Re: [PATCH bpf-next v3 5/5] selftests: bpf: test writable buffers in raw tps

Matt Mullins
2019-04-22T19:28:01Z

On Mon, 2019-04-22 at 18:32 +0000, Yonghong Song wrote:
>
> On 4/19/19 2:04 PM, Matt Mullins wrote:
> > This tests that:
> > * a BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE cannot be attached if it
> > uses either:
> > * a variable offset to the tracepoint buffer, or
> > * an offset beyond the size of the tracepoint buffer
> > * a tracer can modify the buffer provided when attached to a writable
> > tracepoint in bpf_prog_test_run
> >
> > Signed-off-by: Matt Mullins <mmullins@fb.com>
> > ---
> > include/trace/events/bpf_test_run.h | 50 ++++++++++++
> > net/bpf/test_run.c | 4 +
> > .../raw_tp_writable_reject_nbd_invalid.c | 40 ++++++++++
> > .../bpf/prog_tests/raw_tp_writable_test_run.c | 80 +++++++++++++++++++
> > .../selftests/bpf/verifier/raw_tp_writable.c | 34 ++++++++
> > 5 files changed, 208 insertions(+)
> > create mode 100644 include/trace/events/bpf_test_run.h
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/raw_tp_writable_reject_nbd_invalid.c
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/raw_tp_writable_test_run.c
> > create mode 100644 tools/testing/selftests/bpf/verifier/raw_tp_writable.c
> >
> > diff --git a/include/trace/events/bpf_test_run.h b/include/trace/events/bpf_test_run.h
> > new file mode 100644
> > index 000000000000..abf466839ea4
> > --- /dev/null
> > +++ b/include/trace/events/bpf_test_run.h
> > @@ -0,0 +1,50 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#undef TRACE_SYSTEM
> > +#define TRACE_SYSTEM bpf_test_run
> > +
> > +#if !defined(_TRACE_NBD_H) || defined(TRACE_HEADER_MULTI_READ)
> > +#define _TRACE_BPF_TEST_RUN_H
> > +
> > +#include <linux/tracepoint.h>
> > +
> > +DECLARE_EVENT_CLASS(bpf_test_finish,
> > +
> > + TP_PROTO(int *err),
> > +
> > + TP_ARGS(err),
> > +
> > + TP_STRUCT__entry(
> > + __field(int, err)
> > + ),
> > +
> > + TP_fast_assign(
> > + __entry->err = *err;
> > + ),
> > +
> > + TP_printk("bpf_test_finish with err=%d", __entry->err)
> > +);
> > +
> > +#ifdef DEFINE_EVENT_WRITABLE
> > +#undef BPF_TEST_RUN_DEFINE_EVENT
> > +#define BPF_TEST_RUN_DEFINE_EVENT(template, call, proto, args, size) \
> > + DEFINE_EVENT_WRITABLE(template, call, PARAMS(proto), \
> > + PARAMS(args), size)
> > +#else
> > +#undef BPF_TEST_RUN_DEFINE_EVENT
> > +#define BPF_TEST_RUN_DEFINE_EVENT(template, call, proto, args, size) \
> > + DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args))
> > +#endif
> > +
> > +BPF_TEST_RUN_DEFINE_EVENT(bpf_test_finish, bpf_test_finish,
> > +
> > + TP_PROTO(int *err),
> > +
> > + TP_ARGS(err),
> > +
> > + sizeof(int)
> > +);
> > +
> > +#endif
> > +
> > +/* This part must be outside protection */
> > +#include <trace/define_trace.h>
> > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> > index fab142b796ef..25e757102595 100644
> > --- a/net/bpf/test_run.c
> > +++ b/net/bpf/test_run.c
> > @@ -13,6 +13,9 @@
> > #include <net/sock.h>
> > #include <net/tcp.h>
> >
> > +#define CREATE_TRACE_POINTS
> > +#include <trace/events/bpf_test_run.h>
> > +
> > static int bpf_test_run(struct bpf_prog *prog, void *ctx, u32 repeat,
> > u32 *retval, u32 *time)
> > {
> > @@ -100,6 +103,7 @@ static int bpf_test_finish(const union bpf_attr *kattr,
> > if (err != -ENOSPC)
> > err = 0;
> > out:
> > + trace_bpf_test_finish(&err);
> > return err;
> > }
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/raw_tp_writable_reject_nbd_invalid.c b/tools/testing/selftests/bpf/prog_tests/raw_tp_writable_reject_nbd_invalid.c
> > new file mode 100644
> > index 000000000000..328d5c4b084b
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/raw_tp_writable_reject_nbd_invalid.c
> > @@ -0,0 +1,40 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <test_progs.h>
> > +#include <linux/nbd.h>
> > +
> > +void test_raw_tp_writable_reject_nbd_invalid(void)
> > +{
> > + __u32 duration = 0;
> > + char error[4096];
> > + int bpf_fd = -1, tp_fd = -1;
> > +
> > + const struct bpf_insn program[] = {
> > + /* r6 is our tp buffer */
> > + BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, 0),
> > + BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_6, 128),
>
> The number "128" is a little cryptic. Maybe you can use something like
> sizeof(struct nbd_request)?

That was explicitly chosen to be (far) larger than an nbd_request, as
this program should be rejected by the verifier. If you really want, I
can do `sizeof(struct nbd_request) + some constant` and add a comment.
But the size of an nbd request should never change, as that's a network
protocol.

>
> > + BPF_EXIT_INSN(),
> > + };
> > +
> > + struct bpf_load_program_attr load_attr = {
> > + .prog_type = BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE,
> > + .license = "GPL v2",
> > + .insns = program,
> > + .insns_cnt = sizeof(program) / sizeof(struct bpf_insn),
> > + .log_level = 2,
> > + };
> > +
> > + bpf_fd = bpf_load_program_xattr(&load_attr, error, sizeof(error));
> > + if (CHECK(bpf_fd < 0, "bpf_raw_tracepoint_writable loaded",
> > + "failed: %d errno %d\n", bpf_fd, errno))
> > + return;
> > +
> > + tp_fd = bpf_raw_tracepoint_open("nbd_send_request", bpf_fd);
> > + if (CHECK(tp_fd >= 0, "bpf_raw_tracepoint_writable opened",
> > + "erroneously succeeded\n"))
> > + goto out_bpffd;
> > +
> > + close(tp_fd);
> > +out_bpffd:
> > + close(bpf_fd);
> > +}
> > diff --git a/tools/testing/selftests/bpf/prog_tests/raw_tp_writable_test_run.c b/tools/testing/selftests/bpf/prog_tests/raw_tp_writable_test_run.c
> > new file mode 100644
> > index 000000000000..4145925f9cab
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/raw_tp_writable_test_run.c
> > @@ -0,0 +1,80 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <test_progs.h>
> > +#include <linux/nbd.h>
> > +
> > +void test_raw_tp_writable_test_run(void)
> > +{
> > + __u32 duration = 0;
> > + char error[4096];
> > +
> > + const struct bpf_insn trace_program[] = {
> > + BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, 0),
> > + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_6, 0),
> > + BPF_LD_IMM64(BPF_REG_0, 42),
>
> You can use BPF_MOV64_IMM(BPF_REG_0, 42) instead of BPF_LD_IMM64.
> BPF_LD_IMM64 is fine, but probably BPF_MOV64_IMM is better.
> The same for a few below instances.

Ah, right. I don't need the second opcode if the value can be zero-
extended.

>
> > + BPF_STX_MEM(BPF_W, BPF_REG_6, BPF_REG_0, 0),
> > + BPF_EXIT_INSN(),
> > + };
> > +
> > + struct bpf_load_program_attr load_attr = {
> > + .prog_type = BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE,
> > + .license = "GPL v2",
> > + .insns = trace_program,
> > + .insns_cnt = sizeof(trace_program) / sizeof(struct bpf_insn),
> > + .log_level = 2,
> > + };
> > +
> > + int bpf_fd = bpf_load_program_xattr(&load_attr, error, sizeof(error));
> > + if (CHECK(bpf_fd < 0, "bpf_raw_tracepoint_writable loaded",
> > + "failed: %d errno %d\n", bpf_fd, errno))
> > + return;
> > +
> > + const struct bpf_insn skb_program[] = {
> > + BPF_LD_IMM64(BPF_REG_0, 0),
> > + BPF_EXIT_INSN(),
> > + };
> > +
> > + struct bpf_load_program_attr skb_load_attr = {
> > + .prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
> > + .license = "GPL v2",
> > + .insns = skb_program,
> > + .insns_cnt = sizeof(skb_program) / sizeof(struct bpf_insn),
> > + };
> > +
> > + int filter_fd =
> > + bpf_load_program_xattr(&skb_load_attr, error, sizeof(error));
> > + if (CHECK(filter_fd < 0, "test_program_loaded", "failed: %d errno %d\n",
> > + filter_fd, errno))
> > + goto out_bpffd;
> > +
> > + int tp_fd = bpf_raw_tracepoint_open("bpf_test_finish", bpf_fd);
> > + if (CHECK(tp_fd < 0, "bpf_raw_tracepoint_writable opened",
> > + "failed: %d errno %d\n", tp_fd, errno))
> > + goto out_filterfd;
> > +
> > + char test_skb[128] = {
> > + 0,
> > + };
> > +
> > + __u32 prog_ret;
> > + int err = bpf_prog_test_run(filter_fd, 1, test_skb, sizeof(test_skb), 0,
> > + 0, &prog_ret, 0);
> > + CHECK(err != 42, "test_run",
> > + "tracepoint did not modify return value\n");
> > + CHECK(prog_ret != 0, "test_run_ret",
> > + "socket_filter did not return 0\n");
> > +
> > + close(tp_fd);
> > +
> > + err = bpf_prog_test_run(filter_fd, 1, test_skb, sizeof(test_skb), 0, 0,
> > + &prog_ret, 0);
> > + CHECK(err != 0, "test_run_notrace",
> > + "test_run failed with %d errno %d\n", err, errno);
> > + CHECK(prog_ret != 0, "test_run_ret_notrace",
> > + "socket_filter did not return 0\n");
> > +
> > +out_filterfd:
> > + close(filter_fd);
> > +out_bpffd:
> > + close(bpf_fd);
> > +}
> > diff --git a/tools/testing/selftests/bpf/verifier/raw_tp_writable.c b/tools/testing/selftests/bpf/verifier/raw_tp_writable.c
> > new file mode 100644
> > index 000000000000..95b5d70a1dc1
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/verifier/raw_tp_writable.c
> > @@ -0,0 +1,34 @@
> > +{
> > + "raw_tracepoint_writable: reject variable offset",
> > + .insns = {
> > + /* r6 is our tp buffer */
> > + BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, 0),
> > +
> > + BPF_LD_MAP_FD(BPF_REG_1, 0),
> > + /* move the key (== 0) to r10-8 */
> > + BPF_MOV32_IMM(BPF_REG_0, 0),
> > + BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> > + BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> > + BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_0, 0),
> > + /* lookup in the map */
> > + BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
> > + BPF_FUNC_map_lookup_elem),
> > +
> > + /* exit clean if null */
> > + BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
> > + BPF_EXIT_INSN(),
> > +
> > + /* shift the buffer pointer to a variable location */
> > + BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0),
> > + BPF_ALU64_REG(BPF_ADD, BPF_REG_6, BPF_REG_0),
> > + /* clobber whatever's there */
> > + BPF_MOV64_IMM(BPF_REG_7, 4242),
> > + BPF_STX_MEM(BPF_DW, BPF_REG_6, BPF_REG_7, 0),
> > +
> > + BPF_MOV64_IMM(BPF_REG_0, 0),
> > + BPF_EXIT_INSN(),
> > + },
> > + .fixup_map_hash_8b = { 1, },
> > + .prog_type = BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE,
> > + .errstr = "R6 invalid variable buffer offset: off=0, var_off=(0x0; 0xffffffff)",
> > +},
> >