CVE-2024-57945

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

riscv: mm: Fix the out of bound issue of vmemmap address

In sparse vmemmap model, the virtual address of vmemmap is calculated as: ((struct page *)VMEMMAP_START - (phys_ram_base » PAGE_SHIFT)). And the struct pages va can be calculated with an offset: (vmemmap + (pfn)).

However, when initializing struct pages, kernel actually starts from the first page from the same section that phys_ram_base belongs to. If the first pages physical address is not (phys_ram_base » PAGE_SHIFT), then we get an va below VMEMMAP_START when calculating va for its struct page.

For example, if phys_ram_base starts from 0x82000000 with pfn 0x82000, the first page in the same section is actually pfn 0x80000. During init_unavailable_range(), we will initialize struct page for pfn 0x80000 with virtual address ((struct page *)VMEMMAP_START - 0x2000), which is below VMEMMAP_START as well as PCI_IO_END.

This commit fixes this bug by introducing a new variable vmemmap_start_pfn which is aligned with memory section size and using it to calculate vmemmap address instead of phys_ram_base.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/92f08673d3f1893191323572f60e3c62f2e57c2f
• https://git.kernel.org/stable/c/a4a7ac3d266008018f05fae53060fcb331151a14
• https://git.kernel.org/stable/c/d2bd51954ac8377c2f1eb1813e694788998add66
• https://git.kernel.org/stable/c/f754f27e98f88428aaf6be6e00f5cbce97f62d4b
• https://lists.debian.org/debian-lts-announce/2025/08/msg00010.html