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    Subject[PATCH 28/85] perf augmented_raw_syscalls: Change helper to consider just the augmented_filename part
    Date
    From: Arnaldo Carvalho de Melo <acme@redhat.com>

    So that we can use it for multiple args, baby steps not to step into the
    verifier toes.

    In the process make sure we handle -EFAULT from bpf_prog_read_str(), as
    this really is needed now that we'll handle more than one augmented
    argument, i.e. if there is failure, then we have the argument that fails
    have:

    (size = 0, err = -EFAULT, value = [] )

    followed by the next, lets say that worked for a second pathname:

    (size = 4, err = 0, value = "/tmp" )

    So we can skip the first while telling the user about the problem and
    then process the second.

    Cc: Adrian Hunter <adrian.hunter@intel.com>
    Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
    Cc: Jiri Olsa <jolsa@kernel.org>
    Cc: Luis Cláudio Gonçalves <lclaudio@redhat.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Link: https://lkml.kernel.org/n/tip-deyvqi39um6gp6hux6jovos8@git.kernel.org
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    ---
    .../examples/bpf/augmented_raw_syscalls.c | 46 +++++++++++++------
    1 file changed, 33 insertions(+), 13 deletions(-)

    diff --git a/tools/perf/examples/bpf/augmented_raw_syscalls.c b/tools/perf/examples/bpf/augmented_raw_syscalls.c
    index 356513e81ec1..5054b4bc9e55 100644
    --- a/tools/perf/examples/bpf/augmented_raw_syscalls.c
    +++ b/tools/perf/examples/bpf/augmented_raw_syscalls.c
    @@ -47,7 +47,7 @@ struct syscall_exit_args {

    struct augmented_filename {
    unsigned int size;
    - int reserved;
    + int err;
    char value[PATH_MAX];
    };

    @@ -61,16 +61,28 @@ struct augmented_args_filename {
    bpf_map(augmented_filename_map, PERCPU_ARRAY, int, struct augmented_args_filename, 1);

    static inline
    -unsigned int augmented_args__read_filename(struct augmented_args_filename *augmented_args,
    - const void *filename_arg, unsigned int filename_len)
    +unsigned int augmented_filename__read(struct augmented_filename *augmented_filename,
    + const void *filename_arg, unsigned int filename_len)
    {
    - unsigned int len = sizeof(*augmented_args);
    + unsigned int len = sizeof(*augmented_filename);
    + int size = probe_read_str(&augmented_filename->value, filename_len, filename_arg);

    - augmented_args->filename.reserved = 0;
    - augmented_args->filename.size = probe_read_str(&augmented_args->filename.value, filename_len, filename_arg);
    - if (augmented_args->filename.size < sizeof(augmented_args->filename.value)) {
    - len -= sizeof(augmented_args->filename.value) - augmented_args->filename.size;
    - len &= sizeof(augmented_args->filename.value) - 1;
    + augmented_filename->size = augmented_filename->err = 0;
    + /*
    + * probe_read_str may return < 0, e.g. -EFAULT
    + * So we leave that in the augmented_filename->size that userspace will
    + */
    + if (size > 0) {
    + len -= sizeof(augmented_filename->value) - size;
    + len &= sizeof(augmented_filename->value) - 1;
    + augmented_filename->size = size;
    + } else {
    + /*
    + * So that username notice the error while still being able
    + * to skip this augmented arg record
    + */
    + augmented_filename->err = size;
    + len = offsetof(struct augmented_filename, value);
    }

    return len;
    @@ -80,7 +92,17 @@ SEC("raw_syscalls:sys_enter")
    int sys_enter(struct syscall_enter_args *args)
    {
    struct augmented_args_filename *augmented_args;
    - unsigned int len, filename_len;
    + /*
    + * We start len, the amount of data that will be in the perf ring
    + * buffer, if this is not filtered out by one of pid_filter__has(),
    + * syscall->enabled, etc, with the non-augmented raw syscall payload,
    + * i.e. sizeof(augmented_args->args).
    + *
    + * We'll add to this as we add augmented syscalls right after that
    + * initial, non-augmented raw_syscalls:sys_enter payload.
    + */
    + unsigned int len = sizeof(augmented_args->args);
    + unsigned int filename_len;
    const void *filename_arg = NULL;
    struct syscall *syscall;
    int key = 0;
    @@ -198,9 +220,7 @@ processed 46 insns (limit 1000000) max_states_per_insn 0 total_states 12 peak_st
    loop_iter_last(5)

    if (filename_arg != NULL && filename_len <= sizeof(augmented_args->filename.value)) {
    - len = augmented_args__read_filename(augmented_args, filename_arg, filename_len);
    - } else {
    - len = sizeof(augmented_args->args);
    + len += augmented_filename__read(&augmented_args->filename, filename_arg, filename_len);
    }

    /* If perf_event_output fails, return non-zero so that it gets recorded unaugmented */
    --
    2.20.1
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