CVE-2026-98639

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

KVM: riscv: Fix NACL hfence entry update order

The SBI v3.0 specification (section 15.1.2) requires a nested HFENCE

entry to be populated as follows:

1) find an unused entry with Config.Pending == 0

2) update the Page_Number and Page_Count words

3) update the Config word with Config.Pending set

__kvm_riscv_nacl_hfence() writes the Config word first, so the SBI

implementation (or NACL hardware) can observe a pending entry with

pnum/pcount values left over from the previous use of that entry,

resulting in incorrect TLB flush ranges.

Write pnum and pcount first and the Config word last. Since the

consumer is an external agent on coherent shared memory, use

WRITE_ONCE() to stop the compiler from reordering the stores and

smp_wmb() to make the parameter words globally visible before the

Pending bit is set.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References