linux/tools/perf/examples/bpf/augmented_raw_syscalls.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Augment the raw_syscalls tracepoints with the contents of the pointer arguments.
 *
 * Test it with:
 *
 * perf trace -e tools/perf/examples/bpf/augmented_raw_syscalls.c cat /etc/passwd > /dev/null
 *
 * This exactly matches what is marshalled into the raw_syscall:sys_enter
 * payload expected by the 'perf trace' beautifiers.
 *
 * For now it just uses the existing tracepoint augmentation code in 'perf
 * trace', in the next csets we'll hook up these with the sys_enter/sys_exit
 * code that will combine entry/exit in a strace like way.
 */

#include <unistd.h>
#include <linux/limits.h>
#include <pid_filter.h>

/* bpf-output associated map */
bpf_map(__augmented_syscalls__, PERF_EVENT_ARRAY, int, u32, __NR_CPUS__);

/*
 * string_args_len: one per syscall arg, 0 means not a string or don't copy it,
 * 		    PATH_MAX for copying everything, any other value to limit
 * 		    it a la 'strace -s strsize'.
 */
struct syscall {
	bool	enabled;
	u16	string_args_len[6];
};

bpf_map(syscalls, ARRAY, int, struct syscall, 512);

/*
 * What to augment at entry?
 *
 * Pointer arg payloads (filenames, etc) passed from userspace to the kernel
 */
bpf_map(syscalls_sys_enter, PROG_ARRAY, u32, u32, 512);

/*
 * What to augment at exit?
 *
 * Pointer arg payloads returned from the kernel (struct stat, etc) to userspace.
 */
bpf_map(syscalls_sys_exit, PROG_ARRAY, u32, u32, 512);

struct syscall_enter_args {
	unsigned long long common_tp_fields;
	long		   syscall_nr;
	unsigned long	   args[6];
};

struct syscall_exit_args {
	unsigned long long common_tp_fields;
	long		   syscall_nr;
	long		   ret;
};

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

pid_filter(pids_filtered);

struct augmented_args_filename {
       struct syscall_enter_args args;
       struct augmented_filename filename;
};

bpf_map(augmented_filename_map, PERCPU_ARRAY, int, struct augmented_args_filename, 1);

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

	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;
}

SEC("!raw_syscalls:unaugmented")
int syscall_unaugmented(struct syscall_enter_args *args)
{
	return 1;
}

/*
 * This will be tail_called from SEC("raw_syscalls:sys_enter"), so will find in
 * augmented_filename_map what was read by that raw_syscalls:sys_enter and go
 * on from there, reading the first syscall arg as a string, i.e. open's
 * filename.
 */
SEC("!syscalls:sys_enter_open")
int sys_enter_open(struct syscall_enter_args *args)
{
	int key = 0;
	struct augmented_args_filename *augmented_args = bpf_map_lookup_elem(&augmented_filename_map, &key);
	const void *filename_arg = (const void *)args->args[0];
	unsigned int len = sizeof(augmented_args->args);

        if (augmented_args == NULL)
                return 1; /* Failure: don't filter */

	len += augmented_filename__read(&augmented_args->filename, filename_arg, sizeof(augmented_args->filename.value));

	/* If perf_event_output fails, return non-zero so that it gets recorded unaugmented */
	return perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU, augmented_args, len);
}

SEC("!syscalls:sys_enter_openat")
int sys_enter_openat(struct syscall_enter_args *args)
{
	int key = 0;
	struct augmented_args_filename *augmented_args = bpf_map_lookup_elem(&augmented_filename_map, &key);
	const void *filename_arg = (const void *)args->args[1];
	unsigned int len = sizeof(augmented_args->args);

        if (augmented_args == NULL)
                return 1; /* Failure: don't filter */

	len += augmented_filename__read(&augmented_args->filename, filename_arg, sizeof(augmented_args->filename.value));

	/* If perf_event_output fails, return non-zero so that it gets recorded unaugmented */
	return perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU, augmented_args, len);
}

SEC("raw_syscalls:sys_enter")
int sys_enter(struct syscall_enter_args *args)
{
	struct augmented_args_filename *augmented_args;
	/*
	 * 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);
	struct syscall *syscall;
	int key = 0;

        augmented_args = bpf_map_lookup_elem(&augmented_filename_map, &key);
        if (augmented_args == NULL)
                return 1;

	if (pid_filter__has(&pids_filtered, getpid()))
		return 0;

	probe_read(&augmented_args->args, sizeof(augmented_args->args), args);

	/*
	 * Jump to syscall specific augmenter, even if the default one,
	 * "!raw_syscalls:unaugmented" that will just return 1 to return the
	 * unagmented tracepoint payload.
	 */
	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:
	return 0;
}

SEC("raw_syscalls:sys_exit")
int sys_exit(struct syscall_exit_args *args)
{
	struct syscall_exit_args exit_args;

	if (pid_filter__has(&pids_filtered, getpid()))
		return 0;

	probe_read(&exit_args, sizeof(exit_args), args);
	/*
	 * Jump to syscall specific return augmenter, even if the default one,
	 * "!raw_syscalls:unaugmented" that will just return 1 to return the
	 * unagmented tracepoint payload.
	 */
	bpf_tail_call(args, &syscalls_sys_exit, exit_args.syscall_nr);
	/*
	 * If not found on the PROG_ARRAY syscalls map, then we're filtering it:
	 */
	return 0;
}

license(GPL);