to the token buffer, ensuring that the RMM doesn't
+ * overflow the buffer.
+ */
+ if (WARN_ON(token_size + info.offset > max_size))
+ break;
+ memcpy(&token[token_size], buf, info.offset);
+ token_size += info.offset;
+ } while (ret == RSI_INCOMPLETE);
+
As above, it may be clearer to use 'info.result' in the check.
} while (info.result == RSI_INCOMPLETE);
+ if (ret != RSI_SUCCESS) {
+ ret = -ENXIO;
+ token_size = 0;
+ goto exit_free_granule_page;
+ }
+
+ report->outblob = no_free_ptr(token);
+exit_free_granule_page:
+ report->outblob_len = token_size;
+ free_pages_exact(buf, RSI_GRANULE_SIZE);
+ return ret;
+}
+
+static const struct tsm_ops arm_cca_tsm_ops = {
+ .name = KBUILD_MODNAME,
+ .report_new = arm_cca_report_new,
+};
+
+/**
+ * arm_cca_guest_init - Register with the Trusted Security Module (TSM)
+ * interface.
+ *
+ * Return:
+ * * %0 - Registered successfully with the TSM interface.
+ * * %-ENODEV - The execution context is not an Arm Realm.
+ * * %-EINVAL - A parameter was not valid.
+ * * %-EBUSY - Already registered.
+ */
+static int __init arm_cca_guest_init(void)
+{
+ int ret;
+
+ if (!is_realm_world())
+ return -ENODEV;
+
+ ret = tsm_register(&arm_cca_tsm_ops, NULL);
+ if (ret < 0)
+ pr_err("Failed to register with TSM.\n");
+
+ return ret;
+}
+module_init(arm_cca_guest_init);
+
It's probably a bit helpful to print the errno returned from tsm_register().
pr_err("Error %d registering with TSM\n", ret);
The only errno that can be returned from tsm_register() is -EBUSY. So there
is no way for arm_cca_guest_init() to return -EINVAL. The comments need
correction by dropping the description relevant to -EINVAL.
+/**
+ * arm_cca_guest_exit - unregister with the Trusted Security Module (TSM)
+ * interface.
+ */
+static void __exit arm_cca_guest_exit(void)
+{
+ tsm_unregister(&arm_cca_tsm_ops);
+}
+module_exit(arm_cca_guest_exit);
+
+MODULE_AUTHOR("Sami Mujawar <sami.mujawar@xxxxxxx>");
+MODULE_DESCRIPTION("Arm CCA Guest TSM Driver.");
+MODULE_LICENSE("GPL");
The ending character '.' for the module's description may not be needed and can be
dropped.
Thanks,
Gavin
