Re: [PATCH] vfio: fix VFIO_IOMMU_UNMAP_DMA when end of range would overflow u64

Alex Mastro
2025-10-07T04:24:49Z

On Mon, Oct 06, 2025 at 09:23:56PM -0400, Alejandro Jimenez wrote:
> If going this way, we'd also have to deny the MAP requests. Right now we

Agree.

> > I have doubts that anyone actually relies on MAP_DMA-ing such
> > end-of-u64-mappings in practice, so perhaps it's OK?
> >
>
> The AMD IOMMU supports a 64-bit IOVA, so when using the AMD vIOMMU with DMA
> remapping enabled + VF passthrough + a Linux guest with iommu.forcedac=1 we
> hit this issue since the driver (mlx5) starts requesting mappings for IOVAs
> right at the top of the address space.

Interesting!

> The reason why I hadn't send it to the list yet is because I noticed the
> additional locations Jason mentioned earlier in the thread (e.g.
> vfio_find_dma(), vfio_iommu_replay()) and wanted to put together a
> reproducer that also triggered those paths.

I am not well equipped to test some of these paths, so if you have a recipe, I'd
be interested.

> I mentioned in the notes for the patch above why I chose a slightly more
> complex method than the '- 1' approach, since there is a chance that
> iova+size could also go beyond the end of the address space and actually
> wrap around.

I think certain invariants have broken if that is possible. The current checks
in the unmap path should prevent that (iova + size - 1 < iova).

1330 } else if (!size || size & (pgsize - 1) ||
1331 iova + size - 1 < iova || size > SIZE_MAX) {
1332 goto unlock;

> My goal was not to trust the inputs at all if possible. We could also use
> check_add_overflow() if we want to add explicit error reporting in
> vfio_iommu_type1 when an overflow is detected. i.e. catch bad callers that

I do like the explicitness of the check_* functions over the older style wrap
checks.

Below is my partially validated attempt at a more comprehensive fix if we were
to try and make end of address space mappings work, rather than blanking out
the last page.

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 08242d8ce2ca..66a25de35446 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -28,6 +28,7 @@
#include <linux/iommu.h>
#include <linux/module.h>
#include <linux/mm.h>
+#include <linux/overflow.h>
#include <linux/kthread.h>
#include <linux/rbtree.h>
#include <linux/sched/signal.h>
@@ -165,12 +166,14 @@ static struct vfio_dma *vfio_find_dma(struct vfio_iommu *iommu,
{
struct rb_node *node = iommu->dma_list.rb_node;

+ BUG_ON(size == 0);
+
while (node) {
struct vfio_dma *dma = rb_entry(node, struct vfio_dma, node);

- if (start + size <= dma->iova)
+ if (start + size - 1 < dma->iova)
node = node->rb_left;
- else if (start >= dma->iova + dma->size)
+ else if (start > dma->iova + dma->size - 1)
node = node->rb_right;
else
return dma;
@@ -186,10 +189,12 @@ static struct rb_node *vfio_find_dma_first_node(struct vfio_iommu *iommu,
struct rb_node *node = iommu->dma_list.rb_node;
struct vfio_dma *dma_res = NULL;

+ BUG_ON(size == 0);
+
while (node) {
struct vfio_dma *dma = rb_entry(node, struct vfio_dma, node);

- if (start < dma->iova + dma->size) {
+ if (start <= dma->iova + dma->size - 1) {
res = node;
dma_res = dma;
if (start >= dma->iova)
@@ -199,7 +204,7 @@ static struct rb_node *vfio_find_dma_first_node(struct vfio_iommu *iommu,
node = node->rb_right;
}
}
- if (res && size && dma_res->iova > start + size - 1)
+ if (res && dma_res->iova > start + size - 1)
res = NULL;
return res;
}
@@ -213,7 +218,7 @@ static void vfio_link_dma(struct vfio_iommu *iommu, struct vfio_dma *new)
parent = *link;
dma = rb_entry(parent, struct vfio_dma, node);

- if (new->iova + new->size <= dma->iova)
+ if (new->iova + new->size - 1 < dma->iova)
link = &(*link)->rb_left;
else
link = &(*link)->rb_right;
@@ -825,14 +830,24 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
unsigned long remote_vaddr;
struct vfio_dma *dma;
bool do_accounting;
+ u64 end, to_pin;

- if (!iommu || !pages)
+ if (!iommu || !pages || npage < 0)
return -EINVAL;

/* Supported for v2 version only */
if (!iommu->v2)
return -EACCES;

+ if (npage == 0)
+ return 0;
+
+ if (check_mul_overflow(npage, PAGE_SIZE, &to_pin))
+ return -EINVAL;
+
+ if (check_add_overflow(user_iova, to_pin - 1, &end))
+ return -EINVAL;
+
mutex_lock(&iommu->lock);

if (WARN_ONCE(iommu->vaddr_invalid_count,
@@ -997,7 +1012,7 @@ static long vfio_sync_unpin(struct vfio_dma *dma, struct vfio_domain *domain,
#define VFIO_IOMMU_TLB_SYNC_MAX 512

static size_t unmap_unpin_fast(struct vfio_domain *domain,
- struct vfio_dma *dma, dma_addr_t *iova,
+ struct vfio_dma *dma, dma_addr_t iova,
size_t len, phys_addr_t phys, long *unlocked,
struct list_head *unmapped_list,
int *unmapped_cnt,
@@ -1007,18 +1022,16 @@ static size_t unmap_unpin_fast(struct vfio_domain *domain,
struct vfio_regions *entry = kzalloc(sizeof(*entry), GFP_KERNEL);

if (entry) {
- unmapped = iommu_unmap_fast(domain->domain, *iova, len,
+ unmapped = iommu_unmap_fast(domain->domain, iova, len,
iotlb_gather);

if (!unmapped) {
kfree(entry);
} else {
- entry->iova = *iova;
+ entry->iova = iova;
entry->phys = phys;
entry->len = unmapped;
list_add_tail(&entry->list, unmapped_list);
-
- *iova += unmapped;
(*unmapped_cnt)++;
}
}
@@ -1037,18 +1050,17 @@ static size_t unmap_unpin_fast(struct vfio_domain *domain,
}

static size_t unmap_unpin_slow(struct vfio_domain *domain,
- struct vfio_dma *dma, dma_addr_t *iova,
+ struct vfio_dma *dma, dma_addr_t iova,
size_t len, phys_addr_t phys,
long *unlocked)
{
- size_t unmapped = iommu_unmap(domain->domain, *iova, len);
+ size_t unmapped = iommu_unmap(domain->domain, iova, len);

if (unmapped) {
- *unlocked += vfio_unpin_pages_remote(dma, *iova,
+ *unlocked += vfio_unpin_pages_remote(dma, iova,
phys >> PAGE_SHIFT,
unmapped >> PAGE_SHIFT,
false);
- *iova += unmapped;
cond_resched();
}
return unmapped;
@@ -1057,12 +1069,12 @@ static size_t unmap_unpin_slow(struct vfio_domain *domain,
static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
bool do_accounting)
{
- dma_addr_t iova = dma->iova, end = dma->iova + dma->size;
struct vfio_domain *domain, *d;
LIST_HEAD(unmapped_region_list);
struct iommu_iotlb_gather iotlb_gather;
int unmapped_region_cnt = 0;
long unlocked = 0;
+ size_t pos = 0;

if (!dma->size)
return 0;
@@ -1086,13 +1098,14 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
}

iommu_iotlb_gather_init(&iotlb_gather);
- while (iova < end) {
+ while (pos < dma->size) {
size_t unmapped, len;
phys_addr_t phys, next;
+ dma_addr_t iova = dma->iova + pos;

phys = iommu_iova_to_phys(domain->domain, iova);
if (WARN_ON(!phys)) {
- iova += PAGE_SIZE;
+ pos += PAGE_SIZE;
continue;
}

@@ -1101,7 +1114,7 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
* may require hardware cache flushing, try to find the
* largest contiguous physical memory chunk to unmap.
*/
- for (len = PAGE_SIZE; iova + len < end; len += PAGE_SIZE) {
+ for (len = PAGE_SIZE; len + pos < dma->size; len += PAGE_SIZE) {
next = iommu_iova_to_phys(domain->domain, iova + len);
if (next != phys + len)
break;
@@ -1111,16 +1124,18 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
* First, try to use fast unmap/unpin. In case of failure,
* switch to slow unmap/unpin path.
*/
- unmapped = unmap_unpin_fast(domain, dma, &iova, len, phys,
+ unmapped = unmap_unpin_fast(domain, dma, iova, len, phys,
&unlocked, &unmapped_region_list,
&unmapped_region_cnt,
&iotlb_gather);
if (!unmapped) {
- unmapped = unmap_unpin_slow(domain, dma, &iova, len,
+ unmapped = unmap_unpin_slow(domain, dma, iova, len,
phys, &unlocked);
if (WARN_ON(!unmapped))
break;
}
+
+ pos += unmapped;
}

dma->iommu_mapped = false;
@@ -1212,7 +1227,7 @@ static int update_user_bitmap(u64 __user *bitmap, struct vfio_iommu *iommu,
}

static int vfio_iova_dirty_bitmap(u64 __user *bitmap, struct vfio_iommu *iommu,
- dma_addr_t iova, size_t size, size_t pgsize)
+ dma_addr_t iova, u64 end, size_t pgsize)
{
struct vfio_dma *dma;
struct rb_node *n;
@@ -1229,8 +1244,8 @@ static int vfio_iova_dirty_bitmap(u64 __user *bitmap, struct vfio_iommu *iommu,
if (dma && dma->iova != iova)
return -EINVAL;

- dma = vfio_find_dma(iommu, iova + size - 1, 0);
- if (dma && dma->iova + dma->size != iova + size)
+ dma = vfio_find_dma(iommu, end, 1);
+ if (dma && dma->iova + dma->size - 1 != end)
return -EINVAL;

for (n = rb_first(&iommu->dma_list); n; n = rb_next(n)) {
@@ -1239,7 +1254,7 @@ static int vfio_iova_dirty_bitmap(u64 __user *bitmap, struct vfio_iommu *iommu,
if (dma->iova < iova)
continue;

- if (dma->iova > iova + size - 1)
+ if (dma->iova > end)
break;

ret = update_user_bitmap(bitmap, iommu, dma, iova, pgsize);
@@ -1305,6 +1320,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
unsigned long pgshift;
dma_addr_t iova = unmap->iova;
u64 size = unmap->size;
+ u64 unmap_end;
bool unmap_all = unmap->flags & VFIO_DMA_UNMAP_FLAG_ALL;
bool invalidate_vaddr = unmap->flags & VFIO_DMA_UNMAP_FLAG_VADDR;
struct rb_node *n, *first_n;
@@ -1327,11 +1343,13 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
if (iova || size)
goto unlock;
size = U64_MAX;
- } else if (!size || size & (pgsize - 1) ||
- iova + size - 1 < iova || size > SIZE_MAX) {
+ } else if (!size || size & (pgsize - 1) || size > SIZE_MAX) {
goto unlock;
}

+ if (check_add_overflow(iova, size - 1, &unmap_end))
+ goto unlock;
+
/* When dirty tracking is enabled, allow only min supported pgsize */
if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
(!iommu->dirty_page_tracking || (bitmap->pgsize != pgsize))) {
@@ -1376,8 +1394,8 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
if (dma && dma->iova != iova)
goto unlock;

- dma = vfio_find_dma(iommu, iova + size - 1, 0);
- if (dma && dma->iova + dma->size != iova + size)
+ dma = vfio_find_dma(iommu, unmap_end, 1);
+ if (dma && dma->iova + dma->size - 1 != unmap_end)
goto unlock;
}

@@ -1386,7 +1404,7 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,

while (n) {
dma = rb_entry(n, struct vfio_dma, node);
- if (dma->iova > iova + size - 1)
+ if (dma->iova > unmap_end)
break;

if (!iommu->v2 && iova > dma->iova)
@@ -1713,12 +1731,12 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,

for (; n; n = rb_next(n)) {
struct vfio_dma *dma;
- dma_addr_t iova;
+ size_t pos = 0;

dma = rb_entry(n, struct vfio_dma, node);
- iova = dma->iova;

- while (iova < dma->iova + dma->size) {
+ while (pos < dma->size) {
+ dma_addr_t iova = dma->iova + pos;
phys_addr_t phys;
size_t size;

@@ -1734,14 +1752,15 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
phys = iommu_iova_to_phys(d->domain, iova);

if (WARN_ON(!phys)) {
- iova += PAGE_SIZE;
+ pos += PAGE_SIZE;
continue;
}

+
size = PAGE_SIZE;
p = phys + size;
i = iova + size;
- while (i < dma->iova + dma->size &&
+ while (size + pos < dma->size &&
p == iommu_iova_to_phys(d->domain, i)) {
size += PAGE_SIZE;
p += PAGE_SIZE;
@@ -1782,7 +1801,7 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
goto unwind;
}

- iova += size;
+ pos += size;
}
}

@@ -1799,29 +1818,29 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
unwind:
for (; n; n = rb_prev(n)) {
struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
- dma_addr_t iova;
+ size_t pos = 0;

if (dma->iommu_mapped) {
iommu_unmap(domain->domain, dma->iova, dma->size);
continue;
}

- iova = dma->iova;
- while (iova < dma->iova + dma->size) {
+ while (pos < dma->size) {
+ dma_addr_t iova = dma->iova + pos;
phys_addr_t phys, p;
size_t size;
dma_addr_t i;

phys = iommu_iova_to_phys(domain->domain, iova);
if (!phys) {
- iova += PAGE_SIZE;
+ pos += PAGE_SIZE;
continue;
}

size = PAGE_SIZE;
p = phys + size;
i = iova + size;
- while (i < dma->iova + dma->size &&
+ while (pos + size < dma->size &&
p == iommu_iova_to_phys(domain->domain, i)) {
size += PAGE_SIZE;
p += PAGE_SIZE;
@@ -2908,6 +2927,7 @@ static int vfio_iommu_type1_dirty_pages(struct vfio_iommu *iommu,
unsigned long pgshift;
size_t data_size = dirty.argsz - minsz;
size_t iommu_pgsize;
+ u64 end;

if (!data_size || data_size < sizeof(range))
return -EINVAL;
@@ -2916,8 +2936,12 @@ static int vfio_iommu_type1_dirty_pages(struct vfio_iommu *iommu,
sizeof(range)))
return -EFAULT;

- if (range.iova + range.size < range.iova)
+ if (range.size == 0)
+ return 0;
+
+ if (check_add_overflow(range.iova, range.size - 1, &end))
return -EINVAL;
+
if (!access_ok((void __user *)range.bitmap.data,
range.bitmap.size))
return -EINVAL;
@@ -2949,7 +2973,7 @@ static int vfio_iommu_type1_dirty_pages(struct vfio_iommu *iommu,
if (iommu->dirty_page_tracking)
ret = vfio_iova_dirty_bitmap(range.bitmap.data,
iommu, range.iova,
- range.size,
+ end,
range.bitmap.pgsize);
else
ret = -EINVAL;