133 lines
3.9 KiB
Plaintext
133 lines
3.9 KiB
Plaintext
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Introduction:
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=============
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The tz_log driver is a platform device driver that exposes a debugfs
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interface for accessing and displaying diagnostic information related
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to secure code (Trustzone).
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The Secure code (Trustzone) will store the diagnostic data in 4KB of
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IMEM. The address of this IMEM region varies from platform. The
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diagnostic data encodes information related to secure code boot-up,
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reset, interrupt and other attributes in a specific format as shown
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below:
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----------------------------
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| General info |
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| (Magic #, CPU cnt etc) |
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----------------------------
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| VMID info |
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----------------------------
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| Boot info (per CPU) |
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----------------------------
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| Reset info (per CPU) |
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----------------------------
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| Interrupt info (per CPU) |
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----------------------------
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| Data logged by TZ |
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----------------------------
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During the initialization of the driver module, this 4KB of IMEM
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is remapped for access by kernel. Further more, an additonal 4KB
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memory is allocated for storing the formatted data that will be
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displayed by the debugfs interface.
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Once the device is booted up and HLOS is up, the standard debugfs
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interface is used to read out and display this information that
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was logged in by secure code in a specific format as shown below.
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Debugfs is typically mounted with a command like:
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mount -t debugfs none /sys/kernel/debug
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(Or an equivalent /etc/fstab line).
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Note that the debugfs API is exported GPL-only to modules.
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Software description
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====================
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The tz_log module is a Linux platform device driver with a debugfs
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interface. The goal of this module is to provide a way to peek into
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the Trustzone diagnostic information to help debug issues with
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Trustzone. Although, this tz_log platform device driver will be
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compiled into the kernel, the debugfs entries will not be exposed
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unless Trustzone is supported by the platform.
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On loading the tz_log driver, tzdbgfs_init() is invoked. tzdbgfs_init()
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initializes the tz_log debugfs interface. The following is done in
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this initialization call.
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(1) Create a directory "tzdbg", to hold a set of debugfs files
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(2) Create the following debugfs files in the "tzdbg" directory
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- boot_info
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Contains information on the warm boot jump address
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- reset_info
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Contains information on the cause of a CPU reset, number of
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resets occurred on a specific CPU
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- interrupt_info
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Contains information on the number of IRQ and FIQ Interrupts
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(with a brief description), interrupts fired and the number
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of times it is fired on a specific CPU.
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- general_info
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Contains information on number of CPUs supported, magic number,
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version number.
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- vmid_info
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Contains information on VMID supported, with a brief description
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- log
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Debug information (ASCII text) that is logged by Trustzone
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Following are the set of file operation defines and register
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- read()
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- open()
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(3) Remap the IMEM region where the secure code diagnostic information
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is stored.
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(4) Allocate 4KB buffer for storing the formatted information
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to be displayed
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When the tz_log driver is unloaded the tz_log debugfs entries are
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explicitly removed.
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Power Management
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================
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n/a
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Security
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========
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None
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Interface
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=========
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This module will create debugfs files under sys/kernel/debug which
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contains information that can be displayed by using the "cat" command.
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Dependencies
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============
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This driver interacts with Trustzone operating environment, thus depends
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on the TZBSP supported architecture. It also depends on debugfs.
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To do
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=====
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TBD
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