mm/vmalloc: fix page mapping if vm_area_alloc_pages() with high order fallback to order 0

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mm/vmalloc: fix page mapping if vm_area_alloc_pages() with high order fallback to order 0 The __vmap_pages_range_noflush() assumes its argument pages** contains pages with the same page shift. However, since commit e9c3cda4d86e ("mm, vmalloc: fix high order __GFP_NOFAIL allocations"), if gfp_flags includes __GFP_NOFAIL with high order in vm_area_alloc_pages() and page allocation failed for high order, the pages** may contain two different page shifts (high order and order-0). This could lead __vmap_pages_range_noflush() to perform incorrect mappings, potentially resulting in memory corruption. Users might encounter this as follows (vmap_allow_huge = true, 2M is for PMD_SIZE): kvmalloc(2M, __GFP_NOFAIL|GFP_X) __vmalloc_node_range_noprof(vm_flags=VM_ALLOW_HUGE_VMAP) vm_area_alloc_pages(order=9) ---> order-9 allocation failed and fallback to order-0 vmap_pages_range() vmap_pages_range_noflush() __vmap_pages_range_noflush(page_shift = 21) ----> wrong mapping happens We can remove the fallback code because if a high-order allocation fails, __vmalloc_node_range_noprof() will retry with order-0. Therefore, it is unnecessary to fallback to order-0 here. Therefore, fix this by removing the fallback code.

References

• https://git.kernel.org/stable/c/fd1ffbb50ef4da5e1378a46616b6d7407dc795da
• https://git.kernel.org/stable/c/de7bad86345c43cd040ed43e20d9fad78a3ee59f
• https://git.kernel.org/stable/c/c91618816f4d21fc574d7577a37722adcd4075b2
• https://git.kernel.org/stable/c/61ebe5a747da649057c37be1c37eb934b4af79ca