Summary The NPU device’s kernel driver implements a set of ioctl handlers one of which uses unsanitized user data as an index into a function pointer array. The user provided values can exceed the boundaries of the legitimate array and might cause user controlled values to be called as function pointers. A malicious actor can use this vulnerability to hijack the control flow of the kernel and call arbitrary functions with controlled parameters. The function pointer callsite is protected by clang’s CFI, which reduces the number of function that can be called through this primitive. The mmap handler is exposed through the /dev/davinci0 character device.

Summary The NPU device’s kernel driver implements a custom mmap handler that exposes trusted kernel data to user space. These exposed structures contain sensitive data, including kernel pointers, which can be controlled by a user process. The content of these structures is inherently trusted by the kernel, the pointers are accessed for reading and writing at various places. This provides a very convenient arbitrary kernel read-write primitive that can be abused by an attacker to compromise the integrity of the kernel achieve kernel code execution and gain elevated privileges. The mmap handler is exposed through the /dev/davinci0 character device. Due to the applied selinux policy, access to this device is restricted to the hiaiserver system process.

Summary Due to a bug in the way mappings are closed it is possible to free a kmallocated memory chunk arbitrary times. This vulnerability can be used to craft a use after free scenario against any kernel structure that is allocated from the kmalloc-64 cache. There is rich public literature on how such use after free vulnerabilities can be utilized to compromise the kernel, achieve code execution in kernel context, and elevate privileges of user space processes. Even when modern mitigation is deployed. The mmap handler is exposed through the /dev/davinci0 character device. Due to the applied selinux policy, access to this device is restricted to the hiaiserver system process.

Summary The NPU device’s kernel driver implements a set of ioctl handlers one of which uses unsanitized user data as an offset to retrieve a kernel structure. Fields of the structure are written with user provided values. A malicious actor can use this vulnerability to overwrite kernel memory with controlled data. The mmap handler is exposed through the /dev/davinci0 character device. Due to the applied selinux policy, access to this device is restricted to the hiaiserver system process. Because of these limitations a practical attack would need to target the hiaiserver first. The /dev/davinci0 device exposes a series of ioctl handlers, one of which is devdrv_ioctl_load_stream_buff.

Summary In a previous advisory we disclosed multiple vulnerabilities within the NPU device’s mmap handler and discussed how it exposes sensitive kernel data. This advisory focuses on the implementation errors in the same handler. The mapping function ignores the requested size parameter and fails to back regions of the mapped virtual memory with an actual mapping. Trying to access these holes or requesting an mmap that is smaller than the memory mapped by the kernel driver results in a kernel crash, most likely caused by invalid page accesses. The mmap handler is exposed through the /dev/davinci0 character device. Due to the applied selinux policy, access to this device is restricted to the hiaiserver system process.