[PATCH V2] x86/xsaves: get_xsave_addr, check xsave header and support uncompressed format

[PATCH V2] x86/xsaves: get_xsave_addr, check xsave header and support uncompressed format

[Huaitong Han]

The check needs to be against the xsave header in the area, rather than Xen's
maximum xfeature_mask. A guest might easily have a smaller xcr0 than the
maximum Xen is willing to allow, causing the pointer below to be bogus.

The get_xsave_addr() is modified to support uncompressed xstate areas.

Signed-off-by: Huaitong Han <huaitong.han@intel.com>
---
 xen/arch/x86/xstate.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index b65da38..4e87ab3 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -146,12 +146,15 @@ static void __init setup_xstate_comp(void)
     }
 }
 
-static void *get_xsave_addr(void *xsave, unsigned int xfeature_idx)
+static void *get_xsave_addr(struct xsave_struct *xsave,
+        unsigned int xfeature_idx)
 {
-    if ( !((1ul << xfeature_idx) & xfeature_mask) )
+    if ( !((1ul << xfeature_idx) & xsave->xsave_hdr.xstate_bv) )
         return NULL;
 
-    return xsave + xstate_comp_offsets[xfeature_idx];
+    return (void *)xsave + (xsave_area_compressed(xsave)
+            ? xstate_comp_offsets
+            : xstate_offsets)[xfeature_idx];
 }
 
 void expand_xsave_states(struct vcpu *v, void *dest, unsigned int size)
-- 
2.4.3

Re: [PATCH V2] x86/xsaves: get_xsave_addr, check xsave header and support uncompressed format

[Andrew Cooper]

On 18/12/15 15:03, Huaitong Han wrote:
> The check needs to be against the xsave header in the area, rather than Xen's
> maximum xfeature_mask. A guest might easily have a smaller xcr0 than the
> maximum Xen is willing to allow, causing the pointer below to be bogus.
>
> The get_xsave_addr() is modified to support uncompressed xstate areas.
>
> Signed-off-by: Huaitong Han <huaitong.han@intel.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>