Alignment check in tnum_is_aligned()

[Bogdan Harjoc <harjoc@xxxxxxxxx>]

Hello,

bpf programs that call lock_xadd() on pointers obtained from bpf
helpers fail to load because tnum_is_aligned() returns false during
bpf validation. Should tnum_is_aligned() evaluate a.value & a.mask
instead of a.value | a.mask ?

An example bpf tracing snippet that fails validation is:

    struct task_struct *t = (struct task_struct *)bpf_get_current_task();
    lock_xadd(&t->usage.refs.counter, 1);

I noticed using a kprobe (listed below) that tnum_is_aligned()
receives value=0, mask=0xffffffffffffffff and returns 0 for the
lock_xadd() call above.

=====
b = BPF(text=R"""
#include <uapi/linux/ptrace.h>
int in_tnum_is_aligned(struct pt_regs *regs) {
    bpf_trace_printk("in value=%llx mask=%llx\n", regs->di, regs->si);
    return 0;
}
int out_tnum_is_aligned(struct pt_regs *regs) {
    bpf_trace_printk("out aligned=%llx\n", regs->ax);
    return 0;
}
""")

b.attach_kprobe(event="tnum_is_aligned", fn_name="in_fn")
b.attach_kretprobe(event="tnum_is_aligned", fn_name="out_fn")
b.trace_print(fmt="{1} {5}")
=====

Cheers!