[Xen-changelog] [xen master] x86/xsave: recover from faults on XRSTOR

[patchbot@xxxxxxx]

commit c6ae65db36b98f2866f74a9a7ae6ac5d51fedc67
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 4 09:27:58 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 4 09:27:58 2013 +0200

    x86/xsave: recover from faults on XRSTOR
    
    Just like FXRSTOR, XRSTOR can raise #GP if bad content is being passed
    to it in the memory block (i.e. aspects not under the control of the
    hypervisor, other than e.g. proper alignment of the block).
    
    Also correct the comment explaining why FXRSTOR needs exception
    recovery code to not wrongly state that this can only be a result of
    the control tools passing a bad image.
    
    This is CVE-2013-2077 / XSA-53.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/i387.c   |    2 +-
 xen/arch/x86/xstate.c |   23 +++++++++++++++++++----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c
index 9127037..8873885 100644
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -53,7 +53,7 @@ static inline void fpu_fxrstor(struct vcpu *v)
     /*
      * FXRSTOR can fault if passed a corrupted data block. We handle this
      * possibility, which may occur if the block was passed to us by control
-     * tools, by silently clearing the block.
+     * tools or through VCPUOP_initialise, by silently clearing the block.
      */
     asm volatile (
         /* See above for why the operands/constraints are this way. */
diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index 9fe5eec..a0d036d 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -93,10 +93,25 @@ void xrstor(struct vcpu *v, uint64_t mask)
                        "fildl %0"          /* load to clear state */
                        : : "m" (ptr->fpu_sse) );
 
-    asm volatile (
-        ".byte " REX_PREFIX "0x0f,0xae,0x2f"
-        :
-        : "m" (*ptr), "a" (lmask), "d" (hmask), "D"(ptr) );
+    /*
+     * XRSTOR can fault if passed a corrupted data block. We handle this
+     * possibility, which may occur if the block was passed to us by control
+     * tools or through VCPUOP_initialise, by silently clearing the block.
+     */
+    asm volatile ( "1: .byte " REX_PREFIX "0x0f,0xae,0x2f\n"
+                   ".section .fixup,\"ax\"\n"
+                   "2: mov %5,%%ecx       \n"
+                   "   xor %1,%1          \n"
+                   "   rep stosb          \n"
+                   "   lea %2,%0          \n"
+                   "   mov %3,%1          \n"
+                   "   jmp 1b             \n"
+                   ".previous             \n"
+                   _ASM_EXTABLE(1b, 2b)
+                   : "+&D" (ptr), "+&a" (lmask)
+                   : "m" (*ptr), "g" (lmask), "d" (hmask),
+                     "m" (xsave_cntxt_size)
+                   : "ecx" );
 }
 
 bool_t xsave_enabled(const struct vcpu *v)
--
generated by git-patchbot for /home/xen/git/xen.git#master

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