[PATCH v2] kasan: fix crashes on access to memory mapped by vm_map_ram()

Andrey Ryabinin
2019-12-05T10:00:19Z

With CONFIG_KASAN_VMALLOC=y any use of memory obtained via vm_map_ram()
will crash because there is no shadow backing that memory.

Instead of sprinkling additional kasan_populate_vmalloc() calls all over
the vmalloc code, move it into alloc_vmap_area(). This will fix
vm_map_ram() and simplify the code a bit.

Fixes: 3c5c3cfb9ef4 ("kasan: support backing vmalloc space with real shadow memory")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---

Changes since v1:
- Fix error path in alloc_vmap_area.
- Remove wrong Reported-by: syzbot (The issue reported by bot is a different one)

include/linux/kasan.h | 15 +++++---
mm/kasan/common.c | 27 +++++++++-----
mm/vmalloc.c | 85 ++++++++++++++++++++-----------------------
3 files changed, 67 insertions(+), 60 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 4f404c565db1..e18fe54969e9 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -205,20 +205,23 @@ static inline void *kasan_reset_tag(const void *addr)
#endif /* CONFIG_KASAN_SW_TAGS */

#ifdef CONFIG_KASAN_VMALLOC
-int kasan_populate_vmalloc(unsigned long requested_size,
- struct vm_struct *area);
-void kasan_poison_vmalloc(void *start, unsigned long size);
+int kasan_populate_vmalloc(unsigned long addr, unsigned long size);
+void kasan_poison_vmalloc(const void *start, unsigned long size);
+void kasan_unpoison_vmalloc(const void *start, unsigned long size);
void kasan_release_vmalloc(unsigned long start, unsigned long end,
unsigned long free_region_start,
unsigned long free_region_end);
#else
-static inline int kasan_populate_vmalloc(unsigned long requested_size,
- struct vm_struct *area)
+static inline int kasan_populate_vmalloc(unsigned long start,
+ unsigned long size)
{
return 0;
}

-static inline void kasan_poison_vmalloc(void *start, unsigned long size) {}
+static inline void kasan_poison_vmalloc(const void *start, unsigned long size)
+{ }
+static inline void kasan_unpoison_vmalloc(const void *start, unsigned long size)
+{ }
static inline void kasan_release_vmalloc(unsigned long start,
unsigned long end,
unsigned long free_region_start,
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index df3371d5c572..a1e6273be8c3 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -777,15 +777,17 @@ static int kasan_populate_vmalloc_pte(pte_t *ptep, unsigned long addr,
return 0;
}

-int kasan_populate_vmalloc(unsigned long requested_size, struct vm_struct *area)
+int kasan_populate_vmalloc(unsigned long addr, unsigned long size)
{
unsigned long shadow_start, shadow_end;
int ret;

- shadow_start = (unsigned long)kasan_mem_to_shadow(area->addr);
+ if (!is_vmalloc_or_module_addr((void *)addr))
+ return 0;
+
+ shadow_start = (unsigned long)kasan_mem_to_shadow((void *)addr);
shadow_start = ALIGN_DOWN(shadow_start, PAGE_SIZE);
- shadow_end = (unsigned long)kasan_mem_to_shadow(area->addr +
- area->size);
+ shadow_end = (unsigned long)kasan_mem_to_shadow((void *)addr + size);
shadow_end = ALIGN(shadow_end, PAGE_SIZE);

ret = apply_to_page_range(&init_mm, shadow_start,
@@ -796,10 +798,6 @@ int kasan_populate_vmalloc(unsigned long requested_size, struct vm_struct *area)

flush_cache_vmap(shadow_start, shadow_end);

- kasan_unpoison_shadow(area->addr, requested_size);
-
- area->flags |= VM_KASAN;
-
/*
* We need to be careful about inter-cpu effects here. Consider:
*
@@ -842,12 +840,23 @@ int kasan_populate_vmalloc(unsigned long requested_size, struct vm_struct *area)
* Poison the shadow for a vmalloc region. Called as part of the
* freeing process at the time the region is freed.
*/
-void kasan_poison_vmalloc(void *start, unsigned long size)
+void kasan_poison_vmalloc(const void *start, unsigned long size)
{
+ if (!is_vmalloc_or_module_addr(start))
+ return;
+
size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
kasan_poison_shadow(start, size, KASAN_VMALLOC_INVALID);
}

+void kasan_unpoison_vmalloc(const void *start, unsigned long size)
+{
+ if (!is_vmalloc_or_module_addr(start))
+ return;
+
+ kasan_unpoison_shadow(start, size);
+}
+
static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
void *unused)
{
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 4d3b3d60d893..6e865cea846c 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1061,6 +1061,26 @@ __alloc_vmap_area(unsigned long size, unsigned long align,
return nva_start_addr;
}

+/*
+ * Free a region of KVA allocated by alloc_vmap_area
+ */
+static void free_vmap_area(struct vmap_area *va)
+{
+ /*
+ * Remove from the busy tree/list.
+ */
+ spin_lock(&vmap_area_lock);
+ unlink_va(va, &vmap_area_root);
+ spin_unlock(&vmap_area_lock);
+
+ /*
+ * Insert/Merge it back to the free tree/list.
+ */
+ spin_lock(&free_vmap_area_lock);
+ merge_or_add_vmap_area(va, &free_vmap_area_root, &free_vmap_area_list);
+ spin_unlock(&free_vmap_area_lock);
+}
+
/*
* Allocate a region of KVA of the specified size and alignment, within the
* vstart and vend.
@@ -1073,6 +1093,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
struct vmap_area *va, *pva;
unsigned long addr;
int purged = 0;
+ int ret;

BUG_ON(!size);
BUG_ON(offset_in_page(size));
@@ -1139,6 +1160,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
va->va_end = addr + size;
va->vm = NULL;

+
spin_lock(&vmap_area_lock);
insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
spin_unlock(&vmap_area_lock);
@@ -1147,6 +1169,12 @@ 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);
+ if (ret) {
+ free_vmap_area(va);
+ return ERR_PTR(ret);
+ }
+
return va;

overflow:
@@ -1185,26 +1213,6 @@ int unregister_vmap_purge_notifier(struct notifier_block *nb)
}
EXPORT_SYMBOL_GPL(unregister_vmap_purge_notifier);

-/*
- * Free a region of KVA allocated by alloc_vmap_area
- */
-static void free_vmap_area(struct vmap_area *va)
-{
- /*
- * Remove from the busy tree/list.
- */
- spin_lock(&vmap_area_lock);
- unlink_va(va, &vmap_area_root);
- spin_unlock(&vmap_area_lock);
-
- /*
- * Insert/Merge it back to the free tree/list.
- */
- spin_lock(&free_vmap_area_lock);
- merge_or_add_vmap_area(va, &free_vmap_area_root, &free_vmap_area_list);
- spin_unlock(&free_vmap_area_lock);
-}
-
/*
* Clear the pagetable entries of a given vmap_area
*/
@@ -1771,6 +1779,8 @@ void vm_unmap_ram(const void *mem, unsigned int count)
BUG_ON(addr > VMALLOC_END);
BUG_ON(!PAGE_ALIGNED(addr));

+ kasan_poison_vmalloc(mem, size);
+
if (likely(count <= VMAP_MAX_ALLOC)) {
debug_check_no_locks_freed(mem, size);
vb_free(mem, size);
@@ -1821,6 +1831,9 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node, pgprot_t pro
addr = va->va_start;
mem = (void *)addr;
}
+
+ kasan_unpoison_vmalloc(mem, size);
+
if (vmap_page_range(addr, addr + size, prot, pages) < 0) {
vm_unmap_ram(mem, count);
return NULL;
@@ -2075,6 +2088,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
{
struct vmap_area *va;
struct vm_struct *area;
+ unsigned long requested_size = size;

BUG_ON(in_interrupt());
size = PAGE_ALIGN(size);
@@ -2098,23 +2112,9 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
return NULL;
}

- setup_vmalloc_vm(area, va, flags, caller);
+ kasan_unpoison_vmalloc((void *)va->va_start, requested_size);

- /*
- * For KASAN, if we are in vmalloc space, we need to cover the shadow
- * area with real memory. If we come here through VM_ALLOC, this is
- * done by a higher level function that has access to the true size,
- * which might not be a full page.
- *
- * We assume module space comes via VM_ALLOC path.
- */
- if (is_vmalloc_addr(area->addr) && !(area->flags & VM_ALLOC)) {
- if (kasan_populate_vmalloc(area->size, area)) {
- unmap_vmap_area(va);
- kfree(area);
- return NULL;
- }
- }
+ setup_vmalloc_vm(area, va, flags, caller);

return area;
}
@@ -2293,8 +2293,7 @@ static void __vunmap(const void *addr, int deallocate_pages)
debug_check_no_locks_freed(area->addr, get_vm_area_size(area));
debug_check_no_obj_freed(area->addr, get_vm_area_size(area));

- if (area->flags & VM_KASAN)
- kasan_poison_vmalloc(area->addr, area->size);
+ kasan_poison_vmalloc(area->addr, area->size);

vm_remove_mappings(area, deallocate_pages);

@@ -2539,7 +2538,7 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
if (!size || (size >> PAGE_SHIFT) > totalram_pages())
goto fail;

- area = __get_vm_area_node(size, align, VM_ALLOC | VM_UNINITIALIZED |
+ area = __get_vm_area_node(real_size, align, VM_ALLOC | VM_UNINITIALIZED |
vm_flags, start, end, node, gfp_mask, caller);
if (!area)
goto fail;
@@ -2548,11 +2547,6 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
if (!addr)
return NULL;

- if (is_vmalloc_or_module_addr(area->addr)) {
- if (kasan_populate_vmalloc(real_size, area))
- return NULL;
- }
-
/*
* In this function, newly allocated vm_struct has VM_UNINITIALIZED
* flag. It means that vm_struct is not fully initialized.
@@ -3437,7 +3431,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
/* populate the shadow space outside of the lock */
for (area = 0; area < nr_vms; area++) {
/* assume success here */
- kasan_populate_vmalloc(sizes[area], vms[area]);
+ kasan_populate_vmalloc(vas[area]->va_start, sizes[area]);
+ kasan_unpoison_vmalloc((void *)vms[area]->addr, sizes[area]);
}

kfree(vas);
--
2.23.0