powerpc/kasan: Fix addr error caused by page alignment

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: powerpc/kasan: Fix addr error caused by page alignment In kasan_init_region, when k_start is not page aligned, at the begin of for loop, k_cur = k_start & PAGE_MASK is less than k_start, and then `va = block + k_cur - k_start` is less than block, the addr va is invalid, because the memory address space from va to block is not alloced by memblock_alloc, which will not be reserved by memblock_reserve later, it will be used by other places. As a result, memory overwriting occurs. for example: int __init __weak kasan_init_region(void *start, size_t size) { [...] /* if say block(dcd97000) k_start(feef7400) k_end(feeff3fe) */ block = memblock_alloc(k_end - k_start, PAGE_SIZE); [...] for (k_cur = k_start & PAGE_MASK; k_cur < k_end; k_cur += PAGE_SIZE) { /* at the begin of for loop * block(dcd97000) va(dcd96c00) k_cur(feef7000) k_start(feef7400) * va(dcd96c00) is less than block(dcd97000), va is invalid */ void *va = block + k_cur - k_start; [...] } [...] } Therefore, page alignment is performed on k_start before memblock_alloc() to ensure the validity of the VA address.

References

• https://git.kernel.org/stable/c/230e89b5ad0a33f530a2a976b3e5e4385cb27882
• https://git.kernel.org/stable/c/2738e0aa2fb24a7ab9c878d912dc2b239738c6c6
• https://git.kernel.org/stable/c/0c09912dd8387e228afcc5e34ac5d79b1e3a1058
• https://git.kernel.org/stable/c/0516c06b19dc64807c10e01bb99b552bdf2d7dbe
• https://git.kernel.org/stable/c/70ef2ba1f4286b2b73675aeb424b590c92d57b25
• https://git.kernel.org/stable/c/4a7aee96200ad281a5cc4cf5c7a2e2a49d2b97b0