On Wed, Jul 31, 2019 at 05:15:48PM +1000, 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 the first time a mapping in vmalloc space uses a > particular page of the shadow region. Keep this page around > regardless of whether the mapping is later freed - in the mean time > the page could have become shared by another vmalloc mapping. > > This can in theory lead to unbounded memory growth, but the vmalloc > allocator is pretty good at reusing addresses, so the practical memory > usage grows at first but then stays fairly stable. > > This requires architecture support to actually use: arches must stop > mapping the read-only zero page over portion of the shadow region that > covers the vmalloc space and instead leave it unmapped. > > This allows KASAN with VMAP_STACK, and will be needed 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 > Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> > > --- Acked-by: Vasily Gorbik <gor@xxxxxxxxxxxxx> I've added s390 specific kasan init part and the whole thing looks good! Unfortunately I also had to make additional changes in s390 code, so s390 part would go later through s390 tree. But looking forward seeing your patch series upstream.
