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65291dcfcf
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: 1507f51255 ("mm: introduce memfd_secret system call to create "secret" memory areas")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: xingwei lee <xrivendell7@gmail.com>
Reported-by: yue sun <samsun1006219@gmail.com>
Closes: https://lore.kernel.org/lkml/CABOYnLyevJeravW=QrH0JUPYEcDN160aZFb7kwndm-J2rmz0HQ@mail.gmail.com/
Debugged-by: Miklos Szeredi <miklos@szeredi.hu>
Tested-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
53 lines
1.1 KiB
C
53 lines
1.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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#ifndef _LINUX_SECRETMEM_H
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#define _LINUX_SECRETMEM_H
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#ifdef CONFIG_SECRETMEM
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extern const struct address_space_operations secretmem_aops;
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static inline bool folio_is_secretmem(struct folio *folio)
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{
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struct address_space *mapping;
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/*
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* Using folio_mapping() is quite slow because of the actual call
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* instruction.
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* We know that secretmem pages are not compound, so we can
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* save a couple of cycles here.
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*/
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if (folio_test_large(folio))
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return false;
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mapping = (struct address_space *)
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((unsigned long)folio->mapping & ~PAGE_MAPPING_FLAGS);
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if (!mapping || mapping != folio->mapping)
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return false;
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return mapping->a_ops == &secretmem_aops;
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}
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bool vma_is_secretmem(struct vm_area_struct *vma);
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bool secretmem_active(void);
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#else
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static inline bool vma_is_secretmem(struct vm_area_struct *vma)
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{
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return false;
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}
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static inline bool folio_is_secretmem(struct folio *folio)
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{
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return false;
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}
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static inline bool secretmem_active(void)
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{
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return false;
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}
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#endif /* CONFIG_SECRETMEM */
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#endif /* _LINUX_SECRETMEM_H */
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