36 lines
1.4 KiB
Diff
36 lines
1.4 KiB
Diff
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# Commit 7cfb0053629c4dd1a6f01dc43cca7c0c25b8b7bf
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# Date 2013-10-04 12:24:34 +0200
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# Author Andrew Cooper <andrew.cooper3@citrix.com>
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# Committer Jan Beulich <jbeulich@suse.com>
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x86/percpu: Force INVALID_PERCPU_AREA into the non-canonical address region
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This causes accidental uses of per_cpu() on a pcpu with an INVALID_PERCPU_AREA
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to result in a #GF for attempting to access the middle of the non-canonical
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virtual address region.
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This is preferable to the current behaviour, where incorrect use of per_cpu()
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will result in an effective NULL structure dereference which has security
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implication in the context of PV guests.
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Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
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Acked-by: Keir Fraser <keir@xen.org>
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--- a/xen/arch/x86/percpu.c
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+++ b/xen/arch/x86/percpu.c
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@@ -6,7 +6,14 @@
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#include <xen/rcupdate.h>
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unsigned long __per_cpu_offset[NR_CPUS];
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-#define INVALID_PERCPU_AREA (-(long)__per_cpu_start)
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+
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+/*
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+ * Force uses of per_cpu() with an invalid area to attempt to access the
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+ * middle of the non-canonical address space resulting in a #GP, rather than a
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+ * possible #PF at (NULL + a little) which has security implications in the
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+ * context of PV guests.
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+ */
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+#define INVALID_PERCPU_AREA (0x8000000000000000L - (long)__per_cpu_start)
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#define PERCPU_ORDER (get_order_from_bytes(__per_cpu_data_end-__per_cpu_start))
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void __init percpu_init_areas(void)
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