In the Linux kernel, the following vulnerability has been resolved:
mshv_vtl: Check per-CPU register page before mmap
Register-page setup is optional for each CPU. If allocation or registration fails, mshv_vtl_configure_reg_page() warns and leaves that CPU's reg_page NULL, but initial context setup continues successfully. Meanwhile, successful setup on another CPU sets the global mshv_has_reg_page flag.
mshv_vtl_fault() checks this global flag before selecting the requested CPU's register page. With mixed setup results across online CPUs, the check passes even for a CPU with no register page, reaching get_page(NULL) when userspace faults in that mapping.
Check the selected per-CPU register page before taking its reference and return VM_FAULT_SIGBUS if it is absent.
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