44 lines
1.4 KiB
Diff
44 lines
1.4 KiB
Diff
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xen/blkif: Avoid double access to src->nr_segments
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src is stored in shared memory and src->nr_segments is dereferenced
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twice at the end of the function. If a compiler decides to compile this
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into two separate memory accesses then the size limitation could be
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bypassed.
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Fix it by removing the double access to src->nr_segments.
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This is part of XSA-155.
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Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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Index: xen-4.6.0-testing/tools/qemu-xen-dir-remote/hw/block/xen_blkif.h
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===================================================================
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--- xen-4.6.0-testing.orig/tools/qemu-xen-dir-remote/hw/block/xen_blkif.h
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+++ xen-4.6.0-testing/tools/qemu-xen-dir-remote/hw/block/xen_blkif.h
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@@ -85,8 +85,10 @@ static inline void blkif_get_x86_32_req(
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d->nr_sectors = s->nr_sectors;
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return;
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}
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- if (n > src->nr_segments)
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- n = src->nr_segments;
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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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+ n = dst->nr_segments;
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for (i = 0; i < n; i++)
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dst->seg[i] = src->seg[i];
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}
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@@ -106,8 +108,10 @@ static inline void blkif_get_x86_64_req(
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d->nr_sectors = s->nr_sectors;
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return;
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}
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- if (n > src->nr_segments)
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- n = src->nr_segments;
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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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+ n = dst->nr_segments;
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for (i = 0; i < n; i++)
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dst->seg[i] = src->seg[i];
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}
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