On Mon, Dec 2, 2019 at 4:37 PM Marco Elver <elver@xxxxxxxxxx> wrote: > > On Fri, 22 Nov 2019 at 12:27, <glider@xxxxxxxxxx> wrote: > > > > In order to report uninitialized memory coming from heap allocations > > KMSAN has to poison them unless they're created with __GFP_ZERO. > > > > It's handy that we need KMSAN hooks in the places where > > init_on_alloc/init_on_free initialization is performed. > > > > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx> > > To: Alexander Potapenko <glider@xxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx> > > Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > > Cc: linux-mm@xxxxxxxxx > > --- > > v3: > > - reverted unrelated whitespace changes > > > > Change-Id: I51103b7981d3aabed747d0c85cbdc85568665871 > > --- > > mm/slub.c | 34 +++++++++++++++++++++++++++++----- > > 1 file changed, 29 insertions(+), 5 deletions(-) > > > > diff --git a/mm/slub.c b/mm/slub.c > > index b25c807a111f..b5d2be1ac755 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -21,6 +21,8 @@ > > #include <linux/proc_fs.h> > > #include <linux/seq_file.h> > > #include <linux/kasan.h> > > +#include <linux/kmsan.h> > > +#include <linux/kmsan-checks.h> /* KMSAN_INIT_VALUE */ > > #include <linux/cpu.h> > > #include <linux/cpuset.h> > > #include <linux/mempolicy.h> > > @@ -285,17 +287,27 @@ static void prefetch_freepointer(const struct kmem_cache *s, void *object) > > prefetch(object + s->offset); > > } > > > > +/* > > + * When running under KMSAN, get_freepointer_safe() may return an uninitialized > > + * pointer value in the case the current thread loses the race for the next > > + * memory chunk in the freelist. In that case this_cpu_cmpxchg_double() in > > + * slab_alloc_node() will fail, so the uninitialized value won't be used, but > > + * KMSAN will still check all arguments of cmpxchg because of imperfect > > + * handling of inline assembly. > > + * To work around this problem, use KMSAN_INIT_VALUE() to force initialize the > > + * return value of get_freepointer_safe(). > > + */ > > Isn't this a general problem with cmpxchg? I.e. does other code using > it have the same problem? > > Would it be better to just use KMSAN_INIT_VALUE in cmpxchg, rather > than having the one-off workaround here? I don't think so. It's normally still an error to pass an uninitialized arg to cmpxchg, as in other cases it may be copied to the result. > Thanks, > -- Marco -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
