iommu/riscv: prevent NULL deref in iova_to_phys

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: iommu/riscv: prevent NULL deref in iova_to_phys The riscv_iommu_pte_fetch() function returns either NULL for unmapped/never-mapped iova, or a valid leaf pte pointer that requires no further validation. riscv_iommu_iova_to_phys() failed to handle NULL returns. Prevent null pointer dereference in riscv_iommu_iova_to_phys(), and remove the pte validation.

References

• https://git.kernel.org/stable/c/220c491490255b656672bb572b18460cd9155926
• https://git.kernel.org/stable/c/99d4d1a070870aa08163af8ce0522992b7f35d8c