Mark Rutland <mark.rutland@xxxxxxx> writes: > On Tue, Oct 01, 2019 at 04:58:30PM +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 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> >> Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx> >> [Mark: rework shadow allocation] >> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> > > Sorry to point this out so late, but your S-o-B should come last in the > chain per Documentation/process/submitting-patches.rst. Judging by the > rest of that, I think you want something like: > > 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> > > ... leaving yourself as the Author in the headers. no worries, I wasn't really sure how best to arrange them, so thanks for clarifying! > > Sorry to have made that more complicated! > > [...] > >> +static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr, >> + void *unused) >> +{ >> + unsigned long page; >> + >> + page = (unsigned long)__va(pte_pfn(*ptep) << PAGE_SHIFT); >> + >> + spin_lock(&init_mm.page_table_lock); >> + >> + if (likely(!pte_none(*ptep))) { >> + pte_clear(&init_mm, addr, ptep); >> + free_page(page); >> + } > > There should be TLB maintenance between clearing the PTE and freeing the > page here. Fixed for v9. Regards, Daniel > > Thanks, > Mark.
