Exploit Methods/Userspace data usage

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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
v8.0 future: CONFIG_ARM64_SW_TTBR0_PAN (Catalin's series)
v8.1 (since December 2014) hardware PAN
x86 pre-late-Broadwell nothing
Broadwell+ (since October 2014) hardware PAN (SMAP)
s/390 hardware PAN (Address Spaces)
powerpc nothing?
MIPS nothing (could use ASID switching?)
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