CVE-2021-46974

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

bpf: Fix masking negation logic upon negative dst register

The negation logic for the case where the off_reg is sitting in the

dst register is not correct given then we cannot just invert the add

to a sub or vice versa. As a fix, perform the final bitwise and-op

unconditionally into AX from the off_reg, then move the pointer from

the src to dst and finally use AX as the source for the original

pointer arithmetic operation such that the inversion yields a correct

result. The single non-AX mov in between is possible given constant

blinding is retaining it as it's not an immediate based operation.