Commit f9e98e5d authored by Stefano Stabellini's avatar Stefano Stabellini
Browse files

xen/blkif: Avoid double access to src->nr_segments 



src is stored in shared memory and src->nr_segments is dereferenced
twice at the end of the function.  If a compiler decides to compile this
into two separate memory accesses then the size limitation could be
bypassed.

Fix it by removing the double access to src->nr_segments.

This is part of XSA-155.

Signed-off-by: default avatarStefano Stabellini <stefano.stabellini@eu.citrix.com>
parent 18f49881

hw/block/xen_blkif.h

+8 −4
Original line number Diff line number Diff line
@@ -85,8 +85,10 @@ static inline void blkif_get_x86_32_req(blkif_request_t *dst, blkif_x86_32_reque 
		d->nr_sectors = s->nr_sectors;

		return;

	}

	if (n > src->nr_segments)

		n = src->nr_segments;

	/* prevent the compiler from optimizing the code and using src->nr_segments instead */

	barrier();

	if (n > dst->nr_segments)

		n = dst->nr_segments;

	for (i = 0; i < n; i++)

		dst->seg[i] = src->seg[i];

}
@@ -106,8 +108,10 @@ static inline void blkif_get_x86_64_req(blkif_request_t *dst, blkif_x86_64_reque 
		d->nr_sectors = s->nr_sectors;

		return;

	}

	if (n > src->nr_segments)

		n = src->nr_segments;

	/* prevent the compiler from optimizing the code and using src->nr_segments instead */

	barrier();

	if (n > dst->nr_segments)

		n = dst->nr_segments;

	for (i = 0; i < n; i++)

		dst->seg[i] = src->seg[i];

}