CVE-2022-50167: Integer Overflow or Wraparound

In the Linux kernel, the following vulnerability has been resolved:

bpf: fix potential 32-bit overflow when accessing ARRAY map element

If BPF array map is bigger than 4GB, element pointer calculation can overflow because both index and elem_size are u32. Fix this everywhere by forcing 64-bit multiplication. Extract this formula into separate small helper and use it consistently in various places.

Speculative-preventing formula utilizing index_mask trick is left as is, but explicit u64 casts are added in both places.