Re: [PATCH bpf-next] selftests/bpf: Remove two infinite loop bound check cases

[Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx>]

On 3/28/2023 2:55 AM, Andrii Nakryiko wrote:
> On Sun, Mar 26, 2023 at 11:21 PM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote:
> > On 3/27/2023 11:20 AM, Andrii Nakryiko wrote:
> > > On Sun, Mar 26, 2023 at 7:45 PM Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> wrote:
> > > > From: Xu Kuohai <xukuohai@xxxxxxxxxx>
> > > >
> > > > The two infinite loop bound check cases added by commit
> > > > 1a3148fc171f ("selftests/bpf: Check when bounds are not in the 32-bit range")
> > > > take a long time to execute but don't add much value.
> > > >
> > > > Remove them to reduce run time of test_verifier.
> > >
> > > Summary: 2042 PASSED, 0 SKIPPED, 1 FAILED
> > >
> > > real    0m4.780s
> > > user    0m0.458s
> > > sys     0m3.871s
> > >
> > >
> > > 5 seconds isn't such a long time, especially when we compare it to
> > > test_progs (even with parallelization).
> >
> > Well, I actually don't know if it is "long time".
> >
> > This patch was sent to address Alexei's concern about the run time
> > of test_verifier in mail [1].
>
>    > These infinite loops don't add much value to the actual test.
>    > Please rewrite them without infinite loops.
>
> Alexei asked to improve the test, not to just remove it, if I
> understand correctly. If the test is there, presumably it's useful. If
> it can be implemented better, let's do that. Just removing the test
> seems like a wrong move.

OK. I added upper bounds to the two loops to make them finite.

> > [1] https://lore.kernel.org/bpf/20230322213056.2470-1-daniel@xxxxxxxxxxxxx/T/#mb3d6363a693ccd63d416d9d787db17f8fdcb8442
> >
> > > > Fixes: 1a3148fc171f ("selftests/bpf: Check when bounds are not in the 32-bit range")
> > > > Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
> > > > ---
> > > >    tools/testing/selftests/bpf/verifier/bounds.c | 50 -------------------
> > > >    1 file changed, 50 deletions(-)
> > > >
> > > > diff --git a/tools/testing/selftests/bpf/verifier/bounds.c b/tools/testing/selftests/bpf/verifier/bounds.c
> > > > index 74b1917d4208..515a8222f08f 100644
> > > > --- a/tools/testing/selftests/bpf/verifier/bounds.c
> > > > +++ b/tools/testing/selftests/bpf/verifier/bounds.c
> > > > @@ -777,31 +777,6 @@
> > > >           .result = ACCEPT,
> > > >           .prog_type = BPF_PROG_TYPE_XDP,
> > > >    },
> > > > -{
> > > > -       "bound check with JMP_JSLT for crossing 64-bit signed boundary",
> > > > -       .insns = {
> > > > -       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, offsetof(struct xdp_md, data)),
> > > > -       BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1, offsetof(struct xdp_md, data_end)),
> > > > -       BPF_MOV64_REG(BPF_REG_1, BPF_REG_2),
> > > > -       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 1),
> > > > -       BPF_JMP_REG(BPF_JGT, BPF_REG_1, BPF_REG_3, 8),
> > > > -
> > > > -       BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_2, 0),
> > > > -       BPF_LD_IMM64(BPF_REG_0, 0x7fffffffffffff10),
> > > > -       BPF_ALU64_REG(BPF_ADD, BPF_REG_1, BPF_REG_0),
> > > > -
> > > > -       BPF_LD_IMM64(BPF_REG_0, 0x8000000000000000),
> > > > -       BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 1),
> > > > -       /* r1 signed range is [S64_MIN, S64_MAX] */
> > > > -       BPF_JMP_REG(BPF_JSLT, BPF_REG_0, BPF_REG_1, -2),
> > > > -
> > > > -       BPF_MOV64_IMM(BPF_REG_0, 0),
> > > > -       BPF_EXIT_INSN(),
> > > > -       },
> > > > -       .errstr = "BPF program is too large",
> > > > -       .result = REJECT,
> > > > -       .prog_type = BPF_PROG_TYPE_XDP,
> > > > -},
> > > >    {
> > > >           "bound check for loop upper bound greater than U32_MAX",
> > > >           .insns = {
> > > > @@ -849,28 +824,3 @@
> > > >           .result = ACCEPT,
> > > >           .prog_type = BPF_PROG_TYPE_XDP,
> > > >    },
> > > > -{
> > > > -       "bound check with JMP32_JSLT for crossing 32-bit signed boundary",
> > > > -       .insns = {
> > > > -       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, offsetof(struct xdp_md, data)),
> > > > -       BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1, offsetof(struct xdp_md, data_end)),
> > > > -       BPF_MOV64_REG(BPF_REG_1, BPF_REG_2),
> > > > -       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 1),
> > > > -       BPF_JMP_REG(BPF_JGT, BPF_REG_1, BPF_REG_3, 6),
> > > > -
> > > > -       BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_2, 0),
> > > > -       BPF_MOV32_IMM(BPF_REG_0, 0x7fffff10),
> > > > -       BPF_ALU32_REG(BPF_ADD, BPF_REG_1, BPF_REG_0),
> > > > -
> > > > -       BPF_MOV32_IMM(BPF_REG_0, 0x80000000),
> > > > -       BPF_ALU32_IMM(BPF_ADD, BPF_REG_0, 1),
> > > > -       /* r1 signed range is [S32_MIN, S32_MAX] */
> > > > -       BPF_JMP32_REG(BPF_JSLT, BPF_REG_0, BPF_REG_1, -2),
> > > > -
> > > > -       BPF_MOV64_IMM(BPF_REG_0, 0),
> > > > -       BPF_EXIT_INSN(),
> > > > -       },
> > > > -       .errstr = "BPF program is too large",
> > > > -       .result = REJECT,
> > > > -       .prog_type = BPF_PROG_TYPE_XDP,
> > > > -},
> > > > --
> > > > 2.30.2
> > > .
> .