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?
>
> 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;
> }
>
