On Mon, Jul 03, 2017 at 12:13:51PM +0100, Ard Biesheuvel wrote: > Existing code that uses vmalloc_to_page() may assume that any address > for which is_vmalloc_addr() returns true may be passed into > vmalloc_to_page() to retrieve the associated struct page. > > This is not un unreasonable assumption to make, but on architectures > that have CONFIG_HAVE_ARCH_HUGE_VMAP=y, it no longer holds, and we need > to ensure that vmalloc_to_page() does not go off into the weeds trying > to dereference huge PUDs or PMDs as table entries. > > Given that vmalloc() and vmap() themselves never create huge mappings or > deal with compound pages at all, there is no correct answer in this > case, so return NULL instead, and issue a warning. > > When reading /proc/kcore on arm64, you will hit an oops as soon as you > hit the huge mappings used for the various segments that make up the > mapping of vmlinux. With this patch applied, you will no longer hit the > oops, but the kcore contents willl be incorrect (these regions will be > zeroed out) > > We are fixing this for kcore specifically, so it avoids vread() for > those regions. At least one other problematic user exists, i.e., > /dev/kmem, but that is currently broken on arm64 for other reasons. > > Link: http://lkml.kernel.org/r/20170609082226.26152-1-ard.biesheuvel@xxxxxxxxxx > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > Acked-by: Mark Rutland <mark.rutland@xxxxxxx> > Reviewed-by: Laura Abbott <labbott@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: zhong jiang <zhongjiang@xxxxxxxxxx> > Cc: Dave Hansen <dave.hansen@xxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > (cherry picked from commit 029c54b09599573015a5c18dbe59cbdf42742237) > [ardb: non-trivial backport to v4.9] Thanks for this, now queued up. greg k-h