On Thu, Feb 16, 2023 at 2:33 AM Viktor Malik <vmalik@xxxxxxxxxx> wrote:
>
> Adds a new test that tries to attach a program to fentry of two
> functions of the same name, one located in vmlinux and the other in
> bpf_testmod.
>
> To avoid conflicts with existing tests, a new function
> "bpf_fentry_shadow_test" was created both in vmlinux and in bpf_testmod.
>
> The previous commit fixed a bug which caused this test to fail. The
> verifier would always use the vmlinux function's address as the target
> trampoline address, hence trying to create two trampolines for a single
> address, which is forbidden.
>
> Signed-off-by: Viktor Malik <vmalik@xxxxxxxxxx>
> ---
> net/bpf/test_run.c | 5 +
> .../selftests/bpf/bpf_testmod/bpf_testmod.c | 6 +
> .../bpf/prog_tests/module_attach_shadow.c | 131 ++++++++++++++++++
> 3 files changed, 142 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/module_attach_shadow.c
>
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index b766a84c8536..7d46e8adbc96 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -558,6 +558,11 @@ long noinline bpf_kfunc_call_test4(signed char a, short b, int c, long d)
> return (long)a + (long)b + (long)c + d;
> }
>
> +int noinline bpf_fentry_shadow_test(int a)
> +{
> + return a + 1;
> +}
> +
> struct prog_test_member1 {
> int a;
> };
> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 46500636d8cd..c478b14fdea1 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -229,6 +229,12 @@ static const struct btf_kfunc_id_set bpf_testmod_kfunc_set = {
> .set = &bpf_testmod_check_kfunc_ids,
> };
>
> +noinline int bpf_fentry_shadow_test(int a)
> +{
> + return a + 2;
> +}
> +EXPORT_SYMBOL_GPL(bpf_fentry_shadow_test);
> +
> extern int bpf_fentry_test1(int a);
>
> static int bpf_testmod_init(void)
> diff --git a/tools/testing/selftests/bpf/prog_tests/module_attach_shadow.c b/tools/testing/selftests/bpf/prog_tests/module_attach_shadow.c
> new file mode 100644
> index 000000000000..a75d2cdde928
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/module_attach_shadow.c
> @@ -0,0 +1,131 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2022 Red Hat */
> +#include <test_progs.h>
> +#include <bpf/btf.h>
> +#include "bpf/libbpf_internal.h"
> +#include "cgroup_helpers.h"
> +
> +static const char *module_name = "bpf_testmod";
> +static const char *symbol_name = "bpf_fentry_shadow_test";
> +
> +static int get_bpf_testmod_btf_fd(void)
> +{
> + struct bpf_btf_info info;
> + char name[64];
> + __u32 id = 0, len;
> + int err, fd;
> +
> + while (true) {
> + err = bpf_btf_get_next_id(id, &id);
> + if (err) {
> + log_err("failed to iterate BTF objects");
> + return err;
> + }
> +
> + fd = bpf_btf_get_fd_by_id(id);
> + if (fd < 0) {
> + if (errno == ENOENT)
> + continue; /* expected race: BTF was unloaded */
> + err = -errno;
> + log_err("failed to get FD for BTF object #%d", id);
> + return err;
> + }
> +
> + len = sizeof(info);
> + memset(&info, 0, sizeof(info));
> + info.name = ptr_to_u64(name);
> + info.name_len = sizeof(name);
> +
> + err = bpf_obj_get_info_by_fd(fd, &info, &len);
> + if (err) {
> + err = -errno;
> + log_err("failed to get info for BTF object #%d", id);
> + close(fd);
> + return err;
> + }
> +
> + if (strcmp(name, module_name) == 0)
> + return fd;
> +
> + close(fd);
> + }
> + return -ENOENT;
> +}
> +
> +void test_module_fentry_shadow(void)
> +{
> + struct btf *vmlinux_btf = NULL, *mod_btf = NULL;
> + int err, i;
> + int btf_fd[2] = {};
> + int prog_fd[2] = {};
> + int link_fd[2] = {};
> + __s32 btf_id[2] = {};
> +
> + const struct bpf_insn trace_program[] = {
> + BPF_MOV64_IMM(BPF_REG_0, 0),
> + BPF_EXIT_INSN(),
> + };
> +
> + LIBBPF_OPTS(bpf_prog_load_opts, load_opts,
> + .expected_attach_type = BPF_TRACE_FENTRY,
> + );
nit: this is a variable declaration, so keep it together with other variables
> +
> + LIBBPF_OPTS(bpf_test_run_opts, test_opts);
> +
> + vmlinux_btf = btf__load_vmlinux_btf();
> + if (!ASSERT_OK_PTR(vmlinux_btf, "load_vmlinux_btf"))
> + return;
> +
> + btf_fd[1] = get_bpf_testmod_btf_fd();
> + if (!ASSERT_GT(btf_fd[1], 0, "get_bpf_testmod_btf_fd"))
> + goto out;
it probably won't ever happen, by FD == 0 is a valid FD, so better not
make >0 assumption here?
> +
> + mod_btf = btf_get_from_fd(btf_fd[1], vmlinux_btf);
> + if (!ASSERT_OK_PTR(mod_btf, "btf_get_from_fd"))
> + goto out;
> +
> + btf_id[0] = btf__find_by_name_kind(vmlinux_btf, symbol_name, BTF_KIND_FUNC);
> + if (!ASSERT_GT(btf_id[0], 0, "btf_find_by_name"))
> + goto out;
> +
> + btf_id[1] = btf__find_by_name_kind(mod_btf, symbol_name, BTF_KIND_FUNC);
> + if (!ASSERT_GT(btf_id[1], 0, "btf_find_by_name"))
> + goto out;
> +
> + for (i = 0; i < 2; i++) {
> + load_opts.attach_btf_id = btf_id[i];
> + load_opts.attach_btf_obj_fd = btf_fd[i];
> + prog_fd[i] = bpf_prog_load(BPF_PROG_TYPE_TRACING, NULL, "GPL",
> + trace_program,
> + sizeof(trace_program) / sizeof(struct bpf_insn),
> + &load_opts);
> + if (!ASSERT_GE(prog_fd[i], 0, "bpf_prog_load"))
> + goto out;
> +
> + // If the verifier incorrectly resolves addresses of the
> + // shadowed functions and uses the same address for both the
> + // vmlinux and the bpf_testmod functions, this will fail on
> + // attempting to create two trampolines for the same address,
> + // which is forbidden.
C++ style comments, please use /* */
> + link_fd[i] = bpf_link_create(prog_fd[i], 0, BPF_TRACE_FENTRY, NULL);
> + if (!ASSERT_GE(link_fd[i], 0, "bpf_link_create"))
> + goto out;
> + }
> +
> + err = bpf_prog_test_run_opts(prog_fd[0], &test_opts);
you don't need empty test_opts, just pass NULL
> + ASSERT_OK(err, "running test");
> +
> +out:
> + if (vmlinux_btf)
> + btf__free(vmlinux_btf);
> + if (mod_btf)
> + btf__free(mod_btf);
no need to check for non-NULL, libbpf's destructors (btf__free being
one of them) always handles NULLs correctly
> + for (i = 0; i < 2; i++) {
> + if (btf_fd[i])
> + close(btf_fd[i]);
> + if (prog_fd[i])
> + close(prog_fd[i]);
> + if (link_fd[i])
> + close(link_fd[i]);
> + }
> +}
> --
> 2.39.1
>
