Re: [Xen-devel] [PATCH 5/9] x86/HVM: refuse CR3 loads with reserved (upper) bits set

[Jan Beulich <jbeulich@xxxxxxxx>]

On 12.09.2019 13:45, Roger Pau Monné  wrote:
> On Wed, Sep 11, 2019 at 05:24:41PM +0200, Jan Beulich wrote:
>> While bits 11 and below are, if not used for other purposes, reserved
>> but ignored, bits beyond physical address width are supposed to raise
>> exceptions (at least in the non-nested case; I'm not convinced the
>> current nested SVM/VMX behavior of raising #GP(0) here is correct, but
>> that's not the subject of this change).
>>
>> Introduce currd as a local variable, and replace other v->domain
>> instances at the same time.
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> LGTM, just two comments which are not related to functionality, so:
> 
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks.

>> --- a/xen/arch/x86/hvm/hvm.c
>> +++ b/xen/arch/x86/hvm/hvm.c
>> @@ -1004,6 +1004,13 @@ static int hvm_load_cpu_ctxt(struct doma
>>          return -EINVAL;
>>      }
>>  
>> +    if ( ctxt.cr3 & ~((1UL << d->arch.cpuid->extd.maxphysaddr) - 1) )
>> +    {
>> +        printk(XENLOG_G_ERR "HVM%d restore: bad CR3 %#" PRIx64 "\n",
> 
> gprintk would be more natural here IMO.

I don't think so, no - the %pv value additionally getting logged
by gprintk() has no real use in this case.

>> @@ -2290,10 +2297,19 @@ int hvm_set_cr0(unsigned long value, boo
>>  int hvm_set_cr3(unsigned long value, bool noflush, bool may_defer)
>>  {
>>      struct vcpu *v = current;
>> +    struct domain *currd = v->domain;
>>      struct page_info *page;
>>      unsigned long old = v->arch.hvm.guest_cr[3];
>>  
>> -    if ( may_defer && 
>> unlikely(v->domain->arch.monitor.write_ctrlreg_enabled &
>> +    if ( value & ~((1UL << currd->arch.cpuid->extd.maxphysaddr) - 1) )
> 
> I would consider introducing a macro/inline helper for this, since
> it's already used twice in this patch.

Well, yes, I could do this in a prereq patch, taking care of the
same expression in guest_pt.h. Grep-ing the tree I see a better
way of doing this though (in paging.h), and hence I guess I'll
switch both to

    if ( <VAL> >> currd->arch.cpuid->extd.maxphysaddr )

I'll take it that this wouldn't invalidate you R-b.

Jan

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