CVE-2024-57945 Information

Description

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 page’s 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 page’s physical address is not (phys_ram_base » PAGE_SHIFT) then we get an va below VMEMMAP_START when calculating va for it’s 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.

Reference

https://git.kernel.org/stable/c/a4a7ac3d266008018f05fae53060fcb331151a14 https://git.kernel.org/stable/c/d2bd51954ac8377c2f1eb1813e694788998add66 https://git.kernel.org/stable/c/f754f27e98f88428aaf6be6e00f5cbce97f62d4b