Exploit Methods/Userspace data usage
Details
Sometimes an attacker won't be able to control the instruction pointer directly, but they will be able to redirect the dereference a structure or other pointer. In these cases, it is easiest to aim at malicious structures that have been built in userspace to perform the exploitation.
Note that this is a superset that includes Userspace execution. If we can protect against userspace access, we'll also be protecting against userspace execution.
Examples
Mitigations
- hardware segmentation: SMAP (x86), PAN (arm, arm64), Domains (arm)
- emulated PAN (memory segmentation via segments, Domains, page table swapping, PCID, etc. e.g. PAX_MEMORY_UDEREF)
Right now, the upstream options available for Privileged Access Never (PAN) are:
| CPU | Feature Name | |
|---|---|---|
| ARM | v7 (32-bit) | CONFIG_CPU_SW_DOMAIN_PAN (since Linux v4.3) |
| v8.0 (64-bit) | CONFIG_ARM64_SW_TTBR0_PAN (likely Linux v4.9 Catalin's series) | |
| v8.1 (defined since December 2014) | hardware PAN (none shipping) | |
| x86 | pre-late-Broadwell | nothing (could use PCID?) |
| Broadwell+ (since October 2014) | hardware PAN (SMAP) | |
| s/390 | hardware PAN (Address Spaces) | |
| powerpc | nothing? | |
| MIPS | nothing (could use ASID switching?) | |