[PATCH 2/3] mem: fix ASan shadow for remapped memory segments

[David Marchand <david.marchand@redhat.com>]

When releasing some memory, the allocator can choose to return some
pages to the OS. At the same time, this memory was poisoned in ASAn
shadow. Doing the latter made it impossible to remap this same page
later.
On the other hand, without this poison, the OS would pagefault in any
case for this page.

Remove the poisoning for unmapped pages.

Bugzilla ID: 994
Fixes: 6cc51b1293ce ("mem: instrument allocator for ASan")
Cc: stable@dpdk.org

Signed-off-by: David Marchand <david.marchand@redhat.com>
---
 lib/eal/common/malloc_elem.h |  4 ++++
 lib/eal/common/malloc_heap.c | 12 +++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/lib/eal/common/malloc_elem.h b/lib/eal/common/malloc_elem.h
index 228f178418..b859003722 100644
--- a/lib/eal/common/malloc_elem.h
+++ b/lib/eal/common/malloc_elem.h
@@ -272,6 +272,10 @@ old_malloc_size(struct malloc_elem *elem)
 
 #else /* !RTE_MALLOC_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 6c572b6f2c..5913d9f862 100644
--- a/lib/eal/common/malloc_heap.c
+++ b/lib/eal/common/malloc_heap.c
@@ -860,6 +860,7 @@ malloc_heap_free(struct malloc_elem *elem)
 	size_t len, aligned_len, page_sz;
 	struct rte_memseg_list *msl;
 	unsigned int i, n_segs, before_space, after_space;
+	bool unmapped_pages = false;
 	int ret;
 	const struct internal_config *internal_conf =
 		eal_get_internal_configuration();
@@ -999,6 +1000,13 @@ malloc_heap_free(struct malloc_elem *elem)
 
 		/* don't care if any of this fails */
 		malloc_heap_free_pages(aligned_start, aligned_len);
+		/*
+		 * Clear any poisoning in ASan for the associated pages so that
+		 * next time EAL maps those pages, the allocator can access
+		 * them.
+		 */
+		asan_set_zone(aligned_start, aligned_len, 0x00);
+		unmapped_pages = true;
 
 		request_sync();
 	} else {
@@ -1032,7 +1040,9 @@ malloc_heap_free(struct malloc_elem *elem)
 
 	rte_mcfg_mem_write_unlock();
 free_unlock:
-	asan_set_freezone(asan_ptr, asan_data_len);
+	/* Poison memory range if belonging to some still mapped pages. */
+	if (!unmapped_pages)
+		asan_set_freezone(asan_ptr, asan_data_len);
 
 	rte_spinlock_unlock(&(heap->lock));
 	return ret;
-- 
2.23.0