linux-kernel - [PATCH v1 1/3] mm/secretmem: fix GUP-fast succeeding on secretmem folios

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Date: Mon, 25 Mar 2024 14:41:12 +0100
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Rapoport <rppt@...nel.org>,
	Miklos Szeredi <mszeredi@...hat.com>,
	Lorenzo Stoakes <lstoakes@...il.com>,
	xingwei lee <xrivendell7@...il.com>,
	yue sun <samsun1006219@...il.com>,
	Miklos Szeredi <miklos@...redi.hu>,
	stable@...r.kernel.org
Subject: [PATCH v1 1/3] mm/secretmem: fix GUP-fast succeeding on secretmem folios

folio_is_secretmem() states that secretmem folios cannot be LRU folios:
so we may only exit early if we find an LRU folio. Yet, we exit early if
we find a folio that is not a secretmem folio.

Consequently, folio_is_secretmem() fails to detect secretmem folios and,
therefore, we can succeed in grabbing a secretmem folio during GUP-fast,
crashing the kernel when we later try reading/writing to the folio, because
the folio has been unmapped from the directmap.

Reported-by: xingwei lee <xrivendell7@...il.com>
Reported-by: yue sun <samsun1006219@...il.com>
Closes: https://lore.kernel.org/lkml/CABOYnLyevJeravW=QrH0JUPYEcDN160aZFb7kwndm-J2rmz0HQ@mail.gmail.com/
Debugged-by: Miklos Szeredi <miklos@...redi.hu>
Reviewed-by: Mike Rapoport (IBM) <rppt@...nel.org>
Tested-by: Miklos Szeredi <mszeredi@...hat.com>
Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas")
Cc: <stable@...r.kernel.org>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/linux/secretmem.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/secretmem.h b/include/linux/secretmem.h
index 35f3a4a8ceb1..6996f1f53f14 100644
--- a/include/linux/secretmem.h
+++ b/include/linux/secretmem.h
@@ -16,7 +16,7 @@ static inline bool folio_is_secretmem(struct folio *folio)
 	 * We know that secretmem pages are not compound and LRU so we can
 	 * save a couple of cycles here.
 	 */
-	if (folio_test_large(folio) || !folio_test_lru(folio))
+	if (folio_test_large(folio) || folio_test_lru(folio))
 		return false;
 
 	mapping = (struct address_space *)
-- 
2.43.2