Subject: Re: [PATCH v8 1/5] kasan: support backing vmalloc space with real shadow memory

From: Uladzislau Rezki <[email-masked]>
Date: Tue, 1 Oct 2019 12:17:07 +0200

Hello, Daniel.

> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a3c70e275f4e..9fb7a16f42ae 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -690,8 +690,19 @@ merge_or_add_vmap_area(struct vmap_area *va,
>  	struct list_head *next;
>  	struct rb_node **link;
>  	struct rb_node *parent;
> +	unsigned long orig_start, orig_end;
Shouldn't that be wrapped around #ifdef CONFIG_KASAN_VMALLOC?

>  	bool merged = false;
>  
> +	/*
> +	 * To manage KASAN vmalloc memory usage, we use this opportunity to
> +	 * clean up the shadow memory allocated to back this allocation.
> +	 * Because a vmalloc shadow page covers several pages, the start or end
> +	 * of an allocation might not align with a shadow page. Use the merging
> +	 * opportunities to try to extend the region we can release.
> +	 */
> +	orig_start = va->va_start;
> +	orig_end = va->va_end;
> +
The same.

>  	/*
>  	 * Find a place in the tree where VA potentially will be
>  	 * inserted, unless it is merged with its sibling/siblings.
> @@ -741,6 +752,10 @@ merge_or_add_vmap_area(struct vmap_area *va,
>  		if (sibling->va_end == va->va_start) {
>  			sibling->va_end = va->va_end;
>  
> +			kasan_release_vmalloc(orig_start, orig_end,
> +					      sibling->va_start,
> +					      sibling->va_end);
> +
The same.

>  			/* Check and update the tree if needed. */
>  			augment_tree_propagate_from(sibling);
>  
> @@ -754,6 +769,8 @@ merge_or_add_vmap_area(struct vmap_area *va,
>  	}
>  
>  insert:
> +	kasan_release_vmalloc(orig_start, orig_end, va->va_start, va->va_end);
> +
The same + all further changes in this file.
>  	if (!merged) {
>  		link_va(va, root, parent, link, head);
>  		augment_tree_propagate_from(va);
> @@ -2068,6 +2085,22 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
>  
>  	setup_vmalloc_vm(area, va, flags, caller);
>  
> +	/*
> +	 * 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;
> +		}
> +	}
> +
>  	return area;
>  }
>  
> @@ -2245,6 +2278,9 @@ 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);
> +
>  	vm_remove_mappings(area, deallocate_pages);
>  
>  	if (deallocate_pages) {
> @@ -2497,6 +2533,9 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
>  	if (!addr)
>  		return NULL;
>  
> +	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.
> @@ -3351,10 +3390,14 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>  	spin_unlock(&vmap_area_lock);
>  
>  	/* insert all vm's */
> -	for (area = 0; area < nr_vms; area++)
> +	for (area = 0; area < nr_vms; area++) {
>  		setup_vmalloc_vm(vms[area], vas[area], VM_ALLOC,
>  				 pcpu_get_vm_areas);
>  
> +		/* assume success here */
> +		kasan_populate_vmalloc(sizes[area], vms[area]);
> +	}
> +
>  	kfree(vas);
>  	return vms;
>  

--
Vlad Rezki