[Xen-bugs] [Bug 687] New: x86-64 Dom0 and DomU kernel crashes in page fault handler if alignment checking is enabled in eflags

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=687

           Summary: x86-64 Dom0 and DomU kernel crashes in page fault
                    handler if alignment checking is enabled in eflags
           Product: Xen
           Version: 3.0.2
          Platform: x86-64
        OS/Version: Linux-2.6
            Status: NEW
          Severity: major
          Priority: P2
         Component: Guest-OS
        AssignedTo: xen-bugs@xxxxxxxxxxxxxxxxxxx
        ReportedBy: gareth@xxxxxxxxxxxxxx


x86-64 kernel crashes in page fault handler if a user space application has
enabled alignment checking in the eflags register (i.e X86_EFLAGS_AC 
0x00040000).  The first page fault to be handled after enabling alignment
checking causes the crash.

I suspect the cause is that entry-Xen.s does not preserve / restore the eflags
in the same way as the stock Linux kernel would.

I've marked this as a major bug as it causes the DomU (or Dom0) kernel to panic
and crash immediately and could be a potential denial of service attack as it
does not require any special priveleges to cause.

Will attach a testcase shortly


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