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  3. [PATCH v5 0/4] iommu: Add IOMMU_DEBUG_PAGEALLOC sanitizer
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[PATCH v5 4/4] iommu: debug-pagealloc: Check mapped/unmapped kernel memory

Mostafa Saleh posted 4 patches 1 month ago
[PATCH v5 4/4] iommu: debug-pagealloc: Check mapped/unmapped kernel memory
Posted by Mostafa Saleh 1 month ago 
Now, as the page_ext holds count of IOMMU mappings, we can use it to
assert that any page allocated/freed is indeed not in the IOMMU.

The sanitizer doesn’t protect against mapping/unmapping during this
period. However, that’s less harmful as the page is not used by the
kernel.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mostafa Saleh <smostafa@google.com>
---
 drivers/iommu/iommu-debug-pagealloc.c | 23 +++++++++++++++++++++++
 include/linux/iommu-debug-pagealloc.h | 14 ++++++++++++++
 include/linux/mm.h                    |  5 +++++
 3 files changed, 42 insertions(+)

diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c
index 86ccb310a4a8..5353417e64f9 100644
--- a/drivers/iommu/iommu-debug-pagealloc.c
+++ b/drivers/iommu/iommu-debug-pagealloc.c
@@ -9,6 +9,7 @@
 #include <linux/iommu-debug-pagealloc.h>
 #include <linux/kernel.h>
 #include <linux/page_ext.h>
+#include <linux/page_owner.h>
 
 #include "iommu-priv.h"
 
@@ -73,6 +74,28 @@ static size_t iommu_debug_page_size(struct iommu_domain *domain)
 	return 1UL << __ffs(domain->pgsize_bitmap);
 }
 
+static bool iommu_debug_page_count(const struct page *page)
+{
+	unsigned int ref;
+	struct page_ext *page_ext = page_ext_get(page);
+	struct iommu_debug_metadata *d = get_iommu_data(page_ext);
+
+	ref = atomic_read(&d->ref);
+	page_ext_put(page_ext);
+	return ref != 0;
+}
+
+void __iommu_debug_check_unmapped(const struct page *page, int numpages)
+{
+	while (numpages--) {
+		if (WARN_ON(iommu_debug_page_count(page))) {
+			pr_warn("iommu: Detected page leak!\n");
+			dump_page_owner(page);
+		}
+		page++;
+	}
+}
+
 void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t size)
 {
 	size_t off, end;
diff --git a/include/linux/iommu-debug-pagealloc.h b/include/linux/iommu-debug-pagealloc.h
index a439d6815ca1..46c3c1f70150 100644
--- a/include/linux/iommu-debug-pagealloc.h
+++ b/include/linux/iommu-debug-pagealloc.h
@@ -13,6 +13,20 @@ DECLARE_STATIC_KEY_FALSE(iommu_debug_initialized);
 
 extern struct page_ext_operations page_iommu_debug_ops;
 
+void __iommu_debug_check_unmapped(const struct page *page, int numpages);
+
+static inline void iommu_debug_check_unmapped(const struct page *page, int numpages)
+{
+	if (static_branch_unlikely(&iommu_debug_initialized))
+		__iommu_debug_check_unmapped(page, numpages);
+}
+
+#else
+static inline void iommu_debug_check_unmapped(const struct page *page,
+					      int numpages)
+{
+}
+
 #endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */
 
 #endif /* __LINUX_IOMMU_DEBUG_PAGEALLOC_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6f959d8ca4b4..32205d2a24b2 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -36,6 +36,7 @@
 #include <linux/rcuwait.h>
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
+#include <linux/iommu-debug-pagealloc.h>
 
 struct mempolicy;
 struct anon_vma;
@@ -4133,12 +4134,16 @@ extern void __kernel_map_pages(struct page *page, int numpages, int enable);
 #ifdef CONFIG_DEBUG_PAGEALLOC
 static inline void debug_pagealloc_map_pages(struct page *page, int numpages)
 {
+	iommu_debug_check_unmapped(page, numpages);
+
 	if (debug_pagealloc_enabled_static())
 		__kernel_map_pages(page, numpages, 1);
 }
 
 static inline void debug_pagealloc_unmap_pages(struct page *page, int numpages)
 {
+	iommu_debug_check_unmapped(page, numpages);
+
 	if (debug_pagealloc_enabled_static())
 		__kernel_map_pages(page, numpages, 0);
 }
-- 
2.52.0.351.gbe84eed79e-goog
Re: [PATCH v5 4/4] iommu: debug-pagealloc: Check mapped/unmapped kernel memory
Posted by Samiullah Khawaja 1 month ago 
On Tue, Jan 6, 2026 at 8:22 AM Mostafa Saleh <smostafa@google.com> wrote:
>
> Now, as the page_ext holds count of IOMMU mappings, we can use it to
> assert that any page allocated/freed is indeed not in the IOMMU.
>
> The sanitizer doesn’t protect against mapping/unmapping during this
> period. However, that’s less harmful as the page is not used by the
> kernel.
>
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Mostafa Saleh <smostafa@google.com>
> ---
>  drivers/iommu/iommu-debug-pagealloc.c | 23 +++++++++++++++++++++++
>  include/linux/iommu-debug-pagealloc.h | 14 ++++++++++++++
>  include/linux/mm.h                    |  5 +++++
>  3 files changed, 42 insertions(+)
>
> diff --git a/drivers/iommu/iommu-debug-pagealloc.c b/drivers/iommu/iommu-debug-pagealloc.c
> index 86ccb310a4a8..5353417e64f9 100644
> --- a/drivers/iommu/iommu-debug-pagealloc.c
> +++ b/drivers/iommu/iommu-debug-pagealloc.c
> @@ -9,6 +9,7 @@
>  #include <linux/iommu-debug-pagealloc.h>
>  #include <linux/kernel.h>
>  #include <linux/page_ext.h>
> +#include <linux/page_owner.h>
>
>  #include "iommu-priv.h"
>
> @@ -73,6 +74,28 @@ static size_t iommu_debug_page_size(struct iommu_domain *domain)
>         return 1UL << __ffs(domain->pgsize_bitmap);
>  }
>
> +static bool iommu_debug_page_count(const struct page *page)
> +{
> +       unsigned int ref;
> +       struct page_ext *page_ext = page_ext_get(page);
> +       struct iommu_debug_metadata *d = get_iommu_data(page_ext);
> +
> +       ref = atomic_read(&d->ref);
> +       page_ext_put(page_ext);
> +       return ref != 0;
> +}
> +
> +void __iommu_debug_check_unmapped(const struct page *page, int numpages)
> +{
> +       while (numpages--) {
> +               if (WARN_ON(iommu_debug_page_count(page))) {
> +                       pr_warn("iommu: Detected page leak!\n");
> +                       dump_page_owner(page);
> +               }
> +               page++;
> +       }
> +}
> +
>  void __iommu_debug_map(struct iommu_domain *domain, phys_addr_t phys, size_t size)
>  {
>         size_t off, end;
> diff --git a/include/linux/iommu-debug-pagealloc.h b/include/linux/iommu-debug-pagealloc.h
> index a439d6815ca1..46c3c1f70150 100644
> --- a/include/linux/iommu-debug-pagealloc.h
> +++ b/include/linux/iommu-debug-pagealloc.h
> @@ -13,6 +13,20 @@ DECLARE_STATIC_KEY_FALSE(iommu_debug_initialized);
>
>  extern struct page_ext_operations page_iommu_debug_ops;
>
> +void __iommu_debug_check_unmapped(const struct page *page, int numpages);
> +
> +static inline void iommu_debug_check_unmapped(const struct page *page, int numpages)
> +{
> +       if (static_branch_unlikely(&iommu_debug_initialized))
> +               __iommu_debug_check_unmapped(page, numpages);
> +}
> +
> +#else
> +static inline void iommu_debug_check_unmapped(const struct page *page,
> +                                             int numpages)
> +{
> +}
> +
>  #endif /* CONFIG_IOMMU_DEBUG_PAGEALLOC */
>
>  #endif /* __LINUX_IOMMU_DEBUG_PAGEALLOC_H */
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6f959d8ca4b4..32205d2a24b2 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -36,6 +36,7 @@
>  #include <linux/rcuwait.h>
>  #include <linux/bitmap.h>
>  #include <linux/bitops.h>
> +#include <linux/iommu-debug-pagealloc.h>
>
>  struct mempolicy;
>  struct anon_vma;
> @@ -4133,12 +4134,16 @@ extern void __kernel_map_pages(struct page *page, int numpages, int enable);
>  #ifdef CONFIG_DEBUG_PAGEALLOC
>  static inline void debug_pagealloc_map_pages(struct page *page, int numpages)
>  {
> +       iommu_debug_check_unmapped(page, numpages);
> +
>         if (debug_pagealloc_enabled_static())
>                 __kernel_map_pages(page, numpages, 1);
>  }
>
>  static inline void debug_pagealloc_unmap_pages(struct page *page, int numpages)
>  {
> +       iommu_debug_check_unmapped(page, numpages);
> +
>         if (debug_pagealloc_enabled_static())
>                 __kernel_map_pages(page, numpages, 0);
>  }
> --
> 2.52.0.351.gbe84eed79e-goog
>
>

Reviewed-by: Samiullah Khawaja <skhawaja@google.com>

Patchew 2.1-devel-b67e4c2

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