Re: [Xen-devel] [PATCH] x86-64: don't allow non-canonical addresses to be set for any callback

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 13.06.12 at 12:51, David Vrabel <dvrabel@xxxxxxxxxx> wrote:
> On 13/06/12 11:02, Jan Beulich wrote:
>> Rather than deferring the detection of these to the point where they
>> get actually used (the fix for XSA-7, 25480:76eaf5966c05, causing a #GP
>> to be raised by IRET, which invokes the guest's [fragile] fail-safe
>> callback), don't even allow such to be set.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> 
>> --- a/xen/arch/x86/domain.c
>> +++ b/xen/arch/x86/domain.c
>> @@ -736,6 +736,14 @@ int arch_set_info_guest(
>>      {
>>          if ( !compat )
>>          {
>> +#ifdef __x86_64__
>> +            if ( !is_canonical_address(c.nat->user_regs.eip) ||
>> +                 !is_canonical_address(c.nat->event_callback_eip) ||
>> +                 !is_canonical_address(c.nat->syscall_callback_eip) ||
>> +                 !is_canonical_address(c.nat->failsafe_callback_eip) )
>> +                return -EINVAL;
>> +#endif
>> +
> 
> Would it be better to have
> 
> #ifndef __x86_64__
> #  define is_canonical_address(a) 1
> #endif
> 
> somewhere?

That one we have (otherwise other changes in this patch would
cause build failures), the problem here is that ->syscall_callback
doesn't exist for the 32-bit interface. And rater than just putting
that on line into a conditional, I preferred to frame the whole
addition.

Jan


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