iommu: Don't reserve 0-length IOVA region

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: iommu: Don't reserve 0-length IOVA region When the bootloader/firmware doesn't setup the framebuffers, their address and size are 0 in "iommu-addresses" property. If IOVA region is reserved with 0 length, then it ends up corrupting the IOVA rbtree with an entry which has pfn_hi < pfn_lo. If we intend to use display driver in kernel without framebuffer then it's causing the display IOMMU mappings to fail as entire valid IOVA space is reserved when address and length are passed as 0. An ideal solution would be firmware removing the "iommu-addresses" property and corresponding "memory-region" if display is not present. But the kernel should be able to handle this by checking for size of IOVA region and skipping the IOVA reservation if size is 0. Also, add a warning if firmware is requesting 0-length IOVA region reservation.

References

• https://git.kernel.org/stable/c/98b8a550da83cc392a14298c4b3eaaf0332ae6ad
• https://git.kernel.org/stable/c/5e23e283910c9f30248732ae0770bcb0c9438abf
• https://git.kernel.org/stable/c/bb57f6705960bebeb832142ce9abf43220c3eab1