From 8dfd3d8d74435344ee8dc9237596959c8b2a6cbe Mon Sep 17 00:00:00 2001 From: Eder Zulian Date: Fri, 10 Apr 2026 14:55:50 +0200 Subject: [PATCH] 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(). Signed-off-by: Eder Zulian Fixes: 7a4ee419e8c1 ("iommu/amd: Add debugfs support to dump IOMMU MMIO registers") Cc: stable@vger.kernel.org Signed-off-by: Joerg Roedel --- drivers/iommu/amd/debugfs.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/drivers/iommu/amd/debugfs.c b/drivers/iommu/amd/debugfs.c index 4e66473d7cea..4c53b6361314 100644 --- a/drivers/iommu/amd/debugfs.c +++ b/drivers/iommu/amd/debugfs.c @@ -31,11 +31,12 @@ static ssize_t iommu_mmio_write(struct file *filp, const char __user *ubuf, if (cnt > OFS_IN_SZ) return -EINVAL; - ret = kstrtou32_from_user(ubuf, cnt, 0, &dbg_mmio_offset); + ret = kstrtos32_from_user(ubuf, cnt, 0, &dbg_mmio_offset); if (ret) return ret; - if (dbg_mmio_offset > iommu->mmio_phys_end - sizeof(u64)) + if (dbg_mmio_offset < 0 || dbg_mmio_offset > + iommu->mmio_phys_end - sizeof(u64)) return -EINVAL; iommu->dbg_mmio_offset = dbg_mmio_offset; @@ -71,12 +72,12 @@ static ssize_t iommu_capability_write(struct file *filp, const char __user *ubuf if (cnt > OFS_IN_SZ) return -EINVAL; - ret = kstrtou32_from_user(ubuf, cnt, 0, &dbg_cap_offset); + ret = kstrtos32_from_user(ubuf, cnt, 0, &dbg_cap_offset); if (ret) return ret; /* Capability register at offset 0x14 is the last IOMMU capability register. */ - if (dbg_cap_offset > 0x14) + if (dbg_cap_offset < 0 || dbg_cap_offset > 0x14) return -EINVAL; iommu->dbg_cap_offset = dbg_cap_offset;