From 7cfb0053629c4dd1a6f01dc43cca7c0c25b8b7bf Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Fri, 4 Oct 2013 12:24:34 +0200 Subject: x86/percpu: Force INVALID_PERCPU_AREA into the non-canonical address region This causes accidental uses of per_cpu() on a pcpu with an INVALID_PERCPU_AREA to result in a #GF for attempting to access the middle of the non-canonical virtual address region. This is preferable to the current behaviour, where incorrect use of per_cpu() will result in an effective NULL structure dereference which has security implication in the context of PV guests. Signed-off-by: Andrew Cooper Acked-by: Keir Fraser --- xen/arch/x86/percpu.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'xen') diff --git a/xen/arch/x86/percpu.c b/xen/arch/x86/percpu.c index e5450248ad..1c1dad9011 100644 --- a/xen/arch/x86/percpu.c +++ b/xen/arch/x86/percpu.c @@ -6,7 +6,14 @@ #include unsigned long __per_cpu_offset[NR_CPUS]; -#define INVALID_PERCPU_AREA (-(long)__per_cpu_start) + +/* + * Force uses of per_cpu() with an invalid area to attempt to access the + * middle of the non-canonical address space resulting in a #GP, rather than a + * possible #PF at (NULL + a little) which has security implications in the + * context of PV guests. + */ +#define INVALID_PERCPU_AREA (0x8000000000000000L - (long)__per_cpu_start) #define PERCPU_ORDER (get_order_from_bytes(__per_cpu_data_end-__per_cpu_start)) void __init percpu_init_areas(void) -- cgit v1.2.3