Re: [PATCH 2/2] selftests/bpf: add verifier test for PTR_TO_MEM spill

[KP Singh]

On Tue, Jan 12, 2021 at 10:16 AM Gilad Reti <gilad.reti@xxxxxxxxx> wrote:
>
> Add test to check that the verifier is able to recognize spilling of
> PTR_TO_MEM registers.
>

It would be nice to have some explanation of what the test does to
recognize the spilling of the PTR_TO_MEM registers in the commit
log as well.

Would it be possible to augment an existing test_progs
program like tools/testing/selftests/bpf/progs/test_ringbuf.c to test
this functionality?



> The patch was partially contibuted by CyberArk Software, Inc.
>
> Signed-off-by: Gilad Reti <gilad.reti@xxxxxxxxx>
> ---
>  tools/testing/selftests/bpf/test_verifier.c   | 12 +++++++-
>  .../selftests/bpf/verifier/spill_fill.c       | 30 +++++++++++++++++++
>  2 files changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index 777a81404fdb..f8569f04064b 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -50,7 +50,7 @@
>  #define MAX_INSNS      BPF_MAXINSNS
>  #define MAX_TEST_INSNS 1000000
>  #define MAX_FIXUPS     8
> -#define MAX_NR_MAPS    20
> +#define MAX_NR_MAPS    21
>  #define MAX_TEST_RUNS  8
>  #define POINTER_VALUE  0xcafe4all
>  #define TEST_DATA_LEN  64
> @@ -87,6 +87,7 @@ struct bpf_test {
>         int fixup_sk_storage_map[MAX_FIXUPS];
>         int fixup_map_event_output[MAX_FIXUPS];
>         int fixup_map_reuseport_array[MAX_FIXUPS];
> +       int fixup_map_ringbuf[MAX_FIXUPS];
>         const char *errstr;
>         const char *errstr_unpriv;
>         uint32_t insn_processed;
> @@ -640,6 +641,7 @@ static void do_test_fixup(struct bpf_test *test, enum bpf_prog_type prog_type,
>         int *fixup_sk_storage_map = test->fixup_sk_storage_map;
>         int *fixup_map_event_output = test->fixup_map_event_output;
>         int *fixup_map_reuseport_array = test->fixup_map_reuseport_array;
> +       int *fixup_map_ringbuf = test->fixup_map_ringbuf;
>
>         if (test->fill_helper) {
>                 test->fill_insns = calloc(MAX_TEST_INSNS, sizeof(struct bpf_insn));
> @@ -817,6 +819,14 @@ static void do_test_fixup(struct bpf_test *test, enum bpf_prog_type prog_type,
>                         fixup_map_reuseport_array++;
>                 } while (*fixup_map_reuseport_array);
>         }
> +       if (*fixup_map_ringbuf) {
> +               map_fds[20] = create_map(BPF_MAP_TYPE_RINGBUF, 0,
> +                                          0, 4096);
> +               do {
> +                       prog[*fixup_map_ringbuf].imm = map_fds[20];
> +                       fixup_map_ringbuf++;
> +               } while (*fixup_map_ringbuf);
> +       }
>  }
>
>  struct libcap {
> diff --git a/tools/testing/selftests/bpf/verifier/spill_fill.c b/tools/testing/selftests/bpf/verifier/spill_fill.c
> index 45d43bf82f26..1833b6c730dd 100644
> --- a/tools/testing/selftests/bpf/verifier/spill_fill.c
> +++ b/tools/testing/selftests/bpf/verifier/spill_fill.c
> @@ -28,6 +28,36 @@
>         .result = ACCEPT,
>         .result_unpriv = ACCEPT,
>  },
> +{
> +       "check valid spill/fill, ptr to mem",
> +       .insns = {
> +       /* reserve 8 byte ringbuf memory */
> +       BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
> +       BPF_LD_MAP_FD(BPF_REG_1, 0),
> +       BPF_MOV64_IMM(BPF_REG_2, 8),
> +       BPF_MOV64_IMM(BPF_REG_3, 0),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_ringbuf_reserve),
> +       /* store a pointer to the reserved memory in R6 */
> +       BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
> +       /* check whether the reservation was successful */
> +       BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 6),
> +       /* spill R6(mem) into the stack */
> +       BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_6, -8),
> +       /* fill it back in R7 */
> +       BPF_LDX_MEM(BPF_DW, BPF_REG_7, BPF_REG_10, -8),
> +       /* should be able to access *(R7) = 0 */
> +       BPF_ST_MEM(BPF_DW, BPF_REG_7, 0, 0),
> +       /* submit the reserved rungbuf memory */
> +       BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
> +       BPF_MOV64_IMM(BPF_REG_2, 0),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_ringbuf_submit),
> +       BPF_MOV64_IMM(BPF_REG_0, 0),
> +       BPF_EXIT_INSN(),
> +       },
> +       .fixup_map_ringbuf = { 1 },
> +       .result = ACCEPT,
> +       .result_unpriv = ACCEPT,
> +},
>  {
>         "check corrupted spill/fill",
>         .insns = {
> --
> 2.27.0
>