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

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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




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