Re: [PATCH v2 6/7] KVM: VMX: Check Intel PT related CPUID leaves

[Paolo Bonzini]

On 10/09/21 03:59, Xiaoyao Li wrote:
> > Ugh, looking at the rest of the code, even this isn't sufficient
> > because pt_desc.guest.addr_{a,b} are hardcoded at 4 entries, i.e.
> > running KVM on hardware with >4 entries will lead to buffer
> > overflows.
>
> it's hardcoded to 4 because there is a note of "no processors support
>  more than 4 address ranges" in SDM vol.3 Chapter 31.3.1, table
> 31-11

True, but I agree with Sean that it's not pretty.

> > One option would be to bump that to the theoretical max of 15,
> > which doesn't seem too horrible, especially if pt_desc as a whole
> > is allocated on-demand, which it probably should be since it isn't
> > exactly tiny (nor ubiquitous)
> >
> > A different option would be to let userspace define whatever it
> > wants for guest CPUID, and instead cap nr_addr_ranges at
> > min(host.cpuid, guest.cpuid, RTIT_ADDR_RANGE).

This is the safest option.

Paolo