malloc: fix ASan handling for unmapped memory

Currently, when we free previously allocated memory, we mark the area as
"freed" for ASan purposes (flag 0xfd). However, sometimes, freeing a
malloc element will cause pages to be unmapped from memory and re-backed
with anonymous memory again. This may cause ASan's "use-after-free"
error down the line, because the allocator will try to write into
memory areas recently marked as "freed".

To fix this, we need to mark the unmapped memory area as "available",
and fixup surrounding malloc element header/trailers to enable later
malloc routines to safely write into new malloc elements' headers or
trailers.

Bugzilla ID: 994
Fixes: 6cc51b1293ce ("mem: instrument allocator for ASan")
Cc: stable@dpdk.org
Reported-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>

diff --git a/lib/eal/common/malloc_elem.h b/lib/eal/common/malloc_elem.h
index f2aa98821be99feab9cf25a0d52439dbdd32c9fd..c5f65895e101778f1110ce6bc3e17b1d24ff75b8 100644 (file)
--- a/lib/eal/common/malloc_elem.h
+++ b/lib/eal/common/malloc_elem.h
@@ -278,6 +278,10 @@ old_malloc_size(struct malloc_elem *elem)
 
 #define __rte_no_asan
 
+static inline void
+asan_set_zone(void *ptr __rte_unused, size_t len __rte_unused,
+               uint32_t val __rte_unused) { }
+
 static inline void
 asan_set_freezone(void *ptr __rte_unused, size_t size __rte_unused) { }
 

diff --git a/lib/eal/common/malloc_heap.c b/lib/eal/common/malloc_heap.c
index 6c572b6f2cd6d54a8a473b19ba5d299fc4e26f92..a3d26fcbea78cdf6980391d7d83d92dd20bf8ed3 100644 (file)
--- a/lib/eal/common/malloc_heap.c
+++ b/lib/eal/common/malloc_heap.c
@@ -861,6 +861,7 @@ malloc_heap_free(struct malloc_elem *elem)
        struct rte_memseg_list *msl;
        unsigned int i, n_segs, before_space, after_space;
        int ret;
+       bool unmapped = false;
        const struct internal_config *internal_conf =
                eal_get_internal_configuration();
 
@@ -1027,6 +1028,9 @@ malloc_heap_free(struct malloc_elem *elem)
                request_to_primary(&req);
        }
 
+       /* we didn't exit early, meaning we have unmapped some pages */
+       unmapped = true;
+
        RTE_LOG(DEBUG, EAL, "Heap on socket %d was shrunk by %zdMB\n",
                msl->socket_id, aligned_len >> 20ULL);
 
@@ -1034,6 +1038,37 @@ malloc_heap_free(struct malloc_elem *elem)
 free_unlock:
        asan_set_freezone(asan_ptr, asan_data_len);
 
+       /* if we unmapped some memory, we need to do additional work for ASan */
+       if (unmapped) {
+               void *asan_end = RTE_PTR_ADD(asan_ptr, asan_data_len);
+               void *aligned_end = RTE_PTR_ADD(aligned_start, aligned_len);
+               void *aligned_trailer = RTE_PTR_SUB(aligned_start,
+                               MALLOC_ELEM_TRAILER_LEN);
+
+               /*
+                * There was a memory area that was unmapped. This memory area
+                * will have to be marked as available for ASan, because we will
+                * want to use it next time it gets mapped again. The OS memory
+                * protection should trigger a fault on access to these areas
+                * anyway, so we are not giving up any protection.
+                */
+               asan_set_zone(aligned_start, aligned_len, 0x00);
+
+               /*
+                * ...however, when we unmap pages, we create new free elements
+                * which might have been marked as "freed" with an earlier
+                * `asan_set_freezone` call. So, if there is an area past the
+                * unmapped space that was marked as freezone for ASan, we need
+                * to mark the malloc header as available.
+                */
+               if (asan_end > aligned_end)
+                       asan_set_zone(aligned_end, MALLOC_ELEM_HEADER_LEN, 0x00);
+
+               /* if there's space before unmapped memory, mark as available */
+               if (asan_ptr < aligned_start)
+                       asan_set_zone(aligned_trailer, MALLOC_ELEM_TRAILER_LEN, 0x00);
+       }
+
        rte_spinlock_unlock(&(heap->lock));
        return ret;
 }