Re: [PATCH RFC v1 18/26] kmsan: mm: call KMSAN hooks from SLUB code

[Qian Cai <cai@lca.pw>]

On Fri, 2019-10-18 at 11:42 +0200, glider@google.com 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@google.com>
> To: Alexander Potapenko <glider@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Vegard Nossum <vegard.nossum@oracle.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: linux-mm@kvack.org
> ---
> 
> 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;
>  }
>