CVE-2026-64186

In the Linux kernel, the following vulnerability has been resolved:

iommu/amd: Remove latent out-of-bounds access in IOMMU debugfs

In iommu_mmio_write() and iommu_capability_write(), the variables

dbg_mmio_offset and dbg_cap_offset are declared as int. However, they

are populated using kstrtou32_from_user(). If a user provides a

sufficiently large value, it can become a negative integer.

Prior to this patch, the AMD IOMMU debugfs implementation was already

protected by different mechanisms.

1. #define OFS_IN_SZ 8 ensures the user string <= 8 bytes, so

e.g. 0xffffffff isn't a valid input.

if (cnt > OFS_IN_SZ)

return -EINVAL;

2. Implicit type promotion in iommu_mmio_write(), dbg_mmio_offset is int

and iommu->mmio_phys_end is u64

if (dbg_mmio_offset > iommu->mmio_phys_end - sizeof(u64))

return -EINVAL;

3. The show handlers would currently catch the negative number and

refuse to perform the read.

Replace kstrtou32_from_user() with kstrtos32_from_user() to parse the

input, and check for negative values to explicitly prevent out-of-bounds

memory accesses directly in iommu_mmio_write() and

iommu_capability_write().