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CONFIG_DEFAULT_MMAP_MIN_ADDR: Low address space to protect from user allocation

General informations

The Linux kernel configuration item CONFIG_DEFAULT_MMAP_MIN_ADDR:

Help text

This is the portion of low virtual memory which should be protected from userspace allocation. Keeping a user from writing to low pages can help reduce the impact of kernel NULL pointer bugs.

For most ppc64 and x86 users with lots of address space a value of 65536 is reasonable and should cause no problems. On arm and other archs it should not be higher than 32768. Programs which use vm86 functionality or have some need to map this low address space will need CAP_SYS_RAWIO or disable this protection by setting the value to 0.

This value can be changed after boot using the /proc/sys/vm/mmap_min_addr tunable.



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