This is a note to let you know that I've just added the patch titled
mm/secretmem: fix GUP-fast succeeding on secretmem folios
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-secretmem-fix-gup-fast-succeeding-on-secretmem-folios.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 65291dcfcf8936e1b23cfd7718fdfde7cfaf7706 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@xxxxxxxxxx>
Date: Tue, 26 Mar 2024 15:32:08 +0100
Subject: mm/secretmem: fix GUP-fast succeeding on secretmem folios
From: David Hildenbrand <david@xxxxxxxxxx>
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@xxxxxxxxxx
Fixes: 1507f51255c9 ("mm: introduce memfd_secret system call to create "secret" memory areas")
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reported-by: xingwei lee <xrivendell7@xxxxxxxxx>
Reported-by: yue sun <samsun1006219@xxxxxxxxx>
Closes: https://lore.kernel.org/lkml/CABOYnLyevJeravW=QrH0JUPYEcDN160aZFb7kwndm-J2rmz0HQ@xxxxxxxxxxxxxx/
Debugged-by: Miklos Szeredi <miklos@xxxxxxxxxx>
Tested-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Reviewed-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/secretmem.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/include/linux/secretmem.h
+++ b/include/linux/secretmem.h
@@ -13,10 +13,10 @@ static inline bool folio_is_secretmem(st
/*
* Using folio_mapping() is quite slow because of the actual call
* instruction.
- * 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 (folio_test_large(folio) || !folio_test_lru(folio))
+ if (folio_test_large(folio))
return false;
mapping = (struct address_space *)
Patches currently in stable-queue which might be from david@xxxxxxxxxx are
queue-6.8/selftests-mm-include-strings.h-for-ffsl.patch
queue-6.8/mm-secretmem-fix-gup-fast-succeeding-on-secretmem-folios.patch
queue-6.8/x86-mm-pat-fix-vm_pat-handling-in-cow-mappings.patch
