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Wed, 29 Jul 2026 06:23:11 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Wed, 29 Jul 2026 15:23:09 +0200 To: Andrey Grodzovsky Cc: bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, song@kernel.org, rostedt@goodmis.org, naveen@kernel.org, davem@davemloft.net, mhiramat@kernel.org, stable@vger.kernel.org, linux-open-source@crowdstrike.com Subject: Re: [RFC PATCH bpf-next 3/3] selftests/bpf: add ftrace_permanent test Message-ID: References: <20260729005959.3853865-1-andrey.grodzovsky@crowdstrike.com> <20260729005959.3853865-4-andrey.grodzovsky@crowdstrike.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260729005959.3853865-4-andrey.grodzovsky@crowdstrike.com> On Tue, Jul 28, 2026 at 08:59:59PM -0400, Andrey Grodzovsky wrote: > Cover the FTRACE_OPS_FL_PERMANENT fix on BPF trampolines and > ftrace-based kprobes/kretprobes: attach a fentry, fexit, kprobe, and > kretprobe program in turn and confirm kernel.ftrace_enabled=0 is > refused with EBUSY while attached, then succeeds once detached. Also > confirm a new fentry/kprobe attach is itself refused while > ftrace_enabled=0 is already in effect. > > kprobe.multi/kretprobe.multi/kprobe.session are intentionally not > covered, matching the production change's scope. > > Skip the kprobe/kretprobe subtests when CONFIG_KPROBES_ON_FTRACE is > off (e.g. arm64), read back via skel->kconfig->CONFIG_KPROBES_ON_FTRACE > (same __kconfig idiom as progs/test_fill_link_info.c). > > Assisted-by: Claude:claude-sonnet-5 > Signed-off-by: Andrey Grodzovsky > --- hi, I have some links active already after boot which makes test to fail: [root@qemu-1 bpf]# echo 0 > /proc/sys/kernel/ftrace_enabled bash: echo: write error: Device or resource busy [root@qemu-1 bpf]# ./test_progs -t ftrace_permanent -v bpf_testmod.ko is already unloaded. Loading bpf_testmod.ko... Successfully loaded bpf_testmod.ko. test_ftrace_permanent:PASS:skel_open_and_load 0 nsec check_blocks_disable:PASS:attach_fentry 0 nsec check_blocks_disable:PASS:disable_refused 0 nsec check_blocks_disable:PASS:read_back 0 nsec check_blocks_disable:PASS:still_enabled 0 nsec check_blocks_disable:FAIL:disable_after_detach unexpected error: -16 (errno 16) check_blocks_disable:PASS:reenable 0 nsec #145/1 ftrace_permanent/fentry_blocks_disable:FAIL check_blocks_disable:PASS:attach_fexit 0 nsec check_blocks_disable:PASS:disable_refused 0 nsec check_blocks_disable:PASS:read_back 0 nsec check_blocks_disable:PASS:still_enabled 0 nsec check_blocks_disable:FAIL:disable_after_detach unexpected error: -16 (errno 16) check_blocks_disable:PASS:reenable 0 nsec #145/2 ftrace_permanent/fexit_blocks_disable:FAIL check_blocks_disable:PASS:attach_kprobe 0 nsec check_blocks_disable:PASS:disable_refused 0 nsec check_blocks_disable:PASS:read_back 0 nsec check_blocks_disable:PASS:still_enabled 0 nsec check_blocks_disable:FAIL:disable_after_detach unexpected error: -16 (errno 16) check_blocks_disable:PASS:reenable 0 nsec #145/3 ftrace_permanent/kprobe_blocks_disable:FAIL check_blocks_disable:PASS:attach_kretprobe 0 nsec check_blocks_disable:PASS:disable_refused 0 nsec check_blocks_disable:PASS:read_back 0 nsec check_blocks_disable:PASS:still_enabled 0 nsec check_blocks_disable:FAIL:disable_after_detach unexpected error: -16 (errno 16) check_blocks_disable:PASS:reenable 0 nsec #145/4 ftrace_permanent/kretprobe_blocks_disable:FAIL check_attach_while_disabled_refused:FAIL:disable unexpected error: -16 (errno 16) #145/5 ftrace_permanent/fentry_attach_while_disabled_refused:FAIL check_attach_while_disabled_refused:FAIL:disable unexpected error: -16 (errno 16) #145/6 ftrace_permanent/kprobe_attach_while_disabled_refused:FAIL #145 ftrace_permanent:FAIL Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED Successfully unloaded bpf_testmod.ko. jirka > .../bpf/prog_tests/ftrace_permanent.c | 144 ++++++++++++++++++ > .../selftests/bpf/progs/ftrace_permanent.c | 43 ++++++ > 2 files changed, 187 insertions(+) > create mode 100644 tools/testing/selftests/bpf/prog_tests/ftrace_permanent.c > create mode 100644 tools/testing/selftests/bpf/progs/ftrace_permanent.c > > diff --git a/tools/testing/selftests/bpf/prog_tests/ftrace_permanent.c b/tools/testing/selftests/bpf/prog_tests/ftrace_permanent.c > new file mode 100644 > index 000000000000..dbe78009a291 > --- /dev/null > +++ b/tools/testing/selftests/bpf/prog_tests/ftrace_permanent.c > @@ -0,0 +1,144 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* Copyright (c) 2026 CrowdStrike */ > +#include > +#include "ftrace_permanent.skel.h" > + > +/* > + * fentry/fexit/kprobe/kretprobe now carry FTRACE_OPS_FL_PERMANENT, so > + * kernel.ftrace_enabled=0 must be refused with EBUSY while any of them > + * is attached, and allowed again once detached. > + * > + * kprobe.multi/kretprobe.multi/kprobe.session are out of scope. > + * kprobe/kretprobe subtests need CONFIG_KPROBES_ON_FTRACE (e.g. not on > + * arm64) and are skipped otherwise. > + */ > + > +#define FTRACE_ENABLED_PATH "/proc/sys/kernel/ftrace_enabled" > + > +static int read_ftrace_enabled(int *val) > +{ > + char buf[16] = {}; > + int fd, n; > + > + fd = open(FTRACE_ENABLED_PATH, O_RDONLY); > + if (fd < 0) > + return -errno; > + n = read(fd, buf, sizeof(buf) - 1); > + close(fd); > + if (n <= 0) > + return -EIO; > + *val = atoi(buf); > + return 0; > +} > + > +/* Returns 0 on success, or -errno on write failure. */ > +static int write_ftrace_enabled(int val) > +{ > + char buf[4]; > + int fd, n, len, err = 0; > + > + fd = open(FTRACE_ENABLED_PATH, O_WRONLY); > + if (fd < 0) > + return -errno; > + len = snprintf(buf, sizeof(buf), "%d", val); > + n = write(fd, buf, len); > + if (n < 0) > + err = -errno; > + close(fd); > + return err; > +} > + > +/* > + * Attach @prog, assert kernel.ftrace_enabled=0 is refused while attached > + * and stays at 1, then detach and assert the disable now succeeds. > + */ > +static void check_blocks_disable(struct bpf_program *prog, const char *name) > +{ > + struct bpf_link *link; > + int val, err; > + > + link = bpf_program__attach(prog); > + if (!ASSERT_OK_PTR(link, name)) > + return; > + > + err = write_ftrace_enabled(0); > + ASSERT_EQ(err, -EBUSY, "disable_refused"); > + if (!ASSERT_OK(read_ftrace_enabled(&val), "read_back")) > + goto detach; > + ASSERT_EQ(val, 1, "still_enabled"); > + > +detach: > + bpf_link__destroy(link); > + > + ASSERT_OK(write_ftrace_enabled(0), "disable_after_detach"); > + ASSERT_OK(write_ftrace_enabled(1), "reenable"); > +} > + > +/* Attach @prog while ftrace_enabled=0 and assert it is refused. */ > +static void check_attach_while_disabled_refused(struct bpf_program *prog, const char *name) > +{ > + struct bpf_link *link; > + > + if (!ASSERT_OK(write_ftrace_enabled(0), "disable")) > + return; > + > + link = bpf_program__attach(prog); > + if (!ASSERT_ERR_PTR(link, name)) > + bpf_link__destroy(link); > + > + ASSERT_OK(write_ftrace_enabled(1), "reenable"); > +} > + > +void test_ftrace_permanent(void) > +{ > + struct ftrace_permanent *skel; > + bool kprobes_on_ftrace; > + int orig = 1; > + > + /* Save and always restore ftrace_enabled. */ > + if (read_ftrace_enabled(&orig)) { > + test__skip(); > + return; > + } > + > + skel = ftrace_permanent__open_and_load(); > + if (!ASSERT_OK_PTR(skel, "skel_open_and_load")) > + goto restore; > + > + kprobes_on_ftrace = skel->kconfig->CONFIG_KPROBES_ON_FTRACE; > + > + if (test__start_subtest("fentry_blocks_disable")) > + check_blocks_disable(skel->progs.test_fentry, "attach_fentry"); > + > + if (test__start_subtest("fexit_blocks_disable")) > + check_blocks_disable(skel->progs.test_fexit, "attach_fexit"); > + > + if (test__start_subtest("kprobe_blocks_disable")) { > + if (kprobes_on_ftrace) > + check_blocks_disable(skel->progs.test_kprobe, "attach_kprobe"); > + else > + test__skip(); > + } > + > + if (test__start_subtest("kretprobe_blocks_disable")) { > + if (kprobes_on_ftrace) > + check_blocks_disable(skel->progs.test_kretprobe, "attach_kretprobe"); > + else > + test__skip(); > + } > + > + if (test__start_subtest("fentry_attach_while_disabled_refused")) > + check_attach_while_disabled_refused(skel->progs.test_fentry, "attach_fentry"); > + > + if (test__start_subtest("kprobe_attach_while_disabled_refused")) { > + if (kprobes_on_ftrace) > + check_attach_while_disabled_refused(skel->progs.test_kprobe, > + "attach_kprobe"); > + else > + test__skip(); > + } > + > + ftrace_permanent__destroy(skel); > +restore: > + write_ftrace_enabled(orig); > +} > diff --git a/tools/testing/selftests/bpf/progs/ftrace_permanent.c b/tools/testing/selftests/bpf/progs/ftrace_permanent.c > new file mode 100644 > index 000000000000..ca706d8edc23 > --- /dev/null > +++ b/tools/testing/selftests/bpf/progs/ftrace_permanent.c > @@ -0,0 +1,43 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* Copyright (c) 2026 CrowdStrike */ > +#include "vmlinux.h" > +#include > +#include > +#include > + > +char _license[] SEC("license") = "GPL"; > + > +extern bool CONFIG_KPROBES_ON_FTRACE __kconfig __weak; > + > +/* This function is here to have CONFIG_KPROBES_ON_FTRACE used and > + * added to object BTF, so the userspace side can read it back via > + * skel->kconfig->CONFIG_KPROBES_ON_FTRACE. > + */ > +int unused(void) > +{ > + return CONFIG_KPROBES_ON_FTRACE ? 0 : 1; > +} > + > +SEC("fentry/bpf_fentry_test1") > +int BPF_PROG(test_fentry, int a) > +{ > + return 0; > +} > + > +SEC("fexit/bpf_fentry_test2") > +int BPF_PROG(test_fexit, int a, __u64 b) > +{ > + return 0; > +} > + > +SEC("kprobe/bpf_fentry_test3") > +int test_kprobe(struct pt_regs *ctx) > +{ > + return 0; > +} > + > +SEC("kretprobe/bpf_fentry_test4") > +int BPF_KRETPROBE(test_kretprobe) > +{ > + return 0; > +} > -- > 2.34.1 >