[Xen-changelog] [xen stable-4.1] x86/xsave: recover from faults on XRSTOR

[patchbot@xxxxxxx]

commit 5849504a03725f553195c8d80b0d595ef8334e2a
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 4 09:40:12 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 4 09:40:12 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>
    master commit: c6ae65db36b98f2866f74a9a7ae6ac5d51fedc67
    master date: 2013-06-04 09:27:58 +0200
---
 xen/arch/x86/i387.c |   25 ++++++++++++++++++++-----
 1 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c
index 6e22eba..bba14ca 100644
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -59,10 +59,25 @@ static void xrstor(struct vcpu *v)
                        "fildl %0"          /* load to clear state */
                        : : "m" (ptr->fpu_sse) );
 
-    asm volatile (
-        ".byte " REX_PREFIX "0x0f,0xae,0x2f"
-        :
-        : "m" (*ptr), "a" (-1), "d" (-1), "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 %4,%%ecx       \n"
+                   "   xor %1,%1          \n"
+                   "   rep stosb          \n"
+                   "   lea %3,%0          \n"
+                   "   dec %1             \n"
+                   "   jmp 1b             \n"
+                   ".previous             \n"
+                   _ASM_EXTABLE(1b, 2b)
+                   : "+&D" (ptr)
+                   : "a" (-1), "d" (-1), "m" (*ptr),
+                     "m" (xsave_cntxt_size)
+                   : "ecx" );
 }
 
 static void load_mxcsr(unsigned long val)
@@ -196,7 +211,7 @@ static void restore_fpu(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.
      */
     if ( cpu_has_fxsr )
     {
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.1

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