An issue was discovered in the Arm Mali GPU Kernel Driver. A non-privileged user can make improper GPU processing operations to gain access to already freed memory, write a limited amount outside of buffer bounds, or to disclose details of memory mappings. This affects Midgard r4p0 through r32p0, Bifrost r0p0 through r38p0 and r39p0 before r38p1, and Valhall r19p0 through r38p0 and r39p0 before r38p1.
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Bifrost | Arm | r0p0 (including) | r38p0 (including) |
| Bifrost | Arm | r39p0 (including) | r39p0 (including) |
| Midgard | Arm | r4p0 (including) | r32p0 (including) |
| Valhall | Arm | r19p0 (including) | r38p0 (including) |
| Valhall | Arm | r39p0 (including) | r39p0 (including) |
The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:
In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.