Re: [PATCH v2] Drivers: hv: mshv: fix integer overflow in memory region overlap check

[Junrui Luo]

On Fri, Apr 10, 2026 at 09:05:35PM -0800, v...@mailbox.org wrote:
> All in all, from the three options of (generic check for overflow, simple 
> check
> for arch bad PFNs/GFNs, an elaborated check with all specifics) I suggested 
> the simple check.
> Fast and still more useful than checking for overflow in my opinion.
 
Thanks Roman for the thorough write-up. Since the original patch mixes
host and hypervisor-side constants with an unclear unit, IMO we should
do the bounds check in bytes instead.

For instance:

        u64 start_gpa, end_gpa;

        if (check_mul_overflow(mem->guest_pfn, HV_HYP_PAGE_SIZE,
                                                   &start_gpa) ||
                check_add_overflow(start_gpa, mem->size, &end_gpa) ||
                end_gpa > (1ULL << MAX_PHYSMEM_BITS))
                return -EINVAL;

Both sides of the final comparison are bytes, so no host-vs-hv page
unit conversion is needed.

In addition, it changes return value from -EOVERFLOW to -EINVAL.

Does this approach look reasonable? Happy to iterate if either of you
would prefer a different choice.

Thanks,
Junrui Luo