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author | Alan Maguire <alan.maguire@oracle.com> | 2021-11-05 19:50:46 +0300 |
---|---|---|
committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-11-09 00:17:55 +0300 |
commit | c23551c9c36ae394f9c53a5adf1944a943c65e0b (patch) | |
tree | 471a3ccfe813414650448557d08ac6380db24eca /tools | |
parent | b89ddf4cca43f1269093942cf5c4e457fd45c335 (diff) | |
download | linux-c23551c9c36ae394f9c53a5adf1944a943c65e0b.tar.xz |
selftests/bpf: Add exception handling selftests for tp_bpf program
Exception handling is triggered in BPF tracing programs when a NULL pointer
is dereferenced; the exception handler zeroes the target register and
execution of the BPF program progresses.
To test exception handling then, we need to trigger a NULL pointer dereference
for a field which should never be zero; if it is, the only explanation is the
exception handler ran. task->task_works is the NULL pointer chosen (for a new
task from fork() no work is associated), and the task_works->func field should
not be zero if task_works is non-NULL. The test verifies that task_works and
task_works->func are 0.
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1636131046-5982-3-git-send-email-alan.maguire@oracle.com
Diffstat (limited to 'tools')
-rw-r--r-- | tools/testing/selftests/bpf/prog_tests/exhandler.c | 43 | ||||
-rw-r--r-- | tools/testing/selftests/bpf/progs/exhandler_kern.c | 43 |
2 files changed, 86 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/prog_tests/exhandler.c b/tools/testing/selftests/bpf/prog_tests/exhandler.c new file mode 100644 index 000000000000..118bb182ee20 --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/exhandler.c @@ -0,0 +1,43 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2021, Oracle and/or its affiliates. */ + +#include <test_progs.h> + +/* Test that verifies exception handling is working. fork() + * triggers task_newtask tracepoint; that new task will have a + * NULL pointer task_works, and the associated task->task_works->func + * should not be NULL if task_works itself is non-NULL. + * + * So to verify exception handling we want to see a NULL task_works + * and task_works->func; if we see this we can conclude that the + * exception handler ran when we attempted to dereference task->task_works + * and zeroed the destination register. + */ +#include "exhandler_kern.skel.h" + +void test_exhandler(void) +{ + int err = 0, duration = 0, status; + struct exhandler_kern *skel; + pid_t cpid; + + skel = exhandler_kern__open_and_load(); + if (CHECK(!skel, "skel_load", "skeleton failed: %d\n", err)) + goto cleanup; + + skel->bss->test_pid = getpid(); + + err = exhandler_kern__attach(skel); + if (!ASSERT_OK(err, "attach")) + goto cleanup; + cpid = fork(); + if (!ASSERT_GT(cpid, -1, "fork failed")) + goto cleanup; + if (cpid == 0) + _exit(0); + waitpid(cpid, &status, 0); + + ASSERT_NEQ(skel->bss->exception_triggered, 0, "verify exceptions occurred"); +cleanup: + exhandler_kern__destroy(skel); +} diff --git a/tools/testing/selftests/bpf/progs/exhandler_kern.c b/tools/testing/selftests/bpf/progs/exhandler_kern.c new file mode 100644 index 000000000000..f5ca142abf8f --- /dev/null +++ b/tools/testing/selftests/bpf/progs/exhandler_kern.c @@ -0,0 +1,43 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2021, Oracle and/or its affiliates. */ + +#include "vmlinux.h" + +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> +#include <bpf/bpf_core_read.h> + +char _license[] SEC("license") = "GPL"; + +unsigned int exception_triggered; +int test_pid; + +/* TRACE_EVENT(task_newtask, + * TP_PROTO(struct task_struct *p, u64 clone_flags) + */ +SEC("tp_btf/task_newtask") +int BPF_PROG(trace_task_newtask, struct task_struct *task, u64 clone_flags) +{ + int pid = bpf_get_current_pid_tgid() >> 32; + struct callback_head *work; + void *func; + + if (test_pid != pid) + return 0; + + /* To verify we hit an exception we dereference task->task_works->func. + * If task work has been added, + * - task->task_works is non-NULL; and + * - task->task_works->func is non-NULL also (the callback function + * must be specified for the task work. + * + * However, for a newly-created task, task->task_works is NULLed, + * so we know the exception handler triggered if task_works is + * NULL and func is NULL. + */ + work = task->task_works; + func = work->func; + if (!work && !func) + exception_triggered++; + return 0; +} |