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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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