CVE-2024-57883

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

mm: hugetlb: independent PMD page table shared count

The folio refcount may be increased unexpectly through try_get_folio() by

caller such as split_huge_pages. In huge_pmd_unshare(), we use refcount

to check whether a pmd page table is shared. The check is incorrect if

the refcount is increased by the above caller, and this can cause the page

table leaked:

BUG: Bad page state in process sh pfn:109324

page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x66 pfn:0x109324

flags: 0x17ffff800000000(node=0|zone=2|lastcpupid=0xfffff)

page_type: f2(table)

raw: 017ffff800000000 0000000000000000 0000000000000000 0000000000000000

raw: 0000000000000066 0000000000000000 00000000f2000000 0000000000000000

page dumped because: nonzero mapcount

...

CPU: 31 UID: 0 PID: 7515 Comm: sh Kdump: loaded Tainted: G B 6.13.0-rc2master+ #7

Tainted: [B]=BAD_PAGE

Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015

Call trace:

show_stack+0x20/0x38 (C)

dump_stack_lvl+0x80/0xf8

dump_stack+0x18/0x28

bad_page+0x8c/0x130

free_page_is_bad_report+0xa4/0xb0

free_unref_page+0x3cc/0x620

__folio_put+0xf4/0x158

split_huge_pages_all+0x1e0/0x3e8

split_huge_pages_write+0x25c/0x2d8

full_proxy_write+0x64/0xd8

vfs_write+0xcc/0x280

ksys_write+0x70/0x110

__arm64_sys_write+0x24/0x38

invoke_syscall+0x50/0x120

el0_svc_common.constprop.0+0xc8/0xf0

do_el0_svc+0x24/0x38

el0_svc+0x34/0x128

el0t_64_sync_handler+0xc8/0xd0

el0t_64_sync+0x190/0x198

The issue may be triggered by damon, offline_page, page_idle, etc, which

will increase the refcount of page table.

1. The page table itself will be discarded after reporting the

"nonzero mapcount".

2. The HugeTLB page mapped by the page table miss freeing since we

treat the page table as shared and a shared page table will not be

unmapped.

Fix it by introducing independent PMD page table shared count. As

described by comment, pt_index/pt_mm/pt_frag_refcount are used for s390

gmap, x86 pgds and powerpc, pt_share_count is used for x86/arm64/riscv

pmds, so we can reuse the field as pt_share_count.