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author | Alexei Starovoitov <ast@kernel.org> | 2024-01-05 07:31:34 +0300 |
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committer | Alexei Starovoitov <ast@kernel.org> | 2024-01-05 07:40:54 +0300 |
commit | 5fe4ee6ae187523f710f1b93024437a073d88b17 (patch) | |
tree | 0597b83407e92f101be92851c0b2e0eb5181b045 /tools | |
parent | 00bc8988807985e32f5103f1ac099baf593bd8a3 (diff) | |
parent | e02feb3f1f47509ec1e07b604bfbeff8c3b4e639 (diff) | |
download | linux-5fe4ee6ae187523f710f1b93024437a073d88b17.tar.xz |
Merge branch 'relax-tracing-prog-recursive-attach-rules'
Dmitrii Dolgov says:
====================
Relax tracing prog recursive attach rules
Currently, it's not allowed to attach an fentry/fexit prog to another
fentry/fexit. At the same time it's not uncommon to see a tracing
program with lots of logic in use, and the attachment limitation
prevents usage of fentry/fexit for performance analysis (e.g. with
"bpftool prog profile" command) in this case. An example could be
falcosecurity libs project that uses tp_btf tracing programs for
offloading certain part of logic into tail-called programs, but the
use-case is still generic enough -- a tracing program could be
complicated and heavy enough to warrant its profiling, yet frustratingly
it's not possible to do so use best tooling for that.
Following the corresponding discussion [1], the reason for that is to
avoid tracing progs call cycles without introducing more complex
solutions. But currently it seems impossible to load and attach tracing
programs in a way that will form such a cycle. Replace "no same type"
requirement with verification that no more than one level of attachment
nesting is allowed. In this way only one fentry/fexit program could be
attached to another fentry/fexit to cover profiling use case, and still
no cycle could be formed.
The series contains a test for recursive attachment, as well as a fix +
test for an issue in re-attachment branch of bpf_tracing_prog_attach.
When preparing the test for the main change set, I've stumbled upon the
possibility to construct a sequence of events when attach_btf would be
NULL while computing a trampoline key. It doesn't look like this issue
is triggered by the main change, because the reproduces doesn't actually
need to have an fentry attachment chain.
[1]: https://lore.kernel.org/bpf/20191108064039.2041889-16-ast@kernel.org/
====================
Link: https://lore.kernel.org/r/20240103190559.14750-1-9erthalion6@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'tools')
3 files changed, 190 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/prog_tests/recursive_attach.c b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c new file mode 100644 index 000000000000..8100509e561b --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/recursive_attach.c @@ -0,0 +1,151 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2023 Red Hat, Inc. */ +#include <test_progs.h> +#include "fentry_recursive.skel.h" +#include "fentry_recursive_target.skel.h" +#include <bpf/btf.h> +#include "bpf/libbpf_internal.h" + +/* Test recursive attachment of tracing progs with more than one nesting level + * is not possible. Create a chain of attachment, verify that the last prog + * will fail. Depending on the arguments, following cases are tested: + * + * - Recursive loading of tracing progs, without attaching (attach = false, + * detach = false). The chain looks like this: + * load target + * load fentry1 -> target + * load fentry2 -> fentry1 (fail) + * + * - Recursive attach of tracing progs (attach = true, detach = false). The + * chain looks like this: + * load target + * load fentry1 -> target + * attach fentry1 -> target + * load fentry2 -> fentry1 (fail) + * + * - Recursive attach and detach of tracing progs (attach = true, detach = + * true). This validates that attach_tracing_prog flag will be set throughout + * the whole lifecycle of an fentry prog, independently from whether it's + * detached. The chain looks like this: + * load target + * load fentry1 -> target + * attach fentry1 -> target + * detach fentry1 + * load fentry2 -> fentry1 (fail) + */ +static void test_recursive_fentry_chain(bool attach, bool detach) +{ + struct fentry_recursive_target *target_skel = NULL; + struct fentry_recursive *tracing_chain[2] = {}; + struct bpf_program *prog; + int prev_fd, err; + + target_skel = fentry_recursive_target__open_and_load(); + if (!ASSERT_OK_PTR(target_skel, "fentry_recursive_target__open_and_load")) + return; + + /* Create an attachment chain with two fentry progs */ + for (int i = 0; i < 2; i++) { + tracing_chain[i] = fentry_recursive__open(); + if (!ASSERT_OK_PTR(tracing_chain[i], "fentry_recursive__open")) + goto close_prog; + + /* The first prog in the chain is going to be attached to the target + * fentry program, the second one to the previous in the chain. + */ + prog = tracing_chain[i]->progs.recursive_attach; + if (i == 0) { + prev_fd = bpf_program__fd(target_skel->progs.test1); + err = bpf_program__set_attach_target(prog, prev_fd, "test1"); + } else { + prev_fd = bpf_program__fd(tracing_chain[i-1]->progs.recursive_attach); + err = bpf_program__set_attach_target(prog, prev_fd, "recursive_attach"); + } + + if (!ASSERT_OK(err, "bpf_program__set_attach_target")) + goto close_prog; + + err = fentry_recursive__load(tracing_chain[i]); + /* The first attach should succeed, the second fail */ + if (i == 0) { + if (!ASSERT_OK(err, "fentry_recursive__load")) + goto close_prog; + + if (attach) { + err = fentry_recursive__attach(tracing_chain[i]); + if (!ASSERT_OK(err, "fentry_recursive__attach")) + goto close_prog; + } + + if (detach) { + /* Flag attach_tracing_prog should still be set, preventing + * attachment of the following prog. + */ + fentry_recursive__detach(tracing_chain[i]); + } + } else { + if (!ASSERT_ERR(err, "fentry_recursive__load")) + goto close_prog; + } + } + +close_prog: + fentry_recursive_target__destroy(target_skel); + for (int i = 0; i < 2; i++) { + fentry_recursive__destroy(tracing_chain[i]); + } +} + +void test_recursive_fentry(void) +{ + if (test__start_subtest("attach")) + test_recursive_fentry_chain(true, false); + if (test__start_subtest("load")) + test_recursive_fentry_chain(false, false); + if (test__start_subtest("detach")) + test_recursive_fentry_chain(true, true); +} + +/* Test that a tracing prog reattachment (when we land in + * "prog->aux->dst_trampoline and tgt_prog is NULL" branch in + * bpf_tracing_prog_attach) does not lead to a crash due to missing attach_btf + */ +void test_fentry_attach_btf_presence(void) +{ + struct fentry_recursive_target *target_skel = NULL; + struct fentry_recursive *tracing_skel = NULL; + struct bpf_program *prog; + int err, link_fd, tgt_prog_fd; + + target_skel = fentry_recursive_target__open_and_load(); + if (!ASSERT_OK_PTR(target_skel, "fentry_recursive_target__open_and_load")) + goto close_prog; + + tracing_skel = fentry_recursive__open(); + if (!ASSERT_OK_PTR(tracing_skel, "fentry_recursive__open")) + goto close_prog; + + prog = tracing_skel->progs.recursive_attach; + tgt_prog_fd = bpf_program__fd(target_skel->progs.fentry_target); + err = bpf_program__set_attach_target(prog, tgt_prog_fd, "fentry_target"); + if (!ASSERT_OK(err, "bpf_program__set_attach_target")) + goto close_prog; + + err = fentry_recursive__load(tracing_skel); + if (!ASSERT_OK(err, "fentry_recursive__load")) + goto close_prog; + + tgt_prog_fd = bpf_program__fd(tracing_skel->progs.recursive_attach); + link_fd = bpf_link_create(tgt_prog_fd, 0, BPF_TRACE_FENTRY, NULL); + if (!ASSERT_GE(link_fd, 0, "link_fd")) + goto close_prog; + + fentry_recursive__detach(tracing_skel); + + err = fentry_recursive__attach(tracing_skel); + ASSERT_ERR(err, "fentry_recursive__attach"); + +close_prog: + fentry_recursive_target__destroy(target_skel); + fentry_recursive__destroy(tracing_skel); +} diff --git a/tools/testing/selftests/bpf/progs/fentry_recursive.c b/tools/testing/selftests/bpf/progs/fentry_recursive.c new file mode 100644 index 000000000000..2c9fb5ac42b2 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/fentry_recursive.c @@ -0,0 +1,14 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2023 Red Hat, Inc. */ +#include <linux/bpf.h> +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> + +char _license[] SEC("license") = "GPL"; + +/* Dummy fentry bpf prog for testing fentry attachment chains */ +SEC("fentry/XXX") +int BPF_PROG(recursive_attach, int a) +{ + return 0; +} diff --git a/tools/testing/selftests/bpf/progs/fentry_recursive_target.c b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c new file mode 100644 index 000000000000..267c876d0aba --- /dev/null +++ b/tools/testing/selftests/bpf/progs/fentry_recursive_target.c @@ -0,0 +1,25 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2023 Red Hat, Inc. */ +#include <linux/bpf.h> +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> + +char _license[] SEC("license") = "GPL"; + +/* Dummy fentry bpf prog for testing fentry attachment chains. It's going to be + * a start of the chain. + */ +SEC("fentry/bpf_testmod_fentry_test1") +int BPF_PROG(test1, int a) +{ + return 0; +} + +/* Dummy bpf prog for testing attach_btf presence when attaching an fentry + * program. + */ +SEC("raw_tp/sys_enter") +int BPF_PROG(fentry_target, struct pt_regs *regs, long id) +{ + return 0; +} |