lkml.org 
[lkml]   [2019]   [Sep]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [RFC v1 13/14] krsi: Provide an example to read and log environment variables
Date


On 9/10/19 12:55 PM, KP Singh wrote:
> From: KP Singh <kpsingh@google.com>
>
> * The program takes the name of an environment variable as an
> argument.
> * An eBPF program is loaded and attached to the
> process_execution hook.
> * The name of the environment variable passed is updated in a
> eBPF per-cpu map.
> * The eBPF program uses the krsi_get_env_var helper to get the
> the value of this variable and logs the result to the perf
> events buffer.
> * The user-space program listens to the perf events and prints
> the values.
>
> Example execution:
>
> ./krsi LD_PRELOAD
>
> [p_pid=123] LD_PRELOAD is not set
> [p_pid=456] LD_PRELOAD=/lib/bad.so
> [p_pid=789] WARNING! LD_PRELOAD is set 2 times
> [p_pid=789] LD_PRELOAD=/lib/decoy.so
> [p_pid=789] LD_PRELOAD=/lib/bad.so
>
> In a separate session the following [1, 2, 3] exec system calls
> are made where:
>
> [1, 2, 3] char *argv[] = {"/bin/ls", 0};
>
> [1] char *envp = {0};
> [2] char *envp = {"LD_PRELOAD=/lib/bad.so", 0};
> [3] char *envp = {"LD_PRELOAD=/lib/decoy.so, "LD_PRELOAD=/lib/bad.so", 0};
>
> This example demonstrates that user-space is free to choose the format
> in which the data is logged and can use very specific helpers like
> krsi_get_env_var to populate only the data that is required.
>
> Signed-off-by: KP Singh <kpsingh@google.com>
> ---
> MAINTAINERS | 3 +
> samples/bpf/.gitignore | 1 +
> samples/bpf/Makefile | 3 +
> samples/bpf/krsi_helpers.h | 31 ++++++
> samples/bpf/krsi_kern.c | 52 ++++++++++
> samples/bpf/krsi_user.c | 202 +++++++++++++++++++++++++++++++++++++

The KRSI does not depend on kernel headers.
I would recommend to put this into tools/testing/selftests/bpf
as a selftest. Selftest is the place to test regressions with
bpf changes.

The krsi_kern.c can be put into tools/testing/selftests/bpf/progs
and krsi_user.c can be put into tools/testing/selftests/bpf/prog_tests.

> 6 files changed, 292 insertions(+)
> create mode 100644 samples/bpf/krsi_helpers.h
> create mode 100644 samples/bpf/krsi_kern.c
> create mode 100644 samples/bpf/krsi_user.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 8e0364391d8b..ec378abb4c23 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9005,6 +9005,9 @@ F: kernel/kprobes.c
> KRSI SECURITY MODULE
> M: KP Singh <kpsingh@chromium.org>
> S: Supported
> +F: samples/bpf/krsi_helpers.h
> +F: samples/bpf/krsi_kern.c
> +F: samples/bpf/krsi_user.c
> F: security/krsi/
>
> KS0108 LCD CONTROLLER DRIVER
> diff --git a/samples/bpf/.gitignore b/samples/bpf/.gitignore
> index 74d31fd3c99c..6bbf5a04877f 100644
> --- a/samples/bpf/.gitignore
> +++ b/samples/bpf/.gitignore
> @@ -2,6 +2,7 @@ cpustat
> fds_example
> hbm
> ibumad
> +krsi
> lathist
> lwt_len_hist
> map_perf_test
> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> index 1d9be26b4edd..33d3bef17549 100644
> --- a/samples/bpf/Makefile
> +++ b/samples/bpf/Makefile
> @@ -8,6 +8,7 @@ hostprogs-y := test_lru_dist
> hostprogs-y += sock_example
> hostprogs-y += fds_example
> hostprogs-y += sockex1
> +hostprogs-y += krsi
> hostprogs-y += sockex2
> hostprogs-y += sockex3
> hostprogs-y += tracex1
> @@ -62,6 +63,7 @@ TRACE_HELPERS := ../../tools/testing/selftests/bpf/trace_helpers.o
>
> fds_example-objs := fds_example.o
> sockex1-objs := sockex1_user.o
> +krsi-objs := krsi_user.o $(TRACE_HELPERS)
> sockex2-objs := sockex2_user.o
> sockex3-objs := bpf_load.o sockex3_user.o
> tracex1-objs := bpf_load.o tracex1_user.o
> @@ -113,6 +115,7 @@ hbm-objs := bpf_load.o hbm.o $(CGROUP_HELPERS)
> # Tell kbuild to always build the programs
> always := $(hostprogs-y)
> always += sockex1_kern.o
> +always += krsi_kern.o
> always += sockex2_kern.o
> always += sockex3_kern.o
> always += tracex1_kern.o
> diff --git a/samples/bpf/krsi_helpers.h b/samples/bpf/krsi_helpers.h
> new file mode 100644
> index 000000000000..3007bfd6212e
> --- /dev/null
> +++ b/samples/bpf/krsi_helpers.h
> @@ -0,0 +1,31 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _KRSI_HELPERS_H
> +#define _KRSI_HELPERS_H
> +
> +#define __bpf_percpu_val_align __aligned(8)
> +
> +#define ENV_VAR_NAME_MAX_LEN 48
> +#define ENV_VAR_VAL_MAX_LEN 4096
> +
> +#define MAX_CPUS 128
> +
> +#define __LOWER(x) (x & 0xffffffff)
> +#define __UPPER(x) (x >> 32)
> +
> +struct krsi_env_value {
> + // The name of the environment variable.
> + char name[ENV_VAR_NAME_MAX_LEN];
> + // The value of the environment variable (if set).
> + char value[ENV_VAR_VAL_MAX_LEN];
> + // Indicates if an overflow occurred while reading the value of the
> + // of the environment variable. This means that an -E2BIG was received
> + // from the krsi_get_env_var helper.
> + bool overflow;
> + // The number of times the environment variable was set.
> + __u32 times;
> + // The PID of the parent process.
> + __u32 p_pid;
> +} __bpf_percpu_val_align;
> +
> +#endif // _KRSI_HELPERS_H
> diff --git a/samples/bpf/krsi_kern.c b/samples/bpf/krsi_kern.c
> new file mode 100644
> index 000000000000..087a6f0cc81d
> --- /dev/null
> +++ b/samples/bpf/krsi_kern.c
> @@ -0,0 +1,52 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/ptrace.h>
> +#include <uapi/linux/bpf.h>
> +#include <uapi/linux/ip.h>
> +#include "bpf_helpers.h"
> +#include "krsi_helpers.h"
> +
> +#define MAX_CPUS 128
> +
> +struct bpf_map_def SEC("maps") env_map = {
> + .type = BPF_MAP_TYPE_PERCPU_ARRAY,
> + .key_size = sizeof(u32),
> + .value_size = sizeof(struct krsi_env_value),
> + .max_entries = 1,
> +};
> +
> +struct bpf_map_def SEC("maps") perf_map = {
> + .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> + .key_size = sizeof(int),
> + .value_size = sizeof(u32),
> + .max_entries = MAX_CPUS,
> +};
> +
> +SEC("krsi")
> +int env_dumper(void *ctx)
> +{
> + u64 times_ret;
> + s32 ret;
> + u32 map_id = 0;
> + char *map_value;
> + struct krsi_env_value *env;
> +
> + env = bpf_map_lookup_elem(&env_map, &map_id);
> + if (!env)
> + return -ENOMEM;
> + times_ret = krsi_get_env_var(ctx, env->name, ENV_VAR_NAME_MAX_LEN,
> + env->value, ENV_VAR_VAL_MAX_LEN);
> + ret = __LOWER(times_ret);
> + if (ret == -E2BIG)
> + env->overflow = true;
> + else if (ret < 0)
> + return ret;
> +
> + env->times = __UPPER(times_ret);
> + env->p_pid = bpf_get_current_pid_tgid();
> + bpf_perf_event_output(ctx, &perf_map, BPF_F_CURRENT_CPU, env,
> + sizeof(struct krsi_env_value));
> +
> + return 0;
> +}
> +char _license[] SEC("license") = "GPL";
> diff --git a/samples/bpf/krsi_user.c b/samples/bpf/krsi_user.c
> new file mode 100644
> index 000000000000..1fad29bf017a
> --- /dev/null
> +++ b/samples/bpf/krsi_user.c
> @@ -0,0 +1,202 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <errno.h>
> +#include <err.h>
> +#include <assert.h>
> +#include <linux/limits.h>
> +#include <linux/bpf.h>
> +#include <bpf/bpf.h>
> +#include "bpf/libbpf.h"
> +#include <unistd.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <sys/sysinfo.h>
> +#include <sys/ioctl.h>
> +#include <fcntl.h>
> +#include <sys/resource.h>
> +
> +#include "perf-sys.h"
> +#include "trace_helpers.h"
> +#include "krsi_helpers.h"
> +
> +#define LSM_HOOK_PATH "/sys/kernel/security/krsi/process_execution"
> +
> +static int pmu_fds[MAX_CPUS];
> +static struct perf_event_mmap_page *headers[MAX_CPUS];
> +
> +static int print_env(void *d, int size)
> +{
> + struct krsi_env_value *env = d;
> + int times = env->times;
> + char *next = env->value;
> + size_t total = 0;
> +
> + if (env->times > 1)
> + printf("[p_pid=%u] WARNING! %s is set %u times\n",
> + env->p_pid, env->name, env->times);
> +
> + /*
> + * krsi_get_env_var ensures that even overflows
> + * are null terminated. Incase of an overflow,
> + * this logic tries to print as much information
> + * that was gathered.
> + */
> + while (times && total < ENV_VAR_NAME_MAX_LEN) {
> + next += total;
> + if (env->overflow)
> + printf("[p_pid=%u] OVERFLOW! %s=%s\n",
> + env->p_pid, env->name, next);
> + else
> + printf("[p_pid=%u] %s=%s\n",
> + env->p_pid, env->name, next);
> + times--;
> + total += strlen(next) + 1;
> + }
> +
> + if (!env->times)
> + printf("p_pid=%u] %s is not set\n",
> + env->p_pid, env->name);
> +
> + return LIBBPF_PERF_EVENT_CONT;
> +}
> +
> +static int open_perf_events(int map_fd, int num)
> +{
> + int i;
> + struct perf_event_attr attr = {
> + .sample_type = PERF_SAMPLE_RAW,
> + .type = PERF_TYPE_SOFTWARE,
> + .config = PERF_COUNT_SW_BPF_OUTPUT,
> + .wakeup_events = 1, /* get an fd notification for every event */
> + };
> +
> + for (i = 0; i < num; i++) {
> + int key = i;
> + int ret;
> +
> + ret = sys_perf_event_open(&attr, -1 /*pid*/, i/*cpu*/,
> + -1/*group_fd*/, 0);
> + if (ret < 0)
> + return ret;
> + pmu_fds[i] = ret;
> + ret = bpf_map_update_elem(map_fd, &key, &pmu_fds[i], BPF_ANY);
> + if (ret < 0)
> + return ret;
> + ioctl(pmu_fds[i], PERF_EVENT_IOC_ENABLE, 0);
> + }
> + return 0;
> +}
> +
> +static int update_env_map(struct bpf_object *prog_obj, const char *env_var_name,
> + int numcpus)
> +{
> + struct bpf_map *map;
> + struct krsi_env_value *env;
> + int map_fd;
> + int key = 0, ret = 0, i;
> +
> + map = bpf_object__find_map_by_name(prog_obj, "env_map");
> + if (!map)
> + return -EINVAL;
> +
> + map_fd = bpf_map__fd(map);
> + if (map_fd < 0)
> + return map_fd;
> +
> + env = malloc(numcpus * sizeof(struct krsi_env_value));
> + if (!env) {
> + ret = -ENOMEM;
> + goto out;
> + }
> +
> + for (i = 0; i < numcpus; i++)
> + strcpy(env[i].name, env_var_name);
> +
> + ret = bpf_map_update_elem(map_fd, &key, env, BPF_ANY);
> + if (ret < 0)
> + goto out;
> +
> +out:
> + free(env);
> + return ret;
> +}
> +
> +int main(int argc, char **argv)
> +{
> + struct bpf_object *prog_obj;
> + const char *env_var_name;
> + struct bpf_prog_load_attr attr;
> + int prog_fd, target_fd, map_fd;
> + int ret, i, numcpus;
> + struct bpf_map *map;
> + char filename[PATH_MAX];
> + struct rlimit r = {RLIM_INFINITY, RLIM_INFINITY};
> +
> +
> + if (argc != 2)
> + errx(EXIT_FAILURE, "Usage %s env_var_name\n", argv[0]);
> +
> + env_var_name = argv[1];
> + if (strlen(env_var_name) > ENV_VAR_NAME_MAX_LEN - 1)
> + errx(EXIT_FAILURE,
> + "<env_var_name> cannot be more than %d in length",
> + ENV_VAR_NAME_MAX_LEN - 1);
> +
> +
> + setrlimit(RLIMIT_MEMLOCK, &r);
> + snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
> +
> + memset(&attr, 0, sizeof(struct bpf_prog_load_attr));
> + attr.prog_type = BPF_PROG_TYPE_KRSI;
> + attr.expected_attach_type = BPF_KRSI;
> + attr.file = filename;
> +
> + /* Attach the BPF program to the given hook */
> + target_fd = open(LSM_HOOK_PATH, O_RDWR);
> + if (target_fd < 0)
> + err(EXIT_FAILURE, "Failed to open target file");
> +
> + if (bpf_prog_load_xattr(&attr, &prog_obj, &prog_fd))
> + err(EXIT_FAILURE, "Failed to load eBPF program");
> +
> + numcpus = get_nprocs();
> + if (numcpus > MAX_CPUS)
> + numcpus = MAX_CPUS;
> +
> + ret = update_env_map(prog_obj, env_var_name, numcpus);
> + if (ret < 0)
> + err(EXIT_FAILURE, "Failed to update env map");
> +
> + map = bpf_object__find_map_by_name(prog_obj, "perf_map");
> + if (!map)
> + err(EXIT_FAILURE,
> + "Finding the perf event map in obj file failed");
> +
> + map_fd = bpf_map__fd(map);
> + if (map_fd < 0)
> + err(EXIT_FAILURE, "Failed to get fd for perf events map");
> +
> + ret = bpf_prog_attach(prog_fd, target_fd, BPF_KRSI,
> + BPF_F_ALLOW_OVERRIDE);
> + if (ret < 0)
> + err(EXIT_FAILURE, "Failed to attach prog to LSM hook");
> +
> + ret = open_perf_events(map_fd, numcpus);
> + if (ret < 0)
> + err(EXIT_FAILURE, "Failed to open perf events handler");
> +
> + for (i = 0; i < numcpus; i++) {
> + ret = perf_event_mmap_header(pmu_fds[i], &headers[i]);
> + if (ret < 0)
> + err(EXIT_FAILURE, "perf_event_mmap_header");
> + }
> +
> + ret = perf_event_poller_multi(pmu_fds, headers, numcpus, print_env);
> + if (ret < 0)
> + err(EXIT_FAILURE, "Failed to poll perf events");
> +
> + return EXIT_SUCCESS;
> +}
>
\
 
 \ /
  Last update: 2019-09-15 02:27    [W:0.470 / U:0.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site