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samimujawarctmarinas
samimujawar
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virt: arm-cca-guest: TSM_REPORT support for realms
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@arm.com> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Signed-off-by: Steven Price <steven.price@arm.com> Reviewed-by: Gavin Shan <gshan@redhat.com> Link: https://lore.kernel.org/r/20241017131434.40935-11-steven.price@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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‎drivers/virt/coco/Kconfig

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@@ -14,3 +14,5 @@ source "drivers/virt/coco/pkvm-guest/Kconfig"
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source "drivers/virt/coco/sev-guest/Kconfig"
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source "drivers/virt/coco/tdx-guest/Kconfig"
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source "drivers/virt/coco/arm-cca-guest/Kconfig"

‎drivers/virt/coco/Makefile

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@@ -7,3 +7,4 @@ obj-$(CONFIG_EFI_SECRET) += efi_secret/
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obj-$(CONFIG_ARM_PKVM_GUEST) += pkvm-guest/
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obj-$(CONFIG_SEV_GUEST) += sev-guest/
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obj-$(CONFIG_INTEL_TDX_GUEST) += tdx-guest/
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obj-$(CONFIG_ARM_CCA_GUEST) += arm-cca-guest/

‎drivers/virt/coco/arm-cca-guest/Kconfig

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config ARM_CCA_GUEST
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tristate "Arm CCA Guest driver"
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depends on ARM64
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default m
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select TSM_REPORTS
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help
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The driver provides userspace interface to request and
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attestation report from the Realm Management Monitor(RMM).
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If you choose 'M' here, this module will be called
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arm-cca-guest.

‎drivers/virt/coco/arm-cca-guest/Makefile

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# SPDX-License-Identifier: GPL-2.0-only
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obj-$(CONFIG_ARM_CCA_GUEST) += arm-cca-guest.o

‎drivers/virt/coco/arm-cca-guest/arm-cca-guest.c

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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2023 ARM Ltd.
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*/
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#include <linux/arm-smccc.h>
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#include <linux/cc_platform.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/smp.h>
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#include <linux/tsm.h>
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#include <linux/types.h>
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#include <asm/rsi.h>
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/**
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* struct arm_cca_token_info - a descriptor for the token buffer.
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* @challenge: Pointer to the challenge data
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* @challenge_size: Size of the challenge data
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* @granule: PA of the granule to which the token will be written
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* @offset: Offset within granule to start of buffer in bytes
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* @result: result of rsi_attestation_token_continue operation
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*/
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struct arm_cca_token_info {
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void *challenge;
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unsigned long challenge_size;
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phys_addr_t granule;
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unsigned long offset;
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unsigned long result;
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};
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static void arm_cca_attestation_init(void *param)
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{
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struct arm_cca_token_info *info;
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info = (struct arm_cca_token_info *)param;
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info->result = rsi_attestation_token_init(info->challenge,
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info->challenge_size);
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}
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/**
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* arm_cca_attestation_continue - Retrieve the attestation token data.
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*
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* @param: pointer to the arm_cca_token_info
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*
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* Attestation token generation is a long running operation and therefore
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* the token data may not be retrieved in a single call. Moreover, the
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* token retrieval operation must be requested on the same CPU on which the
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* attestation token generation was initialised.
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* This helper function is therefore scheduled on the same CPU multiple
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* times until the entire token data is retrieved.
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*/
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static void arm_cca_attestation_continue(void *param)
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{
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unsigned long len;
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unsigned long size;
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struct arm_cca_token_info *info;
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info = (struct arm_cca_token_info *)param;
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size = RSI_GRANULE_SIZE - info->offset;
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info->result = rsi_attestation_token_continue(info->granule,
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info->offset, size, &len);
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info->offset += len;
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}
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/**
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* arm_cca_report_new - Generate a new attestation token.
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*
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* @report: pointer to the TSM report context information.
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* @data: pointer to the context specific data for this module.
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*
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* Initialise the attestation token generation using the challenge data
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* passed in the TSM descriptor. Allocate memory for the attestation token
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* and schedule calls to retrieve the attestation token on the same CPU
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* on which the attestation token generation was initialised.
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*
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* The challenge data must be at least 32 bytes and no more than 64 bytes. If
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* less than 64 bytes are provided it will be zero padded to 64 bytes.
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*
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* Return:
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* * %0 - Attestation token generated successfully.
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* * %-EINVAL - A parameter was not valid.
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* * %-ENOMEM - Out of memory.
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* * %-EFAULT - Failed to get IPA for memory page(s).
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* * A negative status code as returned by smp_call_function_single().
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*/
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static int arm_cca_report_new(struct tsm_report *report, void *data)
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{
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int ret;
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int cpu;
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long max_size;
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unsigned long token_size = 0;
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struct arm_cca_token_info info;
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void *buf;
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u8 *token __free(kvfree) = NULL;
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struct tsm_desc *desc = &report->desc;
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if (desc->inblob_len < 32 || desc->inblob_len > 64)
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return -EINVAL;
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/*
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* The attestation token 'init' and 'continue' calls must be
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* performed on the same CPU. smp_call_function_single() is used
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* instead of simply calling get_cpu() because of the need to
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* allocate outblob based on the returned value from the 'init'
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* call and that cannot be done in an atomic context.
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*/
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cpu = smp_processor_id();
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info.challenge = desc->inblob;
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info.challenge_size = desc->inblob_len;
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ret = smp_call_function_single(cpu, arm_cca_attestation_init,
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&info, true);
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if (ret)
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return ret;
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max_size = info.result;
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if (max_size <= 0)
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return -EINVAL;
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/* Allocate outblob */
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token = kvzalloc(max_size, GFP_KERNEL);
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if (!token)
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return -ENOMEM;
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/*
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* Since the outblob may not be physically contiguous, use a page
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* to bounce the buffer from RMM.
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*/
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buf = alloc_pages_exact(RSI_GRANULE_SIZE, GFP_KERNEL);
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if (!buf)
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return -ENOMEM;
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/* Get the PA of the memory page(s) that were allocated */
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info.granule = (unsigned long)virt_to_phys(buf);
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/* Loop until the token is ready or there is an error */
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do {
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/* Retrieve one RSI_GRANULE_SIZE data per loop iteration */
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info.offset = 0;
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do {
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/*
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* Schedule a call to retrieve a sub-granule chunk
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* of data per loop iteration.
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*/
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ret = smp_call_function_single(cpu,
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arm_cca_attestation_continue,
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(void *)&info, true);
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if (ret != 0) {
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token_size = 0;
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goto exit_free_granule_page;
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}
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} while (info.result == RSI_INCOMPLETE &&
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info.offset < RSI_GRANULE_SIZE);
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if (info.result != RSI_SUCCESS) {
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ret = -ENXIO;
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token_size = 0;
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goto exit_free_granule_page;
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}
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/*
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* Copy the retrieved token data from the granule
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* to the token buffer, ensuring that the RMM doesn't
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* overflow the buffer.
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*/
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if (WARN_ON(token_size + info.offset > max_size))
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break;
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memcpy(&token[token_size], buf, info.offset);
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token_size += info.offset;
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} while (info.result == RSI_INCOMPLETE);
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report->outblob = no_free_ptr(token);
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exit_free_granule_page:
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report->outblob_len = token_size;
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free_pages_exact(buf, RSI_GRANULE_SIZE);
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return ret;
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}
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static const struct tsm_ops arm_cca_tsm_ops = {
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.name = KBUILD_MODNAME,
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.report_new = arm_cca_report_new,
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};
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/**
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* arm_cca_guest_init - Register with the Trusted Security Module (TSM)
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* interface.
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*
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* Return:
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* * %0 - Registered successfully with the TSM interface.
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* * %-ENODEV - The execution context is not an Arm Realm.
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* * %-EBUSY - Already registered.
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*/
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static int __init arm_cca_guest_init(void)
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{
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int ret;
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if (!is_realm_world())
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return -ENODEV;
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ret = tsm_register(&arm_cca_tsm_ops, NULL);
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if (ret < 0)
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pr_err("Error %d registering with TSM\n", ret);
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return ret;
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}
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module_init(arm_cca_guest_init);
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/**
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* arm_cca_guest_exit - unregister with the Trusted Security Module (TSM)
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* interface.
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*/
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static void __exit arm_cca_guest_exit(void)
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{
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tsm_unregister(&arm_cca_tsm_ops);
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}
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module_exit(arm_cca_guest_exit);
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MODULE_AUTHOR("Sami Mujawar <sami.mujawar@arm.com>");
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MODULE_DESCRIPTION("Arm CCA Guest TSM Driver");
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MODULE_LICENSE("GPL");

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