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 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.