[Xen-changelog] [xen stable-4.3] x86: check segment descriptor read result in 64-bit OUTS emulation

[patchbot@xxxxxxx]

commit 889f547790953d30cd88a465aac5954e5f407e53
Author:     Matthew Daley <mattjd@xxxxxxxxx>
AuthorDate: Thu Oct 10 15:22:55 2013 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Oct 10 15:22:55 2013 +0200

    x86: check segment descriptor read result in 64-bit OUTS emulation
    
    When emulating such an operation from a 64-bit context (CS has long
    mode set), and the data segment is overridden to FS/GS, the result of
    reading the overridden segment's descriptor (read_descriptor) is not
    checked. If it fails, data_base is left uninitialized.
    
    This can lead to 8 bytes of Xen's stack being leaked to the guest
    (implicitly, i.e. via the address given in a #PF).
    
    Coverity-ID: 1055116
    
    This is CVE-2013-4368 / XSA-67.
    
    Signed-off-by: Matthew Daley <mattjd@xxxxxxxxx>
    
    Fix formatting.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 0771faba163769089c9f05f7f76b63e397677613
    master date: 2013-10-10 15:19:53 +0200
---
 xen/arch/x86/traps.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 2e6895c..eb426ec 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1990,10 +1990,10 @@ static int emulate_privileged_op(struct cpu_user_regs 
*regs)
                     break;
                 }
             }
-            else
-                read_descriptor(data_sel, v, regs,
-                                &data_base, &data_limit, &ar,
-                                0);
+            else if ( !read_descriptor(data_sel, v, regs,
+                                       &data_base, &data_limit, &ar, 0) ||
+                      !(ar & _SEGMENT_S) || !(ar & _SEGMENT_P) )
+                goto fail;
             data_limit = ~0UL;
             ar = _SEGMENT_WR|_SEGMENT_S|_SEGMENT_DPL|_SEGMENT_P;
         }
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.3

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