CVE-2026-63939

Description

In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Compute the correct max length of the in-GHCB scratch area When setting the length of the GHCB scratch area, and the area is in the GHCB shared buffer, set the effective length of the scratch area to the max possible size given the start of the guest-provided pointer, and the end of the shared buffer. The code was "fine" when first introduced, as KVM doesn't consult the length of the buffer when emulating MMIO, because the passed in @len always specifies the *max* size required. But for PSC requests, the incoming @len is just the minimum length (to process the header), and KVM needs to know the full size of the scratch area to avoid buffer overflows (spoiler alert). Opportunistically rename @len => @min_len to better reflect its role.

CVSS 3.1 breakdown

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

• https://git.kernel.org/stable/c/5867d7e202e09f037cefe77f7af4413c7c0fa088
• https://git.kernel.org/stable/c/6644565527c4c5f507088b1c9ddf72de47790b68
• https://git.kernel.org/stable/c/6ca9400d36005ffdca25f80186bea781c7e1dc4c
• https://git.kernel.org/stable/c/9f0a9e780f02c02d025a190f1885e1d1d73b87bd

Frequently asked