CVE-2025-40245

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

nios2: ensure that memblock.current_limit is set when setting pfn limits

On nios2, with CONFIG_FLATMEM set, the kernel relies on memblock_get_current_limit() to determine the limits of mem_map, in particular for max_low_pfn. Unfortunately, memblock.current_limit is only default initialized to MEMBLOCK_ALLOC_ANYWHERE at this point of the bootup, potentially leading to situations where max_low_pfn can erroneously exceed the value of max_pfn and, thus, the valid range of available DRAM.

This can in turn cause kernel-level paging failures, e.g.:

[ 76.900000] Unable to handle kernel paging request at virtual address 20303000 [ 76.900000] ea = c0080890, ra = c000462c, cause = 14 [ 76.900000] Kernel panic - not syncing: Oops [ 76.900000] ---[ end Kernel panic - not syncing: Oops ]---

This patch fixes this by pre-calculating memblock.current_limit based on the upper limits of the available memory ranges via adjust_lowmem_bounds, a simplified version of the equivalent implementation within the arm architecture.

This vulnerability does not impact Red Hat Enterprise Linux because it is strictly confined to the Nios II (nios2) processor architecture. Red Hat does not build or distribute kernels for this hardware platform. Consequently, supported enterprise installations do not include the vulnerable architecture-specific setup code and are not at risk.