Re: [PATCH v14 12/12] selftests/bpf: Add verifier tests for dynamic pointers parameters in kfuncs

[Joanne Koong]

On Tue, Aug 30, 2022 at 9:22 AM Roberto Sassu
<roberto.sassu@xxxxxxxxxxxxxxx> wrote:
>
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
>
> Add verifier tests to ensure that only supported dynamic pointer types are
> accepted, that the passed argument is actually a dynamic pointer, and that
> the passed argument is a pointer to the stack.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> ---
>  .../bpf/verifier/kfunc_dynptr_param.c         | 72 +++++++++++++++++++
>  1 file changed, 72 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/verifier/kfunc_dynptr_param.c
>
> diff --git a/tools/testing/selftests/bpf/verifier/kfunc_dynptr_param.c b/tools/testing/selftests/bpf/verifier/kfunc_dynptr_param.c
> new file mode 100644
> index 000000000000..8abb8d566321
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/verifier/kfunc_dynptr_param.c
> @@ -0,0 +1,72 @@
> +{
> +       "kfunc dynamic pointer param: type not supported",
> +       .insns = {
> +       BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0),
> +       BPF_MOV64_REG(BPF_REG_6, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_6, -16),
> +       BPF_LD_MAP_FD(BPF_REG_1, 0),
> +       BPF_MOV64_IMM(BPF_REG_2, 8),
> +       BPF_MOV64_IMM(BPF_REG_3, 0),
> +       BPF_MOV64_REG(BPF_REG_4, BPF_REG_6),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_ringbuf_reserve_dynptr),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
> +       BPF_MOV64_REG(BPF_REG_2, BPF_REG_6),
> +       BPF_MOV64_IMM(BPF_REG_3, 0),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
> +       BPF_MOV64_IMM(BPF_REG_2, 0),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_ringbuf_discard_dynptr),
> +       BPF_MOV64_IMM(BPF_REG_0, 0),
> +       BPF_EXIT_INSN(),
> +       },
> +       .fixup_map_ringbuf = { 3 },
> +       .prog_type = BPF_PROG_TYPE_LSM,
> +       .kfunc = "bpf",
> +       .expected_attach_type = BPF_LSM_MAC,
> +       .flags = BPF_F_SLEEPABLE,
> +       .errstr = "arg#0 pointer type STRUCT bpf_dynptr_kern points to unsupported dynamic pointer type",
> +       .result = REJECT,
> +       .fixup_kfunc_btf_id = {
> +               { "bpf_verify_pkcs7_signature", 12 },
> +       },
> +},
> +{
> +       "kfunc dynamic pointer param: arg not a dynamic pointer",
> +       .insns = {
> +       BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8),
> +       BPF_MOV64_REG(BPF_REG_2, BPF_REG_1),
> +       BPF_MOV64_IMM(BPF_REG_3, 0),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
> +       BPF_EXIT_INSN(),
> +       },
> +       .prog_type = BPF_PROG_TYPE_LSM,
> +       .kfunc = "bpf",
> +       .expected_attach_type = BPF_LSM_MAC,
> +       .flags = BPF_F_SLEEPABLE,
> +       .errstr = "arg#0 pointer type STRUCT bpf_dynptr_kern must be valid and initialized",
> +       .result = REJECT,
> +       .fixup_kfunc_btf_id = {
> +               { "bpf_verify_pkcs7_signature", 5 },
> +       },
> +},
> +{
> +       "kfunc dynamic pointer param: arg not a pointer to stack",
> +       .insns = {
> +       BPF_MOV64_IMM(BPF_REG_1, 0),
> +       BPF_MOV64_IMM(BPF_REG_2, 0),
> +       BPF_MOV64_IMM(BPF_REG_3, 0),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, BPF_PSEUDO_KFUNC_CALL, 0, 0),
> +       BPF_EXIT_INSN(),
> +       },
> +       .prog_type = BPF_PROG_TYPE_LSM,
> +       .kfunc = "bpf",
> +       .expected_attach_type = BPF_LSM_MAC,
> +       .flags = BPF_F_SLEEPABLE,
> +       .errstr = "arg#0 pointer type STRUCT bpf_dynptr_kern not to stack",
> +       .result = REJECT,
> +       .fixup_kfunc_btf_id = {
> +               { "bpf_verify_pkcs7_signature", 3 },
> +       },
> +},

Is this logic testable in plain C BPF code? I tend to side with Andrii
[0] about finding these kinds of tests hard to maintain and read.

[0] https://lore.kernel.org/bpf/CAEf4BzZJvr+vcO57TK94GM7B5=k2wPgAub4BBJf1Uz0xNpCPVg@xxxxxxxxxxxxxx/

> --
> 2.25.1
>