KSM merges identical anonymous pages across processes. An attacker who can place chosen page-sized content in a victim's memory can detect the merge through the timing of the resulting copy-on-write fault, and so leak memory contents.
There is no upstream fix; removing the side channel means removing deduplication. Distribution trackers describe it the same way - Debian marks src:linux unfixed with "Inherent design limitation, can be avoided by not using KSM", Red Hat closed its bug WONTFIX, and Ubuntu records no upstream fix as of 2024-06-17: https://security-tracker.debian.org/tracker/CVE-2021-3714 https://bugzilla.redhat.com/show_bug.cgi?id=1931327 https://ubuntu.com/security/CVE-2021-3714 Exposure requires two runtime opt-ins: ksmd must be started by the administrator (ksm_run defaults to KSM_RUN_STOP in mm/ksm.c) and memory is only eligible when a process asks with madvise(MADV_MERGEABLE) or prctl(PR_SET_MEMORY_MERGE). CONFIG_KSM=y is set in yocto-kernel-cache (bsp/intel-x86 and the paravirt_kvm fragments), so this is not a configuration exclusion. CC: Paul Barker <[email protected]> AI-Generated: Uses Claude (claude-opus-5) Signed-off-by: Junjie Cao <[email protected]> --- v3: - use "unpatched" instead of "upstream-wontfix": the WONTFIX is a distribution position, not an upstream one v2: https://lore.kernel.org/openembedded-core/[email protected]/ meta/recipes-kernel/linux/cve-exclusion.inc | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/meta/recipes-kernel/linux/cve-exclusion.inc b/meta/recipes-kernel/linux/cve-exclusion.inc index 5ed4a00..af3576d 100644 --- a/meta/recipes-kernel/linux/cve-exclusion.inc +++ b/meta/recipes-kernel/linux/cve-exclusion.inc @@ -199,3 +199,10 @@ CVE_STATUS[CVE-2025-71145] = "cpe-stable-backport: Fixed from v6.18.3" # https://ubuntu.com/security/CVE-2019-14899 CVE_STATUS[CVE-2019-14899] = "unpatched: consequence of the default weak \ host model, no upstream kernel fix, mitigated by firewall configuration" + +# Timing side channel inherent to KSM page deduplication. Reachable only +# when ksmd is started (/sys/kernel/mm/ksm/run defaults to 0) and the +# workload opts in via MADV_MERGEABLE or prctl(PR_SET_MEMORY_MERGE). +# https://security-tracker.debian.org/tracker/CVE-2021-3714 +CVE_STATUS[CVE-2021-3714] = "unpatched: timing side channel inherent to \ +KSM page deduplication, only reachable when KSM is enabled and opted into" -- 2.43.0
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