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    SubjectRe: [RFC v2] implement SL*B and stack usercopy runtime checks
    On Mon, 18 Jul 2011, Vasiliy Kulikov wrote:

    > --- a/mm/slab.c
    > +++ b/mm/slab.c
    > @@ -3844,6 +3844,40 @@ unsigned int kmem_cache_size(struct kmem_cache *cachep)
    > EXPORT_SYMBOL(kmem_cache_size);
    >
    > /*
    > + * Returns false if and only if [ptr; ptr+len) touches the slab,
    > + * but breaks objects boundaries. It doesn't check whether the
    > + * accessed object is actually allocated.
    > + */
    > +bool slab_access_ok(const void *ptr, unsigned long len)
    > +{
    > + struct page *page;
    > + struct kmem_cache *cachep = NULL;

    Why = NULL?

    > + struct slab *slabp;
    > + unsigned int objnr;
    > + unsigned long offset;
    > +
    > + if (!len)
    > + return true;
    > + if (!virt_addr_valid(ptr))
    > + return true;
    > + page = virt_to_head_page(ptr);
    > + if (!PageSlab(page))
    > + return true;
    > +
    > + cachep = page_get_cache(page);
    > + slabp = page_get_slab(page);
    > + objnr = obj_to_index(cachep, slabp, (void *)ptr);
    > + BUG_ON(objnr >= cachep->num);
    > + offset = (const char *)ptr - obj_offset(cachep) -
    > + (const char *)index_to_obj(cachep, slabp, objnr);
    > + if (offset <= obj_size(cachep) && len <= obj_size(cachep) - offset)
    > + return true;
    > +
    > + return false;
    > +}
    > +EXPORT_SYMBOL(slab_access_ok);
    > +
    > +/*
    > * This initializes kmem_list3 or resizes various caches for all nodes.
    > */
    > static int alloc_kmemlist(struct kmem_cache *cachep, gfp_t gfp)

    > --- a/mm/slub.c
    > +++ b/mm/slub.c
    > @@ -2623,6 +2623,34 @@ unsigned int kmem_cache_size(struct kmem_cache *s)
    > }
    > EXPORT_SYMBOL(kmem_cache_size);
    >
    > +/*
    > + * Returns false if and only if [ptr; ptr+len) touches the slab,
    > + * but breaks objects boundaries. It doesn't check whether the
    > + * accessed object is actually allocated.
    > + */
    > +bool slab_access_ok(const void *ptr, unsigned long len)
    > +{
    > + struct page *page;
    > + struct kmem_cache *s = NULL;

    No need to assign NULL.

    > + unsigned long offset;
    > +
    > + if (len == 0)
    > + return true;
    > + if (!virt_addr_valid(ptr))
    > + return true;
    > + page = virt_to_head_page(ptr);
    > + if (!PageSlab(page))
    > + return true;
    > +
    > + s = page->slab;
    > + offset = ((const char *)ptr - (const char *)page_address(page)) % s->size;

    Are the casts necessary? Both are pointers to void *


    > + if (offset <= s->objsize && len <= s->objsize - offset)

    If offset == s->objsize then we access the first byte after the object.


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