[Xen-changelog] [xen stable-4.2] x86/xsave: initialize extended register state when guests enable it

[patchbot@xxxxxxx]

commit 12b0ee04a16194f064d5b895a844fcdc6414bfc0
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Sep 25 10:55:42 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Sep 25 10:55:42 2013 +0200

    x86/xsave: initialize extended register state when guests enable it
    
    Till now, when setting previously unset bits in XCR0 we wouldn't touch
    the active register state, thus leaving in the newly enabled registers
    whatever a prior user of it left there, i.e. potentially leaking
    information between guests.
    
    This is CVE-2013-1442 / XSA-62.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 63a75ba0de817d6f384f96d25427a05c313e2179
    master date: 2013-09-25 10:41:25 +0200
---
 xen/arch/x86/xstate.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
index b0ac1ff..37c5225 100644
--- a/xen/arch/x86/xstate.c
+++ b/xen/arch/x86/xstate.c
@@ -348,6 +348,7 @@ int validate_xstate(u64 xcr0, u64 xcr0_accum, u64 
xstate_bv, u64 xfeat_mask)
 int handle_xsetbv(u32 index, u64 new_bv)
 {
     struct vcpu *curr = current;
+    u64 mask;
 
     if ( index != XCR_XFEATURE_ENABLED_MASK )
         return -EOPNOTSUPP;
@@ -361,9 +362,23 @@ int handle_xsetbv(u32 index, u64 new_bv)
     if ( !set_xcr0(new_bv) )
         return -EFAULT;
 
+    mask = new_bv & ~curr->arch.xcr0_accum;
     curr->arch.xcr0 = new_bv;
     curr->arch.xcr0_accum |= new_bv;
 
+    mask &= curr->fpu_dirtied ? ~XSTATE_FP_SSE : XSTATE_NONLAZY;
+    if ( mask )
+    {
+        unsigned long cr0 = read_cr0();
+
+        clts();
+        if ( curr->fpu_dirtied )
+            asm ( "stmxcsr %0" : "=m" (curr->arch.xsave_area->fpu_sse.mxcsr) );
+        xrstor(curr, mask);
+        if ( cr0 & X86_CR0_TS )
+            write_cr0(cr0);
+    }
+
     return 0;
 }
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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