UBUNTU-CVE-2026-98551: Medium severity ubuntu/linux-hwe-edge vulnerability
In the Linux kernel, the following vulnerability has been resolved: perf/core: Fill branch entries with a single assignment perfclearbranchentrybitfields() clears the bitfields of struct perfbranchentry one by one and leaves from/to alone, since callers overwrite those straight away. The list has to be kept in sync with the struct by hand and has already fallen behind: newtype and priv were added to perfbranchentry and never added here. Only BRBE writes those two, and neither for every record. brbesetperfentrytype() leaves newtype alone for a branch type it does not recognise, and priv is not set for source-only records. armpmuv3.c allocates the per-CPU branch stack with kmalloc(), so such a record reaches userspace with whatever the slot held: uninitialised kmalloc() data on the first pass over the buffer, the previous record's values after that. Nothing under arch/x86/events/ writes either field, so only arm64 is affected. Assign the whole entry at each site instead. Everything not named is then zero, and there is no list to keep in sync. The bitfields add up to exactly 64 bits, so the struct has no padding to leave undefined. perfclearbranchentrybitfields() has no callers left, so remove it. perfentryfrombrberegset() assigns an empty literal instead, since it fills from/to conditionally. PERFBRSPECNA is 0, so dropping the explicit spec assignment changes nothing.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
ubuntu/linux-hwe-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42~24.04.1 - Upgrade
Upgrade
ubuntu/linux-riscv-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1~24.04.1 - Upgrade
Upgrade
ubuntu/linuxto a version that resolves this vulnerability.Fixed in 7.0.0-42.42 - Upgrade
Upgrade
ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 7.0.0-1016.17 - Upgrade
Upgrade
ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 7.0.0-1016.18 - Upgrade
Upgrade
ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
Upgrade
ubuntu/linux-oem-7.0to a version that resolves this vulnerability.Fixed in 7.0.0-1017.17 - Upgrade
Upgrade
ubuntu/linux-oracleto a version that resolves this vulnerability.Fixed in 7.0.0-1015.16 - Upgrade
Upgrade
ubuntu/linux-riscvto a version that resolves this vulnerability.Fixed in 7.0.0-42.42.1 - Remove
Remove
perf_clear_branch_entry_bitfields()from your environment.Remove perf_clear_branch_entry_bitfields(), which has no callers left.
- Configuration
Assign the whole perf_branch_entry at each site using an empty literal so all fields, including from, to, new_type, and priv, are initialized before conditional assignments.
Linux kernel perf/core perf_branch_entry initialization = empty literal
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
The issue affects arm64 systems using the BRBE performance-monitoring path. The provided kernel description states that x86 event code does not write the affected fields, so x86 is not affected.
What access does an attacker need to exploit it?
An attacker needs local access with low privileges and must be able to obtain affected perf branch records. The exposure occurs when BRBE does not set the new_type field for an unrecognized branch type or does not set priv for source-only records.
What data could be exposed?
Affected branch records can contain uninitialized kmalloc data on the first pass through the per-CPU branch buffer. On later passes, the fields may instead disclose values left by a previous branch record.