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

Uladzislau Rezki
2019-12-06T17:32:34Z

On Thu, Dec 05, 2019 at 12:59:42PM +0300, Andrey Ryabinin wrote:
> 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
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

--
Vlad Rezki
>