CVE-2026-98923arm64: io: Reject non-user protection in ioremap_prot()

Official description

In the Linux kernel, the following vulnerability has been resolved: arm64: io: Reject non-user protection in ioremap_prot() Mapping a stack-top page via /dev/mem with PROT_NONE and then reading that process's /proc/<pid>/cmdline triggers a spurious WARN in ioremap_prot() through generic_access_phys(): WARNING: ./arch/arm64/include/asm/io.h:275 at generic_access_phys Call trace: generic_access_phys+0x1c8/0x228 (P) __access_remote_vm+0x2b4/0x398 access_remote_vm+0x14/0x30 get_mm_cmdline+0xf8/0x2a0 proc_pid_cmdline_read+0x68/0x120 generic_access_phys() passes the protection derived from the user PTE to ioremap_prot(). On arm64, a PROT_NONE mapping is represented by a present-invalid PTE, so pte_present() still returns true and the protection reaches ioremap_prot(). A PROT_NONE mapping does not have PTE_USER, causing the existing WARN_ON_ONCE() in ioremap_prot() to fire even though this is a valid user mapping. Execute-only mappings have the same issue and must not be readable through this path either. ioremap_prot() should therefore reject protection values without PTE_USER without warning. This makes the access fail cleanly for PROT_NONE and execute-only mappings while retaining the existing user-protection contract.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/fddc90d4af4550af410f52d11bbf6b5f36443838
• https://git.kernel.org/stable/c/0b04af3d88bb7fc69b2d92457890608860e42365
• https://git.kernel.org/stable/c/b17aa4955e3a694c663ebe99626e4c76ca4f7cfb
• https://git.kernel.org/stable/c/9b583795feb51f8d50203228d001760d1344ef01
• https://git.kernel.org/stable/c/bb756b11ad63832ebee58caf9e8f9381eaecff9f