Re: [RFC v1 13/14] krsi: Provide an example to read and log environment variables

[Yonghong Song <yhs@fb.com>]

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;
> +}
>