xen/blkif: avoid double access to any shared ring request fields
Commit f9e98e5d7a
("xen/blkif: Avoid double access to
src->nr_segments") didn't go far enough: src->operation is also being
used twice. And nothing was done to prevent the compiler from using the
source side of the copy done by blk_get_request() (granted that's very
unlikely).
Move the barrier()s up, and add another one to blk_get_request().
Note that for completing XSA-155, the barrier() getting added to
blk_get_request() would suffice, and hence the changes to xen_blkif.h
are more like just cleanup. And since, as said, the unpatched code
getting compiled to something vulnerable is very unlikely (and not
observed in practice), this isn't being viewed as a new security issue.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
This commit is contained in:
parent
55e5c3a2d2
commit
4837a1a516
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@ -79,14 +79,14 @@ static inline void blkif_get_x86_32_req(blkif_request_t *dst, blkif_x86_32_reque
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dst->handle = src->handle;
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dst->handle = src->handle;
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dst->id = src->id;
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dst->id = src->id;
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dst->sector_number = src->sector_number;
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dst->sector_number = src->sector_number;
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if (src->operation == BLKIF_OP_DISCARD) {
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/* Prevent the compiler from using src->... instead. */
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barrier();
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if (dst->operation == BLKIF_OP_DISCARD) {
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struct blkif_request_discard *s = (void *)src;
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struct blkif_request_discard *s = (void *)src;
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struct blkif_request_discard *d = (void *)dst;
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struct blkif_request_discard *d = (void *)dst;
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d->nr_sectors = s->nr_sectors;
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d->nr_sectors = s->nr_sectors;
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return;
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return;
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}
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}
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/* prevent the compiler from optimizing the code and using src->nr_segments instead */
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barrier();
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if (n > dst->nr_segments)
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if (n > dst->nr_segments)
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n = dst->nr_segments;
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n = dst->nr_segments;
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for (i = 0; i < n; i++)
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for (i = 0; i < n; i++)
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@ -102,14 +102,14 @@ static inline void blkif_get_x86_64_req(blkif_request_t *dst, blkif_x86_64_reque
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dst->handle = src->handle;
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dst->handle = src->handle;
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dst->id = src->id;
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dst->id = src->id;
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dst->sector_number = src->sector_number;
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dst->sector_number = src->sector_number;
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if (src->operation == BLKIF_OP_DISCARD) {
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/* Prevent the compiler from using src->... instead. */
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barrier();
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if (dst->operation == BLKIF_OP_DISCARD) {
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struct blkif_request_discard *s = (void *)src;
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struct blkif_request_discard *s = (void *)src;
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struct blkif_request_discard *d = (void *)dst;
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struct blkif_request_discard *d = (void *)dst;
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d->nr_sectors = s->nr_sectors;
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d->nr_sectors = s->nr_sectors;
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return;
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return;
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}
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}
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/* prevent the compiler from optimizing the code and using src->nr_segments instead */
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barrier();
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if (n > dst->nr_segments)
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if (n > dst->nr_segments)
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n = dst->nr_segments;
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n = dst->nr_segments;
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for (i = 0; i < n; i++)
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for (i = 0; i < n; i++)
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@ -679,6 +679,8 @@ static int blk_get_request(struct XenBlkDev *blkdev, struct ioreq *ioreq, RING_I
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RING_GET_REQUEST(&blkdev->rings.x86_64_part, rc));
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RING_GET_REQUEST(&blkdev->rings.x86_64_part, rc));
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break;
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break;
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}
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}
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/* Prevent the compiler from accessing the on-ring fields instead. */
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barrier();
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return 0;
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return 0;
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}
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}
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