From: Ruihan Li <lrh2000@xxxxxxxxxx> commit 44d0fb387b53e56c8a050bac5c7d460e21eb226f upstream. The current uses of PageAnon in page table check functions can lead to type confusion bugs between struct page and slab [1], if slab pages are accidentally mapped into the user space. This is because slab reuses the bits in struct page to store its internal states, which renders PageAnon ineffective on slab pages. Since slab pages are not expected to be mapped into the user space, this patch adds BUG_ON(PageSlab(page)) checks to make sure that slab pages are not inadvertently mapped. Otherwise, there must be some bugs in the kernel. Reported-by: syzbot+fcf1a817ceb50935ce99@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lore.kernel.org/lkml/000000000000258e5e05fae79fc1@xxxxxxxxxx/ [1] Fixes: df4e817b7108 ("mm: page table check") Cc: <stable@xxxxxxxxxxxxxxx> # 5.17 Signed-off-by: Ruihan Li <lrh2000@xxxxxxxxxx> Acked-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> Link: https://lore.kernel.org/r/20230515130958.32471-5-lrh2000@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/page-flags.h | 6 ++++++ mm/page_table_check.c | 6 ++++++ 2 files changed, 12 insertions(+) --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -631,6 +631,12 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemma * Please note that, confusingly, "page_mapping" refers to the inode * address_space which maps the page from disk; whereas "page_mapped" * refers to user virtual address space into which the page is mapped. + * + * For slab pages, since slab reuses the bits in struct page to store its + * internal states, the page->mapping does not exist as such, nor do these + * flags below. So in order to avoid testing non-existent bits, please + * make sure that PageSlab(page) actually evaluates to false before calling + * the following functions (e.g., PageAnon). See mm/slab.h. */ #define PAGE_MAPPING_ANON 0x1 #define PAGE_MAPPING_MOVABLE 0x2 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -69,6 +69,8 @@ static void page_table_check_clear(struc page = pfn_to_page(pfn); page_ext = page_ext_get(page); + + BUG_ON(PageSlab(page)); anon = PageAnon(page); for (i = 0; i < pgcnt; i++) { @@ -105,6 +107,8 @@ static void page_table_check_set(struct page = pfn_to_page(pfn); page_ext = page_ext_get(page); + + BUG_ON(PageSlab(page)); anon = PageAnon(page); for (i = 0; i < pgcnt; i++) { @@ -131,6 +135,8 @@ void __page_table_check_zero(struct page struct page_ext *page_ext; unsigned long i; + BUG_ON(PageSlab(page)); + page_ext = page_ext_get(page); BUG_ON(!page_ext); for (i = 0; i < (1ul << order); i++) {
