CVE-2024-35872 Information

Description

In the Linux kernel the following vulnerability has been resolved:

mm/secretmem: fix GUP-fast succeeding on secretmem folios

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.

Reference

https://git.kernel.org/stable/c/6564b014af92b677c1f07c44d7f5b595d589cf6e https://git.kernel.org/stable/c/9c2b4b657739ecda38e3b383354a29566955ac48 https://git.kernel.org/stable/c/43fad1d0284de30159661d0badfc3cbaf7e6f8f8 https://git.kernel.org/stable/c/201e4aaf405dfd1308da54448654053004c579b5 https://git.kernel.org/stable/c/65291dcfcf8936e1b23cfd7718fdfde7cfaf7706