Introduction to UFS and Physical Extractions

Universal Flash Storage (UFS) has become the prevalent embedded storage standard in modern high-end mobile devices and automotive systems, largely superseding eMMC. UFS offers significant performance advantages due to its SCSI-like command set, full-duplex MIPI M-PHY interface, and command queuing capabilities. These advancements, while beneficial for user experience, introduce new complexities for data forensics and reverse engineering when attempting to reconstruct filesystems from physically extracted raw data.

Physical data extraction, often referred to as a "chip-off" procedure, involves desoldering the UFS memory chip directly from the device’s Printed Circuit Board (PCB). Once removed, specialized forensic tools and hardware programmers are used to read the raw contents of the flash memory. Unlike eMMC, which typically presents as a single logical block device, UFS devices organize their storage into Logical Units (LUNs). A raw UFS dump is essentially a bit-for-bit copy of the underlying physical memory, which includes all LUNs, boot configurations, and potentially unallocated space. The challenge then shifts from obtaining the data to intelligently parsing and reconstructing the various filesystems contained within this monolithic raw dump.

Understanding UFS Logical Units (LUNs)

A core concept in UFS is the Logical Unit (LUN). Unlike eMMC’s single user partition, a UFS device can expose multiple LUNs, each functioning as an independent block device. Common LUNs include:

• LUN 0: Typically the User Data Partition, containing the Android filesystem (e.g., /data).
• LUN 1: Often the System Partition, containing /system.
• LUN 2: Can be the Vendor Partition, containing /vendor.
• LUN 3-7: Potentially other partitions like /cache, /metadata, or OEM-specific partitions.
• Well Known LUNs (WLU): These are special LUNs (e.g., Boot LUNs, RPMB LUN) not directly used for user data but critical for device operation and security. While typically not part of the primary filesystem reconstruction, their presence can affect the size and structure of a raw dump.

The raw dump obtained via chip-off will be a concatenation of these LUNs, sometimes padded or interspersed with other UFS controller metadata. The first step in reconstruction is to identify the boundaries of these individual LUNs and treat them as separate disk images.

Initial Analysis and Partition Table Identification

Once you have a raw UFS dump (e.g., ufs_raw_dump.bin), the initial analysis involves identifying the partition table. Modern Android devices almost exclusively use the GUID Partition Table (GPT) scheme, which is typically found at the beginning of the storage medium (LUN 0, or the first addressable block of the dump). You can use forensic tools or command-line utilities for this.

Using gdisk for GPT Analysis

gdisk (GPT fdisk) is an excellent command-line tool for inspecting and manipulating GPTs. Although designed for block devices, it can operate on disk images.

gdisk -l ufs_raw_dump.bin

This command will attempt to read the GPT from the raw dump and list all detected partitions, their start sectors, and sizes. This output is crucial for understanding the layout of your raw dump.

Manual Inspection with a Hex Editor

If automated tools fail or you need a deeper understanding, a hex editor (like HxD, 010 Editor, or `bless` on Linux) can be used. Look for the GPT header signature (EFI PART) at offset 512 bytes (sector 1) for the primary GPT, and potentially at the end of the dump for the secondary GPT header. Each GPT entry will contain the UUID, starting LBA (Logical Block Address), and ending LBA of a partition.

Extracting Individual LUNs/Partitions

Once you have the start and end sectors (or byte offsets) of each partition from the GPT analysis, you can use the dd command to carve out each LUN or partition into its own separate image file. Assuming a sector size of 512 bytes, the calculation is straightforward:

dd if=ufs_raw_dump.bin of=partition_name.img bs=512 skip=<start_sector> count=<number_of_sectors>

For example, if gdisk reported LUN 0 (Userdata) starting at sector 2048 and being 100,000,000 sectors long:

dd if=ufs_raw_dump.bin of=userdata_lun0.img bs=512 skip=2048 count=100000000 status=progress

Repeat this for all identified partitions (e.g., system, vendor, cache) to get individual filesystem images.

Identifying and Mounting Filesystems

With the individual partition images, the next step is to identify their filesystem types and attempt to mount them. Common Android filesystems include ext4 (for /system, /vendor, /cache) and F2FS (Flash-Friendly File System, often for /data).

Identifying Filesystem Type

The file command is invaluable for this:

file userdata_lun0.img

It might output something like: userdata_lun0.img: Linux rev 1.0 ext4 filesystem data, UUID=... or userdata_lun0.img: Linux f2fs filesystem.

Mounting Filesystems

For `ext4` filesystems:

sudo mkdir /mnt/userdata_ext4sudo mount -o loop userdata_lun0.img /mnt/userdata_ext4

For `f2fs` filesystems, you might need to specify the type explicitly if automatic detection fails:

sudo mkdir /mnt/userdata_f2fssudo mount -t f2fs -o loop userdata_lun0.img /mnt/userdata_f2fs

If the mount is successful, you can now browse the filesystem content within the mounted directory.

Data Carving and Recovery

Sometimes, partitions might be corrupted, or specific files might have been deleted, making a direct mount impossible or incomplete. In such cases, data carving tools can be used on the raw LUN images to recover files based on their headers and footers.

• foremost: A popular open-source tool for carving specific file types.

foremost -t jpg,pdf,zip -i userdata_lun0.img -o /recovery_output/

• scalpel: A more advanced and faster file carving tool, often preferred for larger datasets.

scalpel -o /recovery_output/ -c /etc/scalpel/scalpel.conf userdata_lun0.img

You would configure scalpel.conf to specify the file types you are interested in recovering.

Challenges and Advanced Considerations

Even with a successfully reconstructed filesystem, several factors can impede data access:

• Full Disk Encryption (FDE) / File-Based Encryption (FBE): Most modern Android devices employ encryption. While you can reconstruct the filesystem structure, the actual data within encrypted partitions (especially /data) will remain unintelligible without the encryption keys. Recovering these keys typically requires accessing device secrets (e.g., secure boot keys, password hashes) which are often stored in Trusted Execution Environments (TEE) and are extremely difficult to extract.
• Wear Leveling and ECC: UFS controllers handle wear leveling and Error-Correcting Code (ECC) internally. A raw physical dump typically bypasses these controller functions, meaning you are reading the raw flash cells. If the extraction hardware doesn’t account for NAND-specific ECC, the data might be corrupted. High-quality chip-off tools usually handle this to present a logical view.
• Trim Commands: UFS supports TRIM, which allows the OS to inform the controller that certain data blocks are no longer in use and can be erased. Post-TRIM data is often unrecoverable from the flash.

Decoding UFS raw dumps is a multi-stage process requiring a deep understanding of UFS architecture, partition schemes, and filesystem structures. While challenging, the systematic application of forensic tools and techniques enables expert-level recovery and analysis of critical data from compromised or locked Android devices.