On 10/29/19 7:20 AM, Daniel Axtens wrote: > Hook into vmalloc and vmap, and dynamically allocate real shadow > memory to back the mappings. > > Most mappings in vmalloc space are small, requiring less than a full > page of shadow space. Allocating a full shadow page per mapping would > therefore be wasteful. Furthermore, to ensure that different mappings > use different shadow pages, mappings would have to be aligned to > KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE. > > Instead, share backing space across multiple mappings. Allocate a > backing page when a mapping in vmalloc space uses a particular page of > the shadow region. This page can be shared by other vmalloc mappings > later on. > > We hook in to the vmap infrastructure to lazily clean up unused shadow > memory. > > To avoid the difficulties around swapping mappings around, this code > expects that the part of the shadow region that covers the vmalloc > space will not be covered by the early shadow page, but will be left > unmapped. This will require changes in arch-specific code. > > This allows KASAN with VMAP_STACK, and may be helpful for architectures > that do not have a separate module space (e.g. powerpc64, which I am > currently working on). It also allows relaxing the module alignment > back to PAGE_SIZE. > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=202009 > Acked-by: Vasily Gorbik <gor@xxxxxxxxxxxxx> > Co-developed-by: Mark Rutland <mark.rutland@xxxxxxx> > Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> [shadow rework] > Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> Small nit bellow, otherwise looks fine: Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> > static __always_inline bool > @@ -1196,8 +1201,8 @@ static void free_vmap_area(struct vmap_area *va) > * 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); > + (void)merge_or_add_vmap_area(va, &free_vmap_area_root, > + &free_vmap_area_list); > spin_unlock(&free_vmap_area_lock); > } > .. > > @@ -3391,8 +3428,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets, > * and when pcpu_get_vm_areas() is success. > */ > while (area--) { > - merge_or_add_vmap_area(vas[area], > - &free_vmap_area_root, &free_vmap_area_list); > + (void)merge_or_add_vmap_area(vas[area], &free_vmap_area_root, I don't think these (void) casts are necessary. > + &free_vmap_area_list); > vas[area] = NULL; > } > >
