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  Exploring Lenovo T480 NVRAM Variables With CHIPSEC »


CHIPSEC V1.8.1 UEFI SHELL SPI DUMP COMMAND ERROR

CHIPSEC is a “extensible framework for analyzing platform level security of
hardware, devices, system firmware, low-level protection mechanisms, and the
configuration of various platform components. It contains a set of modules,
including simple tests for hardware protections and correct configuration, tests
for vulnerabilities in firmware and platform components, security assessment and
fuzzing tools for various platform devices and interfaces, and tools acquiring
critical firmware and device artifacts”.

CHIPSEC is mostly written in Python for portability and can run on Linux,
Windows, Mac OSX, DAL, and the UEFI shell. It is Intel-centric at this time.

The recent update from Python 2 from Python 3 broke a couple of commands. For
example, in version 1.8.1, I am getting a TypeError: argument 3 must be str, not
bytes exception when I invoke chipsec_util.py spi dump rom.bin from a UEFI
shell.

Here is the full error details:


################################################################
CHIPSEC: Platform Hardware Security Assessment Framework
################################################################
[CHIPSEC] Version : 1.8.0
[CHIPSEC] OS : uefi
[CHIPSEC] Python : 3.6.8 (64-bit)

[CHIPSEC] API mode: using CHIPSEC kernel module API
[CHIPSEC] Helper : EfiHelper (None)
[CHIPSEC] Platform: Mobile 8th Generation Core Processor (Kabylake U-Quad Core)
[CHIPSEC] VID: 8086
[CHIPSEC] DID: 5914
[CHIPSEC] RID: 08
[CHIPSEC] PCH : PCH-U with iHDCP 2.2 Premium
[CHIPSEC] VID: 8086
[CHIPSEC] DID: 9D4E
[CHIPSEC] RID: 21
[CHIPSEC] Executing command 'spi' with args ['dump', 'rom.bin']

[CHIPSEC] Dumping entire SPI flash memory to 'rom.bin'
[CHIPSEC] it may take a few minutes (use DEBUG or VERBOSE logger options to see progress)
[CHIPSEC] BIOS region: base = 0x00700000, limit = 0x00FFFFFF
[CHIPSEC] Dumping 0x01000000 bytes (to the end of BIOS region)
[spi] reading 0x1000000 bytes from SPI at FLA = 0x0 (in 262144 0x40-byte chunks + 0x0-byte remainder)
Traceback (most recent call last):
File "chipsec_util.py", line 218, in
sys.exit( main() )
File "chipsec_util.py", line 214, in main
return chipsecUtil.main()
File "chipsec_util.py", line 189, in main
comm.run()
File "FS1:\chipsec\chipsec\utilcmd\spi_cmd.py", line 182, in run
self.func()
File "FS1:\chipsec\chipsec\utilcmd\spi_cmd.py", line 108, in spi_dump
buf = self._spi.read_spi_to_file( 0, spi_size, self.out_file )
File "FS1:\chipsec\chipsec\hal\spi.py", line 564, in read_spi_to_file
buf = self.read_spi( spi_fla, data_byte_count )
File "FS1:\chipsec\chipsec\hal\spi.py", line 592, in read_spi
cycle_done = self._wait_SPI_flash_cycle_done()
File "FS1:\chipsec\chipsec\hal\spi.py", line 507, in _wait_SPI_flash_cycle_done
self.spi_reg_write( self.hsfs_off, HSFSTS_CLEAR, 1 )
File "FS1:\chipsec\chipsec\hal\spi.py", line 243, in spi_reg_write
return self.mmio.write_MMIO_reg(self.rcba_spi_base, reg, value, size)
File "FS1:\chipsec\chipsec\hal\mmio.py", line 112, in write_MMIO_reg
self.cs.helper.write_mmio_reg( bar_base, size, value, offset, bar_size )
File "FS1:\chipsec\chipsec\helper\oshelper.py", line 192, in write_mmio_reg
ret = self.helper.write_mmio_reg(bar_base +offset, size, value )
File "FS1:\chipsec\chipsec\helper\efi\efihelper.py", line 166, in write_mmio_reg
edk2.writemem(phys_address_lo, phys_address_hi, buf, size)
TypeError: argument 3 must be str, not bytes



The fix was simple. All that was required was to modify one line of code in
write_mmio_reg() which is in …/chipsec/helper/efi/efihelper.py, and also import
bytestostring from chipsec.defines in the same file.

Here is the existing version 1.8.1 code for write_mmio_reg:


1
2
3
4
5
6
7
8
def write_mmio_reg(self, phys_address, size, value):
    phys_address_lo = phys_address & 0xFFFFFFFF
    phys_address_hi = (phys_address >> 32) & 0xFFFFFFFF
    if size == 4:
        return edk2.writemem_dword(phys_address_lo, phys_address_hi, value)
    else:
        buf = struct.pack(size * "B", value)
        edk2.writemem(phys_address_lo, phys_address_hi, buf, size)


Here is the modified code that works:


1
2
3
4
5
6
7
8
def write_mmio_reg(self, phys_address, size, value):
    phys_address_lo = phys_address & 0xFFFFFFFF
    phys_address_hi = (phys_address >> 32) & 0xFFFFFFFF
    if size == 4:
        return edk2.writemem_dword(phys_address_lo, phys_address_hi, value)
    else:
        buf = bytestostring( struct.pack(size * "B", value) )
        edk2.writemem(phys_address_lo, phys_address_hi, buf, size)


What is bytestostring you may ask and why is the change necessary?

Here is the definition of bytestostring from …/chipsec/defines.py:


1
2
3
4
5
def bytestostring(mbytes):
    if isinstance(mbytes, bytes):
        return mbytes.decode("latin_1")
    else:
        return mbytes


Note that the real work is done by the mbytes object’s mbytes.decode method. As
an aside, I am not sure why latin_1 was chosen by the developers of CHIPSEC as
the decoded string format but it works.

For completeness, some notes about Python 3 TypeError follow. As you are
probably aware, Python 3 is a much stricter object-orientated programming
language than Python 2. It always checks the type of object you are passing and
whether a particular object type supports the operation. If there is a mismatch,
Python 3 will throw a TypeError exception error. Note that type constraints are
not checked at compile time; therefore operations on an object may fail at
runtime if the given object is not of a suitable type.

Looking back at the defective source code, you can see that the line
struct.pack(size * “B”, value) returns a bytes object in buf. struct.pack is
part of the struct.py module which performs conversions between Python values
and C structs represented as Python bytes objects. In this case, “B” is the
format character for unsigned char C type (Python – integer type) whose size is
1 byte. However edk2.writemem expects a string for the third argument – not a
bytes object. This mismatch of types causes the TypeError exception.

Enjoy!

February 10th, 2022


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