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CONFIG_X86_IOPL_IOPERM: IOPERM and IOPL Emulation

General informations

The Linux kernel configuration item CONFIG_X86_IOPL_IOPERM:

Help text

This enables the ioperm() and iopl() syscalls which are necessary for legacy applications.

Legacy IOPL support is an overbroad mechanism which allows user space aside of accessing all 65536 I/O ports also to disable interrupts. To gain this access the caller needs CAP_SYS_RAWIO capabilities and permission from potentially active security modules.

The emulation restricts the functionality of the syscall to only allowing the full range I/O port access, but prevents the ability to disable interrupts from user space which would be granted if the hardware IOPL mechanism would be used.

Hardware

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