[RFC 4/7] mm/kasan, mm/vmalloc: Respect GFP flags in kasan_populate_vmalloc()

Uladzislau Rezki (Sony)
2025-07-04T15:25:54Z

The function kasan_populate_vmalloc() internally allocates a page using
a hardcoded GFP_KERNEL flag. This is not safe in contexts where non-blocking
allocation flags are required, such as GFP_ATOMIC or GFP_NOWAIT, for example
during atomic vmalloc paths.

This patch modifies kasan_populate_vmalloc() and its helpers to accept a
gfp_mask argument to use it for a page allocation. It allows the caller to
specify the correct allocation context.

Also, when non-blocking flags are used, memalloc_noreclaim_save/restore()
is used around apply_to_page_range() to suppress potential reclaim behavior
that may otherwise violate atomic constraints.

Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
include/linux/kasan.h | 6 +++---
mm/kasan/shadow.c | 22 +++++++++++++++-------
mm/vmalloc.c | 4 ++--
3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 890011071f2b..fe5ce9215821 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -562,7 +562,7 @@ static inline void kasan_init_hw_tags(void) { }
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)

void kasan_populate_early_vm_area_shadow(void *start, unsigned long size);
-int kasan_populate_vmalloc(unsigned long addr, unsigned long size);
+int kasan_populate_vmalloc(unsigned long addr, unsigned long size, gfp_t gfp_mask);
void kasan_release_vmalloc(unsigned long start, unsigned long end,
unsigned long free_region_start,
unsigned long free_region_end,
@@ -574,7 +574,7 @@ static inline void kasan_populate_early_vm_area_shadow(void *start,
unsigned long size)
{ }
static inline int kasan_populate_vmalloc(unsigned long start,
- unsigned long size)
+ unsigned long size, gfp_t gfp_mask)
{
return 0;
}
@@ -610,7 +610,7 @@ static __always_inline void kasan_poison_vmalloc(const void *start,
static inline void kasan_populate_early_vm_area_shadow(void *start,
unsigned long size) { }
static inline int kasan_populate_vmalloc(unsigned long start,
- unsigned long size)
+ unsigned long size, gfp_t gfp_mask)
{
return 0;
}
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index d2c70cd2afb1..5edfc1f6b53e 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -335,13 +335,13 @@ static void ___free_pages_bulk(struct page **pages, int nr_pages)
}
}

-static int ___alloc_pages_bulk(struct page **pages, int nr_pages)
+static int ___alloc_pages_bulk(struct page **pages, int nr_pages, gfp_t gfp_mask)
{
unsigned long nr_populated, nr_total = nr_pages;
struct page **page_array = pages;

while (nr_pages) {
- nr_populated = alloc_pages_bulk(GFP_KERNEL, nr_pages, pages);
+ nr_populated = alloc_pages_bulk(gfp_mask, nr_pages, pages);
if (!nr_populated) {
___free_pages_bulk(page_array, nr_total - nr_pages);
return -ENOMEM;
@@ -353,25 +353,33 @@ static int ___alloc_pages_bulk(struct page **pages, int nr_pages)
return 0;
}

-static int __kasan_populate_vmalloc(unsigned long start, unsigned long end)
+static int __kasan_populate_vmalloc(unsigned long start, unsigned long end, gfp_t gfp_mask)
{
unsigned long nr_pages, nr_total = PFN_UP(end - start);
+ bool noblock = !gfpflags_allow_blocking(gfp_mask);
struct vmalloc_populate_data data;
+ unsigned int flags;
int ret = 0;

- data.pages = (struct page **)__get_free_page(GFP_KERNEL | __GFP_ZERO);
+ data.pages = (struct page **)__get_free_page(gfp_mask | __GFP_ZERO);
if (!data.pages)
return -ENOMEM;

while (nr_total) {
nr_pages = min(nr_total, PAGE_SIZE / sizeof(data.pages[0]));
- ret = ___alloc_pages_bulk(data.pages, nr_pages);
+ ret = ___alloc_pages_bulk(data.pages, nr_pages, gfp_mask);
if (ret)
break;

data.start = start;
+ if (noblock)
+ flags = memalloc_noreclaim_save();
+
ret = apply_to_page_range(&init_mm, start, nr_pages * PAGE_SIZE,
kasan_populate_vmalloc_pte, &data);
+ if (noblock)
+ memalloc_noreclaim_restore(flags);
+
___free_pages_bulk(data.pages, nr_pages);
if (ret)
break;
@@ -385,7 +393,7 @@ static int __kasan_populate_vmalloc(unsigned long start, unsigned long end)
return ret;
}

-int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
+int kasan_populate_vmalloc(unsigned long addr, unsigned long size, gfp_t gfp_mask)
{
unsigned long shadow_start, shadow_end;
int ret;
@@ -414,7 +422,7 @@ int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
shadow_start = PAGE_ALIGN_DOWN(shadow_start);
shadow_end = PAGE_ALIGN(shadow_end);

- ret = __kasan_populate_vmalloc(shadow_start, shadow_end);
+ ret = __kasan_populate_vmalloc(shadow_start, shadow_end, gfp_mask);
if (ret)
return ret;

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 25d09f753239..5bac15b09b03 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2091,7 +2091,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
BUG_ON(va->va_start < vstart);
BUG_ON(va->va_end > vend);

- ret = kasan_populate_vmalloc(addr, size);
+ ret = kasan_populate_vmalloc(addr, size, gfp_mask);
if (ret) {
free_vmap_area(va);
return ERR_PTR(ret);
@@ -4832,7 +4832,7 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,

/* populate the kasan shadow space */
for (area = 0; area < nr_vms; area++) {
- if (kasan_populate_vmalloc(vas[area]->va_start, sizes[area]))
+ if (kasan_populate_vmalloc(vas[area]->va_start, sizes[area], GFP_KERNEL))
goto err_free_shadow;
}

--
2.39.5