On Wed, Aug 21, 2024 at 5:18 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> Check that verifier rejects BPF program containing relocation
> pointing to non-existent BTF type.
>
> To force relocation resolution on kernel side test case uses
> bpf_attr->core_relos field. This field is not exposed by libbpf,
> so directly do BPF system call in the test.
>
> Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> ---
> .../selftests/bpf/prog_tests/core_reloc_raw.c | 124 ++++++++++++++++++
> 1 file changed, 124 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c b/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c
> new file mode 100644
> index 000000000000..1ab3ab305d3b
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/core_reloc_raw.c
> @@ -0,0 +1,124 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/* Test cases that can't load programs using libbpf and need direct
> + * BPF syscall access
> + */
> +
> +#include <sys/syscall.h>
> +#include <bpf/libbpf.h>
> +#include <bpf/btf.h>
> +
> +#include "test_progs.h"
> +#include "test_btf.h"
> +#include "bpf/libbpf_internal.h"
> +
> +static char log[16 * 1024];
> +
> +/* Check that verifier rejects BPF program containing relocation
> + * pointing to non-existent BTF type.
> + */
> +static void test_bad_local_id(void)
> +{
> + struct test_btf {
> + struct btf_header hdr;
> + __u32 types[15];
> + char strings[128];
> + } raw_btf = {
> + .hdr = {
> + .magic = BTF_MAGIC,
> + .version = BTF_VERSION,
> + .hdr_len = sizeof(struct btf_header),
> + .type_off = 0,
> + .type_len = sizeof(raw_btf.types),
> + .str_off = offsetof(struct test_btf, strings) -
> + offsetof(struct test_btf, types),
> + .str_len = sizeof(raw_btf.strings),
> + },
> + .types = {
> + BTF_PTR_ENC(0), /* [1] void* */
> + BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4), /* [2] int */
> + BTF_FUNC_PROTO_ENC(2, 1), /* [3] int (*)(void*) */
> + BTF_FUNC_PROTO_ARG_ENC(8, 1),
> + BTF_FUNC_ENC(8, 3) /* [4] FUNC 'foo' type_id=2 */
> + },
> + .strings = "\0int\0 0\0foo\0"
> + };
> + __u32 log_level = 1 | 2 | 4;
> + LIBBPF_OPTS(bpf_btf_load_opts, opts,
> + .log_buf = log,
> + .log_size = sizeof(log),
> + .log_level = log_level,
> + );
> + struct bpf_insn insns[] = {
> + BPF_ALU64_IMM(BPF_MOV, BPF_REG_0, 0),
> + BPF_EXIT_INSN(),
> + };
> + struct bpf_func_info funcs[] = {
> + {
> + .insn_off = 0,
> + .type_id = 4,
> + }
> + };
> + struct bpf_core_relo relos[] = {
> + {
> + .insn_off = 0, /* patch first instruction (r0 = 0) */
> + .type_id = 100500, /* !!! this type id does not exist */
> + .access_str_off = 6, /* offset of "0" */
> + .kind = BPF_CORE_TYPE_ID_LOCAL,
> + }
> + };
> + union bpf_attr attr = {};
> + int saved_errno;
> + int prog_fd = -1;
> + int btf_fd = -1;
> +
> + btf_fd = bpf_btf_load(&raw_btf, sizeof(raw_btf), &opts);
> + saved_errno = errno;
> + if (btf_fd < 0 || env.verbosity > VERBOSE_NORMAL) {
> + printf("-------- BTF load log start --------\n");
> + printf("%s", log);
> + printf("-------- BTF load log end ----------\n");
> + }
> + if (btf_fd < 0) {
> + PRINT_FAIL("bpf_btf_load() failed, errno=%d\n", saved_errno);
> + return;
> + }
> +
> + memset(log, 0, sizeof(log));
generally speaking there is no need to memset log buffer (maybe just a
first byte, to be safe)
on the other hand, just `union bpf_attr attr = {};` is breakage
waiting to happen, I'd do memset(0) on that, we did run into problems
with that before (I believe it was systemd)
> + attr.prog_btf_fd = btf_fd;
> + attr.prog_type = BPF_TRACE_RAW_TP;
> + attr.license = (__u64)"GPL";
> + attr.insns = (__u64)&insns;
> + attr.insn_cnt = sizeof(insns) / sizeof(*insns);
> + attr.log_buf = (__u64)log;
> + attr.log_size = sizeof(log);
> + attr.log_level = log_level;
> + attr.func_info = (__u64)funcs;
> + attr.func_info_cnt = sizeof(funcs) / sizeof(*funcs);
> + attr.func_info_rec_size = sizeof(*funcs);
> + attr.core_relos = (__u64)relos;
> + attr.core_relo_cnt = sizeof(relos) / sizeof(*relos);
> + attr.core_relo_rec_size = sizeof(*relos);
I was wondering for a bit why you didn't just use bpf_prog_load(), and
it seems like it's due to core_relos fields? I don't see why we can't
extend the bpf_prog_load() API to allow to specify those. (would allow
to avoid open-coding this whole bpf_attr business, but it's fine as is
as well)
> + prog_fd = sys_bpf_prog_load(&attr, sizeof(attr), 1);
> + saved_errno = errno;
> + if (prog_fd < 0 || env.verbosity > VERBOSE_NORMAL) {
> + printf("-------- program load log start --------\n");
> + printf("%s", log);
> + printf("-------- program load log end ----------\n");
> + }
> + if (prog_fd >= 0) {
> + PRINT_FAIL("sys_bpf_prog_load() expected to fail\n");
> + goto out;
> + }
> + ASSERT_HAS_SUBSTR(log, "relo #0: bad type id 100500", "program load log");
> +
> +out:
> + close(prog_fd);
> + close(btf_fd);
> +}
> +
> +void test_core_reloc_raw(void)
> +{
> + if (test__start_subtest("bad_local_id"))
> + test_bad_local_id();
> +}
> --
> 2.45.2
>
