On Fri, Oct 18, 2019 at 3:22 PM Qian Cai <cai@xxxxxx> wrote:
>
> On Fri, 2019-10-18 at 11:42 +0200, 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.
>
> Well, there is SLUB debug which has red zoning and poisoning checks. What's
> value of this patch?
Sorry, are you talking about the whole patchset or just this patch?
Note that SLUB debug is unable to detect uninitialized values with
bit-to-bit precision, neither have I heard of anyone using it for
detecting uses of uninitialized memory in the kernel at all.
The purpose of SLUB debug is to detect corruptions of freed memory.
> >
> > 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
> > ---
> >
> > Change-Id: I51103b7981d3aabed747d0c85cbdc85568665871
> > ---
> > mm/slub.c | 37 +++++++++++++++++++++++++++++++------
> > 1 file changed, 31 insertions(+), 6 deletions(-)
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 3d63ae320d31..3d6d4c63446e 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().
> > + */
> > static inline void *get_freepointer_safe(struct kmem_cache *s, void *object)
> > {
> > unsigned long freepointer_addr;
> > void *p;
> >
> > if (!debug_pagealloc_enabled())
> > - return get_freepointer(s, object);
> > + return KMSAN_INIT_VALUE(get_freepointer(s, object));
> >
> > freepointer_addr = (unsigned long)object + s->offset;
> > probe_kernel_read(&p, (void **)freepointer_addr, sizeof(p));
> > - return freelist_ptr(s, p, freepointer_addr);
> > + return KMSAN_INIT_VALUE(freelist_ptr(s, p, freepointer_addr));
> > }
> >
> > static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
> > @@ -1390,6 +1402,7 @@ static inline void *kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags)
> > ptr = kasan_kmalloc_large(ptr, size, flags);
> > /* As ptr might get tagged, call kmemleak hook after KASAN. */
> > kmemleak_alloc(ptr, size, 1, flags);
> > + kmsan_kmalloc_large(ptr, size, flags);
> > return ptr;
> > }
> >
> > @@ -1397,6 +1410,7 @@ static __always_inline void kfree_hook(void *x)
> > {
> > kmemleak_free(x);
> > kasan_kfree_large(x, _RET_IP_);
> > + kmsan_kfree_large(x);
> > }
> >
> > static __always_inline bool slab_free_hook(struct kmem_cache *s, void *x)
> > @@ -1453,6 +1467,12 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s,
> > } while (object != old_tail);
> > }
> >
> > + do {
> > + object = next;
> > + next = get_freepointer(s, object);
> > + kmsan_slab_free(s, object);
> > + } while (object != old_tail);
> > +
> > /*
> > * Compiler cannot detect this function can be removed if slab_free_hook()
> > * evaluates to nothing. Thus, catch all relevant config debug options here.
> > @@ -2769,6 +2789,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
> > if (unlikely(slab_want_init_on_alloc(gfpflags, s)) && object)
> > memset(object, 0, s->object_size);
> >
> > + kmsan_slab_alloc(s, object, gfpflags);
> > slab_post_alloc_hook(s, gfpflags, 1, &object);
> >
> > return object;
> > @@ -2797,6 +2818,7 @@ void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
> > void *ret = slab_alloc(s, gfpflags, _RET_IP_);
> > trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags);
> > ret = kasan_kmalloc(s, ret, size, gfpflags);
> > +
> > return ret;
> > }
> > EXPORT_SYMBOL(kmem_cache_alloc_trace);
> > @@ -2809,7 +2831,6 @@ void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags, int node)
> >
> > trace_kmem_cache_alloc_node(_RET_IP_, ret,
> > s->object_size, s->size, gfpflags, node);
> > -
> > return ret;
> > }
> > EXPORT_SYMBOL(kmem_cache_alloc_node);
> > @@ -2825,6 +2846,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
> > size, s->size, gfpflags, node);
> >
> > ret = kasan_kmalloc(s, ret, size, gfpflags);
> > +
> > return ret;
> > }
> > EXPORT_SYMBOL(kmem_cache_alloc_node_trace);
> > @@ -3150,7 +3172,7 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
> > void **p)
> > {
> > struct kmem_cache_cpu *c;
> > - int i;
> > + int i, j;
> >
> > /* memcg and kmem_cache debug support */
> > s = slab_pre_alloc_hook(s, flags);
> > @@ -3188,11 +3210,11 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
> >
> > /* Clear memory outside IRQ disabled fastpath loop */
> > if (unlikely(slab_want_init_on_alloc(flags, s))) {
> > - int j;
> > -
> > for (j = 0; j < i; j++)
> > memset(p[j], 0, s->object_size);
> > }
> > + for (j = 0; j < i; j++)
> > + kmsan_slab_alloc(s, p[j], flags);
> >
> > /* memcg and kmem_cache debug support */
> > slab_post_alloc_hook(s, flags, size, p);
> > @@ -3793,6 +3815,7 @@ static int __init setup_slub_min_objects(char *str)
> >
> > __setup("slub_min_objects=", setup_slub_min_objects);
> >
> > +__no_sanitize_memory
> > void *__kmalloc(size_t size, gfp_t flags)
> > {
> > struct kmem_cache *s;
> > @@ -5698,6 +5721,7 @@ static char *create_unique_id(struct kmem_cache *s)
> > p += sprintf(p, "%07u", s->size);
> >
> > BUG_ON(p > name + ID_STR_LENGTH - 1);
> > + kmsan_unpoison_shadow(name, p - name);
> > return name;
> > }
> >
> > @@ -5847,6 +5871,7 @@ static int sysfs_slab_alias(struct kmem_cache *s, const char *name)
> > al->name = name;
> > al->next = alias_list;
> > alias_list = al;
> > + kmsan_unpoison_shadow(al, sizeof(struct saved_alias));
> > return 0;
> > }
> >
--
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
