Re: [Xen-devel] [PATCH] VMX: don't crash processing 'd' debug key

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.11.13 at 15:34, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 07/11/13 10:44, Jan Beulich wrote:
>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> @@ -675,7 +675,17 @@ void vmx_get_segment_register(struct vcp
>>  {
>>      unsigned long attr = 0, sel = 0, limit;
>>  
>> -    vmx_vmcs_enter(v);
>> +    /*
>> +     * We may get here in the context of dump_execstate(), which may have
>> +     * interrupted context switching between setting "current" and
>> +     * vmx_do_resume() reaching the end of vmx_load_vmcs(). That would make
>> +     * all the VMREADs below fail if we don't bail right away.
>> +     */
>> +    if ( unlikely(!vmx_vmcs_enter(v)) )
>> +    {
>> +        memset(reg, 0, sizeof(*reg));
>> +        return;
>> +    }
> 
> What are the implications of this?  All callers unconditionally expect
> this to succeed, and use the results straight as-are.
> 
> On the other hand, I am not certain how we could go about dealing with
> the error.

The thing is that for all "normal" code paths we won't get there.
Hence it'll only be that - rather than crashing - no useful
information will be displayed for the debug key. (And obviously,
should vmx_vmcs_enter() nevertheless end up failing on a
"normal" code path, all callers properly looking at the results
should produce #GP faults to the guest [present bit clear,
minimal permissions, and segment limit zero].)

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel