FAILED: patch "[PATCH] iommu/amd: Remove latent out-of-bounds access in IOMMU" failed to apply to 6.18-stable tree

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 8dfd3d8d74435344ee8dc9237596959c8b2a6cbe
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026052055-satirical-mousy-05cf@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8dfd3d8d74435344ee8dc9237596959c8b2a6cbe Mon Sep 17 00:00:00 2001
From: Eder Zulian <[email protected]>
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().

index 4e66473d7cea..4c53b6361314 100644
@@ -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;

In iommu_mmio_write() and iommu_capability_write(), iommu->dbg_mmio_offset and iommu->dbg_cap_offset are 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(), iommu->dbg_mmio_offset is int and iommu->mmio_phys_end is u64

if (iommu->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().

---
 drivers/iommu/amd/debugfs.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

index 20b04996441d..bb0c8552bc0f 100644
@@ -33,11 +33,12 @@ 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, &iommu->dbg_mmio_offset);
+	ret = kstrtos32_from_user(ubuf, cnt, 0, &iommu->dbg_mmio_offset);
 	if (ret)
 		return ret;
 
-	if (iommu->dbg_mmio_offset > iommu->mmio_phys_end - sizeof(u64)) {
+	if (iommu->dbg_mmio_offset < 0 || iommu->dbg_mmio_offset >
+			iommu->mmio_phys_end - sizeof(u64)) {
 		iommu->dbg_mmio_offset = -1;
 		return  -EINVAL;
 	}

@@ -74,12 +75,12 @@ 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, &iommu->dbg_cap_offset);
+	ret = kstrtos32_from_user(ubuf, cnt, 0, &iommu->dbg_cap_offset);
 	if (ret)
 		return ret;
 
 	/* Capability register at offset 0x14 is the last IOMMU capability register. */
-	if (iommu->dbg_cap_offset > 0x14) {
+	if (iommu->dbg_cap_offset < 0 || iommu->dbg_cap_offset > 0x14) {
 		iommu->dbg_cap_offset = -1;
 		return -EINVAL;
 	}

2.54.0