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# qualcomm_avb_exploit_poc

PoC for a Qualcomm ABL bootloader unlock via Keymaster TA unauthenticated `READ/WRITE_KM_DEVICE_STATE`.

Tested on Redmi 14R (flame, Snapdragon 4 Gen 2). Expected to affect other Qualcomm devices with vulnerable ABL builds.

> [!CAUTION]
> **Disclaimer**: This PoC is for **educational and technical research purposes only**. Modifying the RPMB device state or partition table carries a high risk of **permanently bricking** your device. **The author** shall not be held responsible for any damage, data loss, or legal consequences resulting from the use of this PoC. **Proceed at your own risk**.

## Background

`Is_VERIFIED_BOOT_2()` in `QcommModulePkg/Library/avb/VerifiedBoot.c` determined the verified boot path at **runtime** by checking whether a `vbmeta_a` or `vbmeta` partition exists in the GPT. If neither partition is found, the function returns `FALSE`, and the bootloader takes the `NO_AVB` path.

The `NO_AVB` path does not call `KEYMASTER_MILESTONE_CALL`. Once the milestone is set (in the normal AVB2 path), the Keymaster TA refuses to execute `READ_KM_DEVICE_STATE` and `WRITE_KM_DEVICE_STATE`.  Without the milestone, these commands execute without restriction.

## Vulnerability

By renaming the `vbmeta` partition to any other name (e.g. `xbmeta`), `Is_VERIFIED_BOOT_2()` finds no vbmeta partition and returns `FALSE`. This forces the `NO_AVB` path, the milestone is never set, and the Keymaster TA does not block device state operations.

An attacker can then load the Keymaster TA, read the `DeviceInfo` structure from RPMB, set `is_unlocked` and `is_unlock_critical` to `1`, and write it back — effectively unlocking the bootloader without going through `fastboot oem unlock`.

```

vbmeta renamed → Is_VERIFIED_BOOT_2() returns FALSE

→ NO_AVB → KEYMASTER_MILESTONE_CALL skipped

→ Keymaster TA READ/WRITE_KM_DEVICE_STATE not blocked

→ DeviceInfo in RPMB writable → bootloader unlocked

```

## Fix

[edk2: Set VB2 status at compile time](https://git.codelinaro.org/clo/la/abl/tianocore/edk2/-/commit/1b2e5f9c4e95db4c74570b828d047e45f9f426d1)

`Is_VERIFIED_BOOT_2()` now returns a compile-time constant based on the `VERIFIED_BOOT_ENABLED` macro, making the result immune to GPT partition table modifications.

## Prerequisites

1. Write access to partition table and partitions (e.g. via EDL or existing exploit)

2. Rename `vbmeta` partition to anything else (e.g. `xbmeta`) via `sgdisk` or similar

3. Flash and Boot to TWRP

4. Start `qseecomd` daemon

## Usage

```sh

# Read current DeviceInfo state

./poc

# Write unlock flags (triggers confirmation prompt)

./poc -w

```

After successful write, reboot to fastboot and run:

```sh

fastboot -w

```

## Build

```sh

$NDK/toolchains/llvm/prebuilt/linux-x86_64/bin/aarch64-linux-android28-clang -fPIE -pie poc.c -ldl -o poc 

```

## Notes

- `TA_IMG_LEN` is hardcoded to the keymaster partition size (512 KB). Adjust if your device differs.
- This PoC uses `_Static_assert` to ensure the structure size is `0xCA8`. However, even if the size matches, field offsets can vary between SoC models or Android versions.