In the Linux kernel, the following vulnerability has been resolved: ARM: 9481/2: breakpoint: CFI...

In the Linux kernel, the following vulnerability has been resolved:

ARM: 9481/2: breakpoint: CFI breakpoints only on demand

This removes the stub hw_breakpoint_cfi_handler() from ARM, making it not steal breakpoint type 0x03 (ARM_ENTRY_CFI_BREAKPOINT) unless CFI is actively used in the kernel.

When not instrumenting with CFI, or when a breakpoint is issued in userspace, we fall through to return 1 from hw_breakpoint_pending() "unhandled fault" so userspace can make use of this breakpoint.

Tested with LKDTM and this command line: echo CFI_FORWARD_PROTO > /sys/kernel/debug/provoke-crash/DIRECT still works as expected.