| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2021-47491: mm: khugepaged: skip huge page collapse for special files |
| |
| 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]] |
| |
| The Linux kernel CVE team has assigned CVE-2021-47491 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.4 with commit 99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 and fixed in 5.10.78 with commit 6d67b2a73b8e3a079c355bab3c1aef7d85a044b8 |
| Issue introduced in 5.4 with commit 99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 and fixed in 5.14.16 with commit 5fcb6fce74ffa614d964667110cf1a516c48c6d9 |
| Issue introduced in 5.4 with commit 99cb0dbd47a15d395bf3faa78dc122bc5efe3fc0 and fixed in 5.15 with commit a4aeaa06d45e90f9b279f0b09de84bd00006e733 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2021-47491 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| mm/khugepaged.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/6d67b2a73b8e3a079c355bab3c1aef7d85a044b8 |
| https://git.kernel.org/stable/c/5fcb6fce74ffa614d964667110cf1a516c48c6d9 |
| https://git.kernel.org/stable/c/a4aeaa06d45e90f9b279f0b09de84bd00006e733 |
