{"id":"CVE-2025-40245","state":"PUBLISHED","title":"nios2: ensure that memblock.current_limit is set when setting pfn limits","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnios2: ensure that memblock.current_limit is set when setting pfn limits\n\nOn nios2, with CONFIG_FLATMEM set, the kernel relies on\nmemblock_get_current_limit() to determine the limits of mem_map, in\nparticular for max_low_pfn.\nUnfortunately, memblock.current_limit is only default initialized to\nMEMBLOCK_ALLOC_ANYWHERE at this point of the bootup, potentially leading\nto situations where max_low_pfn can erroneously exceed the value of\nmax_pfn and, thus, the valid range of available DRAM.\n\nThis can in turn cause kernel-level paging failures, e.g.:\n\n[   76.900000] Unable to handle kernel paging request at virtual address 20303000\n[   76.900000] ea = c0080890, ra = c000462c, cause = 14\n[   76.900000] Kernel panic - not syncing: Oops\n[   76.900000] ---[ end Kernel panic - not syncing: Oops ]---\n\nThis patch fixes this by pre-calculating memblock.current_limit\nbased on the upper limits of the available memory ranges via\nadjust_lowmem_bounds, a simplified version of the equivalent\nimplementation within the arm architecture.","publishedAt":"2025-12-04T15:31:34.142Z","updatedAt":"2026-08-05T12:08:49.485Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"25f09699edd360b534ccae16bc276c3b52c471f3","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"5c3e38a367822f036227dd52bac82dc4a05157e2","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"b1ec9faef7e36269ca3ec890972a78effbaeb975","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"90f5f715550e07cd6a51f80fc3f062d832c8c997","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"8912814f14e298b83df072fecc1f7ed1b63b1b2c","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"a20b83cf45be2057f3d073506779e52c7fa17f94","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/nios2/kernel/setup.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.12","versionType":"semver"},{"version":"5.15.196","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.158","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.115","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.56","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.17.6","status":"unaffected","lessThanOrEqual":"6.17.*","versionType":"semver"},{"version":"6.18","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/nios2/kernel/setup.c"]}],"references":["https://git.kernel.org/stable/c/25f09699edd360b534ccae16bc276c3b52c471f3","https://git.kernel.org/stable/c/5c3e38a367822f036227dd52bac82dc4a05157e2","https://git.kernel.org/stable/c/b1ec9faef7e36269ca3ec890972a78effbaeb975","https://git.kernel.org/stable/c/90f5f715550e07cd6a51f80fc3f062d832c8c997","https://git.kernel.org/stable/c/8912814f14e298b83df072fecc1f7ed1b63b1b2c","https://git.kernel.org/stable/c/a20b83cf45be2057f3d073506779e52c7fa17f94"],"weaknesses":[],"ingestedAt":"2026-10-29T20:09:09.358Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/40xxx/CVE-2025-40245.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-40245","state":"PUBLISHED","datePublished":"2025-12-04T15:31:34.142Z","dateUpdated":"2026-08-05T12:08:49.485Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-04-16T07:20:57.181Z"},"containers":{"cna":{"title":"nios2: ensure that memblock.current_limit is set when setting pfn limits","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnios2: ensure that memblock.current_limit is set when setting pfn limits\n\nOn nios2, with CONFIG_FLATMEM set, the kernel relies on\nmemblock_get_current_limit() to determine the limits of mem_map, in\nparticular for max_low_pfn.\nUnfortunately, memblock.current_limit is only default initialized to\nMEMBLOCK_ALLOC_ANYWHERE at this point of the bootup, potentially leading\nto situations where max_low_pfn can erroneously exceed the value of\nmax_pfn and, thus, the valid range of available DRAM.\n\nThis can in turn cause kernel-level paging failures, e.g.:\n\n[   76.900000] Unable to handle kernel paging request at virtual address 20303000\n[   76.900000] ea = c0080890, ra = c000462c, cause = 14\n[   76.900000] Kernel panic - not syncing: Oops\n[   76.900000] ---[ end Kernel panic - not syncing: Oops ]---\n\nThis patch fixes this by pre-calculating memblock.current_limit\nbased on the upper limits of the available memory ranges via\nadjust_lowmem_bounds, a simplified version of the equivalent\nimplementation within the arm architecture."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"25f09699edd360b534ccae16bc276c3b52c471f3","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"5c3e38a367822f036227dd52bac82dc4a05157e2","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"b1ec9faef7e36269ca3ec890972a78effbaeb975","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"90f5f715550e07cd6a51f80fc3f062d832c8c997","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"8912814f14e298b83df072fecc1f7ed1b63b1b2c","versionType":"git"},{"version":"7f7bc20bc41a4fbcd2db75b375ac95e5faf958ae","status":"affected","lessThan":"a20b83cf45be2057f3d073506779e52c7fa17f94","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/nios2/kernel/setup.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.12","versionType":"semver"},{"version":"5.15.196","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.158","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.115","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.56","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.17.6","status":"unaffected","lessThanOrEqual":"6.17.*","versionType":"semver"},{"version":"6.18","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/nios2/kernel/setup.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/25f09699edd360b534ccae16bc276c3b52c471f3"},{"url":"https://git.kernel.org/stable/c/5c3e38a367822f036227dd52bac82dc4a05157e2"},{"url":"https://git.kernel.org/stable/c/b1ec9faef7e36269ca3ec890972a78effbaeb975"},{"url":"https://git.kernel.org/stable/c/90f5f715550e07cd6a51f80fc3f062d832c8c997"},{"url":"https://git.kernel.org/stable/c/8912814f14e298b83df072fecc1f7ed1b63b1b2c"},{"url":"https://git.kernel.org/stable/c/a20b83cf45be2057f3d073506779e52c7fa17f94"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The defect is in nios2 `setup_arch()` boot-time memory initialization, and its consequences are realized through local activity — memory allocation and `mmap()`/page-fault paths that call `pfn_valid()`/`pfn_to_page()`. There is no network or remote-peer path to arch/nios2/kernel/setup.c.\nAC:L - `memblock.current_limit` is never set before `find_limits()`, so `max_low_pfn`/`max_mapnr` are unconditionally inflated to ~4 GB of PFNs on every affected nios2 system — the vulnerable state always exists, with no race and no memory-layout luck required. The attacker only needs to map or touch a physical region above DRAM, which is under their control on these FPGA SoCs where peripheral/on-chip-memory windows sit above RAM.\nPR:L - No capability check guards any of it — an ordinary unprivileged process reaching `update_mmu_cache_range()`/`flush_dcache_page()` through a fault on a device or PFNMAP mapping, or simply driving allocation into the bogus PFN range, is sufficient. Embedded nios2 deployments routinely expose UIO/framebuffer device nodes to non-root users.\nUI:N - The attacker performs every step themselves — map the region, touch it, let the fault path run. No action by another user or administrator is needed.\nS:U - The out-of-bounds accesses stay within the kernel's own memory and security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - `pfn_valid()` wrongly approves PFNs with no memmap entry, so `pfn_to_page()` returns a pointer up to tens of megabytes past the end of `mem_map`, and `folio_flush_mapping()`/`flush_aliases()` read and follow that out-of-bounds kernel data as an `address_space`. This is a wide, PFN-indexed out-of-bounds read, far beyond a strictly bounded few bytes.\nI:H - `update_mmu_cache_range()` performs `test_and_set_bit(PG_dcache_clean, &folio->flags.f)` on the out-of-bounds `struct page`, an attacker-positioned out-of-bounds atomic write into arbitrary kernel memory, and then walks a garbage `address_space`/i_mmap tree. Per the OOB-write guidance this is High.\nA:H - The documented, reproduced impact is a fatal kernel paging fault and panic (\"Unable to handle kernel paging request ... Kernel panic - not syncing: Oops\"), and the corrupted low-memory limits can equally cause the allocator and DMA logic to operate on non-existent DRAM. The condition is triggerable repeatedly at will."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:08:49.485Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"5.15.196"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.1.158"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.6.115"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.12.56"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.17.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"6.18"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}