iommu/amd: Fix potential out-of-bounds read in iommu_mmio_show

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: iommu/amd: Fix potential out-of-bounds read in iommu_mmio_show In iommu_mmio_write(), it validates the user-provided offset with the check: `iommu->dbg_mmio_offset > iommu->mmio_phys_end - 4`. This assumes a 4-byte access. However, the corresponding show handler, iommu_mmio_show(), uses readq() to perform an 8-byte (64-bit) read. If a user provides an offset equal to `mmio_phys_end - 4`, the check passes, and will lead to a 4-byte out-of-bounds read. Fix this by adjusting the boundary check to use sizeof(u64), which corresponds to the size of the readq() operation.

References

• https://git.kernel.org/stable/c/b959df804c33913dbfdb90750f2d693502b3d126
• https://git.kernel.org/stable/c/0ec4aaf5f3f559716a6559f3d6d9616e9470bed6
• https://git.kernel.org/stable/c/a0c7005333f9a968abb058b1d77bbcd7fb7fd1e7