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

[Gilad Reti <gilad.reti@gmail.com>]

On Tue, Jan 12, 2021 at 4:56 PM KP Singh <kpsingh@kernel.org> wrote:
>
> On Tue, Jan 12, 2021 at 10:16 AM Gilad Reti <gilad.reti@gmail.com> 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?
>

It may be possible, but from what I understood from Daniel's comment here

https://lore.kernel.org/bpf/17629073-4fab-a922-ecc3-25b019960f44@iogearbox.net/

the test should be a part of the verifier tests (which is reasonable
to me since it is
a verifier bugfix)

>
>
> > The patch was partially contibuted by CyberArk Software, Inc.
> >
> > Signed-off-by: Gilad Reti <gilad.reti@gmail.com>
> > ---
> >  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
> >