From df9bc25d13c146a3979015f73ab9b5d406ca7ae1 Mon Sep 17 00:00:00 2001 From: Ruihan Li Date: Mon, 15 May 2023 21:09:58 +0800 Subject: [PATCH] mm: page_table_check: Ensure user pages are not slab pages 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@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/000000000000258e5e05fae79fc1@google.com/ [1] Fixes: df4e817b7108 ("mm: page table check") Cc: # 5.17 Signed-off-by: Ruihan Li Acked-by: Pasha Tatashin Link: https://lore.kernel.org/r/20230515130958.32471-5-lrh2000@pku.edu.cn Signed-off-by: Greg Kroah-Hartman --- include/linux/page-flags.h | 6 ++++++ mm/page_table_check.c | 6 ++++++ 2 files changed, 12 insertions(+) diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 0b0ae50..59314d2 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -631,6 +631,12 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted) * 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 diff --git a/mm/page_table_check.c b/mm/page_table_check.c index 433dbce..4d05065 100644 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -69,6 +69,8 @@ static void page_table_check_clear(struct mm_struct *mm, unsigned long addr, 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 mm_struct *mm, unsigned long addr, 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 *page, unsigned int order) 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++) { -- 2.7.4