CVE-2026-98262ata: libahci: clear PxCLBU and PxFBU for AHCI_HFLAG_32BIT_ONLY

Official description

In the Linux kernel, the following vulnerability has been resolved: ata: libahci: clear PxCLBU and PxFBU for AHCI_HFLAG_32BIT_ONLY A user reported that commit 105c42566a55 ("ata: ahci: force 32-bit DMA for JMicron JMB582/JMB585") made the JMicron JMB585 unusable on his board. The failure is seen as soon as the ahci driver is probed, and booting with iommu=off does not solve the problem. Looking at the AHCI specification, PxCLBU and PxFBU are both read only '0' for HBAs that do not support 64-bit addressing. For HBAs that do support 64-bit addressing, the registers are read write, with a reset value that is Implementation Specific. When using the AHCI_HFLAG_32BIT_ONLY flag, the HBA does support 64-bit addressing, and a 32-bit DMA mask is set by simply clearing HOST_CAP_64. Thus, in this case, we need to explicitly clear the registers to 0.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/0191c9ff23ef1678dbfb5ad253a2dee92feb5d71
• https://git.kernel.org/stable/c/8f510f68208a1f673d7c7234a687be4671490e9c
• https://git.kernel.org/stable/c/4719424bb7cb9f20b73986bcb72dd528f0e5c6eb
• https://git.kernel.org/stable/c/a5a8b4737f68bbac8aa0685af0c8921e6003c22b
• https://git.kernel.org/stable/c/b28a17d4a9bb0aa38b48681c3927b012ba40eabe
• https://git.kernel.org/stable/c/b691a3e244278362e552439d6d3ee5a5d3703488
• https://git.kernel.org/stable/c/7912ad8fb5233bb8cfe21d50df639c7f4854ff9d
• https://git.kernel.org/stable/c/82e47533221d4746947b74d2e79a478c36c6433a