Commit a68fd6a6 authored by Howard Chu's avatar Howard Chu Committed by Arnaldo Carvalho de Melo
Browse files

perf trace: Collect augmented data using BPF 



Include trace_augment.h for TRACE_AUG_MAX_BUF, so that BPF reads
TRACE_AUG_MAX_BUF bytes of buffer maximum.

Determine what type of argument and how many bytes to read from user space, us ing the
value in the beauty_map. This is the relation of parameter type and its corres ponding
value in the beauty map, and how many bytes we read eventually:

string: 1                          -> size of string (till null)
struct: size of struct             -> size of struct
buffer: -1 * (index of paired len) -> value of paired len (maximum: TRACE_AUG_ MAX_BUF)

After reading from user space, we output the augmented data using
bpf_perf_event_output().

If the struct augmenter, augment_sys_enter() failed, we fall back to
using bpf_tail_call().

I have to make the payload 6 times the size of augmented_arg, to pass the
BPF verifier.

Signed-off-by: default avatarHoward Chu <howardchu95@gmail.com>
Tested-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240815013626.935097-10-howardchu95@gmail.com
Link: https://lore.kernel.org/r/20240824163322.60796-7-howardchu95@gmail.com


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent b257fac1

tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c

+106 −1
Original line number Diff line number Diff line
@@ -7,6 +7,8 @@ 
 */



#include "vmlinux.h"

#include "../trace_augment.h"



#include <bpf/bpf_helpers.h>

#include <linux/limits.h>
@@ -131,6 +133,18 @@ struct beauty_map_enter { 
	__uint(max_entries, 512);

} beauty_map_enter SEC(".maps");



struct beauty_payload_enter {

	struct syscall_enter_args args;

	struct augmented_arg aug_args[6];

};



struct beauty_payload_enter_map {

	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);

	__type(key, int);

	__type(value, struct beauty_payload_enter);

	__uint(max_entries, 1);

} beauty_payload_enter_map SEC(".maps");



static inline struct augmented_args_payload *augmented_args_payload(void)

{

	int key = 0;
@@ -143,6 +157,11 @@ static inline int augmented__output(void *ctx, struct augmented_args_payload *ar 
	return bpf_perf_event_output(ctx, &__augmented_syscalls__, BPF_F_CURRENT_CPU, args, len);

}



static inline int augmented__beauty_output(void *ctx, void *data, int len)

{

	return bpf_perf_event_output(ctx, &__augmented_syscalls__, BPF_F_CURRENT_CPU, data, len);

}



static inline

unsigned int augmented_arg__read_str(struct augmented_arg *augmented_arg, const void *arg, unsigned int arg_len)

{
@@ -401,6 +420,91 @@ static bool pid_filter__has(struct pids_filtered *pids, pid_t pid) 
	return bpf_map_lookup_elem(pids, &pid) != NULL;

}



static int augment_sys_enter(void *ctx, struct syscall_enter_args *args)

{

	bool augmented, do_output = false;

	int zero = 0, size, aug_size, index, output = 0,

	    value_size = sizeof(struct augmented_arg) - offsetof(struct augmented_arg, value);

	unsigned int nr, *beauty_map;

	struct beauty_payload_enter *payload;

	void *arg, *payload_offset;



	/* fall back to do predefined tail call */

	if (args == NULL)

		return 1;



	/* use syscall number to get beauty_map entry */

	nr             = (__u32)args->syscall_nr;

	beauty_map     = bpf_map_lookup_elem(&beauty_map_enter, &nr);



	/* set up payload for output */

	payload        = bpf_map_lookup_elem(&beauty_payload_enter_map, &zero);

	payload_offset = (void *)&payload->aug_args;



	if (beauty_map == NULL || payload == NULL)

		return 1;



	/* copy the sys_enter header, which has the syscall_nr */

	__builtin_memcpy(&payload->args, args, sizeof(struct syscall_enter_args));



	/*

	 * Determine what type of argument and how many bytes to read from user space, using the

	 * value in the beauty_map. This is the relation of parameter type and its corresponding

	 * value in the beauty map, and how many bytes we read eventually:

	 *

	 * string: 1			      -> size of string

	 * struct: size of struct	      -> size of struct

	 * buffer: -1 * (index of paired len) -> value of paired len (maximum: TRACE_AUG_MAX_BUF)

	 */

	for (int i = 0; i < 6; i++) {

		arg = (void *)args->args[i];

		augmented = false;

		size = beauty_map[i];

		aug_size = size; /* size of the augmented data read from user space */



		if (size == 0 || arg == NULL)

			continue;



		if (size == 1) { /* string */

			aug_size = bpf_probe_read_user_str(((struct augmented_arg *)payload_offset)->value, value_size, arg);

			/* minimum of 0 to pass the verifier */

			if (aug_size < 0)

				aug_size = 0;



			augmented = true;

		} else if (size > 0 && size <= value_size) { /* struct */

			if (!bpf_probe_read_user(((struct augmented_arg *)payload_offset)->value, size, arg))

				augmented = true;

		} else if (size < 0 && size >= -6) { /* buffer */

			index = -(size + 1);

			aug_size = args->args[index];



			if (aug_size > TRACE_AUG_MAX_BUF)

				aug_size = TRACE_AUG_MAX_BUF;



			if (aug_size > 0) {

				if (!bpf_probe_read_user(((struct augmented_arg *)payload_offset)->value, aug_size, arg))

					augmented = true;

			}

		}



		/* write data to payload */

		if (augmented) {

			int written = offsetof(struct augmented_arg, value) + aug_size;



			((struct augmented_arg *)payload_offset)->size = aug_size;

			output += written;

			payload_offset += written;

			do_output = true;

		}

	}



	if (!do_output)

		return 1;



	return augmented__beauty_output(ctx, payload, sizeof(struct syscall_enter_args) + output);

}



SEC("tp/raw_syscalls/sys_enter")

int sys_enter(struct syscall_enter_args *args)

{
@@ -429,6 +533,7 @@ int sys_enter(struct syscall_enter_args *args) 
	 * "!raw_syscalls:unaugmented" that will just return 1 to return the

	 * unaugmented tracepoint payload.

	 */

	if (augment_sys_enter(args, &augmented_args->args))

		bpf_tail_call(args, &syscalls_sys_enter, augmented_args->args.syscall_nr);



	// If not found on the PROG_ARRAY syscalls map, then we're filtering it: