hardened_malloc/KERNEL_FEATURE_WISHLIST.md

Very important and should be an easy sell:

• improved robustness for high vma count on high memory machines
• much higher vm.max_map_count by default
• work on improving performance and resource usage with high vma count
• add a way to disable the brk heap and have mmap grow upwards like it did in the past (preserving the same high base entropy)

Somewhat important and an easy sell:

• alternative to RLIMIT_AS for accountable mappings only
  • memory control groups are sometimes a better option but there are still users of RLIMIT_AS that are problematic for mitigations or simply fast garbage collector implementations, etc. mapping lots of PROT_NONE memory
• mremap flag to disable unmapping the source mapping
  • also needed by jemalloc for different reasons
  • not needed if the kernel gets first class support for arbitrarily sized guard pages and a virtual memory quarantine feature

Fairly infeasible to land but could reduce overhead and extend coverage of security features to other code directly using mmap:

• first class support for arbitrarily sized guard pages for mmap and mremap to eliminate half of the resulting VMAs and reduce 2 system calls to 1
  • not usable if it doesn't support mremap (shrink, grow, grow via move)
  • not usable if the guard page size is static
  • should support changing guard size for mremap growth via move
  • must be possible to set it up from the process
• virtual memory quarantine
  • must be possible to set it up from the process
• first-class support for aligned mappings with mmap and ideally mremap
  • not usable unless guard page support is provided and of course it has to work with this too