If align < sizeof(*metadata), metadata_space is set to zero. In this case
ALIGN_UP(intptr + metadata_space, align) returns intptr if intptr was
already aligned at align, which is pretty much always the case. That way we
underflow when storing metadata.
+ add an assert to detect this kind of underflows.
+ call ALIGN_UP with intptr + sizeof(*metadata) instead of
intptr + metadata_space.
+ rename metadata_space to padding which is a more sensible name
Signed-off-by: Hugo Lefeuvre <hugo.lefeuvre@xxxxxxxxx>
---
lib/ukalloc/alloc.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)
diff --git a/lib/ukalloc/alloc.c b/lib/ukalloc/alloc.c
index b1946dc..2d16057 100644
--- a/lib/ukalloc/alloc.c
+++ b/lib/ukalloc/alloc.c
@@ -235,7 +235,7 @@ int uk_posix_memalign_ifpages(struct uk_alloc *a,
struct metadata_ifpages *metadata;
unsigned long num_pages;
uintptr_t intptr;
- size_t realsize, metadata_space;
+ size_t realsize, padding;
UK_ASSERT(a);
if (((align - 1) & align) != 0
@@ -259,27 +259,32 @@ int uk_posix_memalign_ifpages(struct uk_alloc *a,
* the requested alignment.
*/
if (align >= __PAGE_SIZE) {
- metadata_space = __PAGE_SIZE;
- } else if (align < sizeof(*metadata)) {
- metadata_space = 0;
+ padding = __PAGE_SIZE;
+ } else if (align < METADATA_IFPAGES_SIZE_POW2) {
align = METADATA_IFPAGES_SIZE_POW2;
+ padding = 0;
} else {
- metadata_space = sizeof(*metadata);
+ padding = sizeof(*metadata);
}
/* In addition to metadata space, allocate `align` more bytes in
* order to be sure to find an aligned pointer preceding `size` bytes.
*/
- realsize = size + metadata_space + align;
+ realsize = size + padding + align;
num_pages = size_to_num_pages(realsize);
intptr = (uintptr_t) uk_palloc(a, num_pages);
if (!intptr)
return ENOMEM;
- *memptr = (void *) ALIGN_UP(intptr + metadata_space, (uintptr_t) align);
+ *memptr = (void *) ALIGN_UP(intptr + sizeof(*metadata),
+ (uintptr_t) align);
metadata = uk_get_metadata(*memptr);
+
+ /* check for underflow */
+ UK_ASSERT(intptr <= (uintptr_t) metadata) > +
metadata->num_pages = num_pages;
metadata->base = (void *) intptr;
