From 6564b014af92b677c1f07c44d7f5b595d589cf6e Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Tue, 26 Mar 2024 15:32:08 +0100 Subject: [PATCH] mm/secretmem: fix GUP-fast succeeding on secretmem folios commit 65291dcfcf8936e1b23cfd7718fdfde7cfaf7706 upstream. folio_is_secretmem() currently relies on secretmem folios being LRU folios, to save some cycles. However, folios might reside in a folio batch without the LRU flag set, or temporarily have their LRU flag cleared. Consequently, the LRU flag is unreliable for this purpose. In particular, this is the case when secretmem_fault() allocates a fresh page and calls filemap_add_folio()->folio_add_lru(). The folio might be added to the per-cpu folio batch and won't get the LRU flag set until the batch was drained using e.g., lru_add_drain(). Consequently, folio_is_secretmem() might not detect secretmem folios and GUP-fast can succeed in grabbing a secretmem folio, crashing the kernel when we would later try reading/writing to the folio, because the folio has been unmapped from the directmap. Fix it by removing that unreliable check. Link: https://lkml.kernel.org/r/20240326143210.291116-2-david@redhat.com Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas") Signed-off-by: David Hildenbrand Reported-by: xingwei lee Reported-by: yue sun Closes: https://lore.kernel.org/lkml/CABOYnLyevJeravW=QrH0JUPYEcDN160aZFb7kwndm-J2rmz0HQ@mail.gmail.com/ Debugged-by: Miklos Szeredi Tested-by: Miklos Szeredi Reviewed-by: Mike Rapoport (IBM) Cc: Lorenzo Stoakes Cc: Signed-off-by: Andrew Morton Signed-off-by: David Hildenbrand Signed-off-by: Greg Kroah-Hartman --- include/linux/secretmem.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h index 988528b5da43..48ffe325184c 100644 --- a/include/linux/secretmem.h +++ b/include/linux/secretmem.h @@ -14,10 +14,10 @@ static inline bool page_is_secretmem(struct page *page) * Using page_mapping() is quite slow because of the actual call * instruction and repeated compound_head(page) inside the * page_mapping() function. - * We know that secretmem pages are not compound and LRU so we can + * We know that secretmem pages are not compound, so we can * save a couple of cycles here. */ - if (PageCompound(page) || !PageLRU(page)) + if (PageCompound(page)) return false; mapping = (struct address_space *)