On Sat, Feb 6, 2021 at 5:11 PM Andrei Matei <andreimatei1@xxxxxxxxx> wrote:
>
> Add a higher-level test (C BPF program) for the new functionality -
> variable access stack reads and writes.
>
> Signed-off-by: Andrei Matei <andreimatei1@xxxxxxxxx>
> ---
> .../selftests/bpf/prog_tests/stack_var_off.c | 36 ++++++++++++
> .../selftests/bpf/progs/test_stack_var_off.c | 56 +++++++++++++++++++
> 2 files changed, 92 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/stack_var_off.c
> create mode 100644 tools/testing/selftests/bpf/progs/test_stack_var_off.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/stack_var_off.c b/tools/testing/selftests/bpf/prog_tests/stack_var_off.c
> new file mode 100644
> index 000000000000..52e00486b1aa
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/stack_var_off.c
> @@ -0,0 +1,36 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <test_progs.h>
> +#include "test_stack_var_off.skel.h"
> +
> +/* Test read and writes to the stack performed with offsets that are not
> + * statically known.
> + */
> +void test_stack_var_off(void)
> +{
> + int duration = 0;
> + struct test_stack_var_off *skel;
> +
> + skel = test_stack_var_off__open_and_load();
> + if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
> + return;
> + if (CHECK(!skel->bss, "check_bss", ".bss wasn't mmap()-ed\n"))
> + goto cleanup;
can't happen, no need to check for !skel->bss
> +
> + test_stack_var_off__attach(skel);
check errors (ASSERT_OK is good for this)
> +
> + /* Give pid to bpf prog so it doesn't trigger for anyone else. */
> + skel->bss->test_pid = getpid();
> + /* Initialize the probe's input. */
> + skel->bss->input[0] = 2;
> + skel->bss->input[1] = 42; /* This will be returned in probe_res. */
> +
> + /* Trigger probe. */
> + usleep(1);
> +
> + if (CHECK(skel->bss->probe_res != 42, "check_probe_res",
> + "wrong probe res: %d\n", skel->bss->probe_res))
> + goto cleanup;
> +
> +cleanup:
> + test_stack_var_off__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_stack_var_off.c b/tools/testing/selftests/bpf/progs/test_stack_var_off.c
> new file mode 100644
> index 000000000000..bd9c8d86cd91
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_stack_var_off.c
> @@ -0,0 +1,56 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (c) 2017 Facebook
2021 already :) Facebook isn't right here as well, probably?
> +
> +#include <linux/ptrace.h>
don't need this
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
and don't need this as well
> +
> +int probe_res;
> +
> +char input[4] = {};
> +int test_pid;
> +
> +SEC("tracepoint/syscalls/sys_enter_nanosleep")
> +int probe(void *ctx)
> +{
> + /* This BPF program performs variable-offset reads and writes on a
> + * stack-allocated buffer.
> + */
> + char stack_buf[16];
> + unsigned long len;
> + unsigned long last;
> +
> + if (test_pid == 0)
> + return 0;
can't happen, please remove
> + if ((bpf_get_current_pid_tgid() >> 32) != test_pid)
> + return 0;
> +
> + /* Copy the input to the stack. */
> + __builtin_memcpy(stack_buf, input, 4);
> +
> + /* The first byte in the buffer indicates the length. */
> + len = stack_buf[0] & 0xf;
> + last = (len - 1) & 0xf;
> +
> + /* Append something to the buffer. The offset where we write is not
> + * statically known; this is a variable-offset stack write.
> + */
> + stack_buf[len] = 42;
> +
> + /* Index into the buffer at an unknown offset. This is a
> + * variable-offset stack read.
> + *
> + * Note that if it wasn't for the preceding variable-offset write, this
> + * read would be rejected because the stack slot cannot be verified as
> + * being initialized. With the preceding variable-offset write, the
> + * stack slot still cannot be verified, but the write inhibits the
> + * respective check on the reasoning that, if there was a
> + * variable-offset to a higher-or-equal spot, we're probably reading
> + * what we just wrote.
> + */
> + probe_res = stack_buf[last];
> + return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.27.0
>
