Currently, for BPF_JEQ/BPF_JNE insn, verifier determines
whether the branch is taken or not only if both operands
are constants. Therefore, for the following code snippet,
  0: (85) call bpf_ktime_get_ns#5       ; R0_w=scalar()
  1: (a5) if r0 < 0x3 goto pc+2         ; R0_w=scalar(umin=3)
  2: (b7) r2 = 2                        ; R2_w=2
  3: (1d) if r0 == r2 goto pc+2 6

At insn 3, since r0 is not a constant, verifier assumes both branch
can be taken which may lead inproper verification failure.

Add comparing umin/umax value and the constant. If the umin value
is greater than the constant, or umax value is smaller than the constant,
for JEQ the branch must be not-taken, and for JNE the branch must be taken.
The jmp32 mode JEQ/JNE branch taken checking is also handled similarly.

The following lists the veristat result w.r.t. changed number
of processes insns during verification:

File                                                   Program                                               Insns (A)  Insns (B)  Insns    (DIFF)
-----------------------------------------------------  ----------------------------------------------------  ---------  ---------  ---------------
test_cls_redirect.bpf.linked3.o                        cls_redirect                                              64980      73472  +8492 (+13.07%)
test_seg6_loop.bpf.linked3.o                           __add_egr_x                                               12425      12423      -2 (-0.02%)
test_tcp_hdr_options.bpf.linked3.o                     estab                                                      2634       2558     -76 (-2.89%)
test_parse_tcp_hdr_opt.bpf.linked3.o                   xdp_ingress_v6                                             1421       1420      -1 (-0.07%)
test_parse_tcp_hdr_opt_dynptr.bpf.linked3.o            xdp_ingress_v6                                             1238       1237      -1 (-0.08%)
test_tc_dtime.bpf.linked3.o                            egress_fwdns_prio100                                        414        411      -3 (-0.72%)

Mostly a small improvement but test_cls_redirect.bpf.linked3.o has a 13% regression.
I checked with verifier log and found it this is due to pruning.
For some JEQ/JNE branches impacted by this patch,
one branch is explored and the other has state equivalence and
pruned.
Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230406164455.1045294-1-yhs@fb.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>