| Message ID | 20191122112621.204798-23-glider@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add KernelMemorySanitizer infrastructure | expand |
On Fri, 22 Nov 2019 at 12:27, <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. > > 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 > --- > 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? Thanks, -- Marco
On Mon, Dec 2, 2019 at 4:37 PM Marco Elver <elver@google.com> wrote: > > On Fri, 22 Nov 2019 at 12:27, <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. > > > > 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 > > --- > > 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
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(). + */ 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. @@ -2776,6 +2796,7 @@ 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; @@ -3157,7 +3178,7 @@ 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); @@ -3198,11 +3219,11 @@ 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); @@ -3803,6 +3824,7 @@ 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; @@ -5717,6 +5739,7 @@ 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; } @@ -5866,6 +5889,7 @@ 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; }
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@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 --- v3: - reverted unrelated whitespace changes Change-Id: I51103b7981d3aabed747d0c85cbdc85568665871 --- mm/slub.c | 34 +++++++++++++++++++++++++++++----- 1 file changed, 29 insertions(+), 5 deletions(-)