Exploit Methods/Userspace data usage

From Linux Kernel Security Subsystem
Revision as of 19:48, 15 September 2016 by KeesCook (talk | contribs) (→‎Mitigations)
Jump to navigation Jump to search

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 segregation: SMAP (x86), PAN (arm, arm64), Domains (arm)
  • emulated PAN (memory segregation 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?)