# CVE-2025-40245: nios2: ensure that memblock.current_limit is set when setting pfn limits

CVE-2025-40245 is fixed in linux on 1 platform, first by DEBIAN-CVE-2025-40245, released December 4, 2025. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2025-40245
- Priority: High
- CVSS: 7.8 (Moderate)
- EPSS: 0.0016
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Dec 4, 2025
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-40245

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 12.15 (bookworm) | 6.1.158-1 | [DEBIAN-CVE-2025-40245](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40245.md) | Dec 4, 2025 |
| Linux | linux Debian 13.5 (trixie) | 6.12.57-1 | [DEBIAN-CVE-2025-40245](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40245.md) | Dec 4, 2025 |
| Linux | linux Debian 14 | 6.17.6-1 | [DEBIAN-CVE-2025-40245](https://patchblox.com/security/data/fix/linux/debian-cve-2025-40245.md) | Dec 4, 2025 |

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