CVE-2021-47491 Information

Description

In the Linux kernel the following vulnerability has been resolved:

mm: khugepaged: skip huge page collapse for special files

The read-only THP for filesystems will collapse THP for files opened readonly and mapped with VM_EXEC. The intended usecase is to avoid TLB misses for large text segments. But it doesn’t restrict the file types so a THP could be collapsed for a non-regular file for example block device if it is opened readonly and mapped with EXEC permission. This may cause bugs like [1] and [2].

This is definitely not the intended usecase so just collapse THP for regular files in order to close the attack surface.

[shy828301@gmail.com: fix vm_file check [3]]

Reference

https://git.kernel.org/stable/c/6d67b2a73b8e3a079c355bab3c1aef7d85a044b8 https://git.kernel.org/stable/c/5fcb6fce74ffa614d964667110cf1a516c48c6d9 https://git.kernel.org/stable/c/a4aeaa06d45e90f9b279f0b09de84bd00006e733