selftests/bpf: Add tests for libbpf-provided externs

Add a set of tests validating libbpf-provided extern variables. One crucial
feature that's tested is dead code elimination together with using invalid BPF
helper. CONFIG_MISSING is not supposed to exist and should always be specified
by libbpf as zero, which allows BPF verifier to correctly do branch pruning
and not fail validation, when invalid BPF helper is called from dead if branch.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191214014710.3449601-5-andriin@fb.com

tools/testing/selftests/bpf/prog_tests/core_extern.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2019 Facebook */
+
+#include <test_progs.h>
+#include <sys/mman.h>
+#include <sys/utsname.h>
+#include <linux/version.h>
+#include "test_core_extern.skel.h"
+
+static uint32_t get_kernel_version(void)
+{
+	uint32_t major, minor, patch;
+	struct utsname info;
+
+	uname(&info);
+	if (sscanf(info.release, "%u.%u.%u", &major, &minor, &patch) != 3)
+		return 0;
+	return KERNEL_VERSION(major, minor, patch);
+}
+
+#define CFG "CONFIG_BPF_SYSCALL=n\n"
+
+static struct test_case {
+	const char *name;
+	const char *cfg;
+	const char *cfg_path;
+	bool fails;
+	struct test_core_extern__data data;
+} test_cases[] = {
+	{ .name = "default search path", .cfg_path = NULL,
+	  .data = { .bpf_syscall = true } },
+	{ .name = "/proc/config.gz", .cfg_path = "/proc/config.gz",
+	  .data = { .bpf_syscall = true } },
+	{ .name = "missing config", .fails = true,
+	  .cfg_path = "/proc/invalid-config.gz" },
+	{
+		.name = "custom values",
+		.cfg = "CONFIG_BPF_SYSCALL=y\n"
+		       "CONFIG_TRISTATE=m\n"
+		       "CONFIG_BOOL=y\n"
+		       "CONFIG_CHAR=100\n"
+		       "CONFIG_USHORT=30000\n"
+		       "CONFIG_INT=123456\n"
+		       "CONFIG_ULONG=0xDEADBEEFC0DE\n"
+		       "CONFIG_STR=\"abracad\"\n"
+		       "CONFIG_MISSING=0",
+		.data = {
+			.bpf_syscall = true,
+			.tristate_val = TRI_MODULE,
+			.bool_val = true,
+			.char_val = 100,
+			.ushort_val = 30000,
+			.int_val = 123456,
+			.ulong_val = 0xDEADBEEFC0DE,
+			.str_val = "abracad",
+		},
+	},
+	/* TRISTATE */
+	{ .name = "tristate (y)", .cfg = CFG"CONFIG_TRISTATE=y\n",
+	  .data = { .tristate_val = TRI_YES } },
+	{ .name = "tristate (n)", .cfg = CFG"CONFIG_TRISTATE=n\n",
+	  .data = { .tristate_val = TRI_NO } },
+	{ .name = "tristate (m)", .cfg = CFG"CONFIG_TRISTATE=m\n",
+	  .data = { .tristate_val = TRI_MODULE } },
+	{ .name = "tristate (int)", .fails = 1, .cfg = CFG"CONFIG_TRISTATE=1" },
+	{ .name = "tristate (bad)", .fails = 1, .cfg = CFG"CONFIG_TRISTATE=M" },
+	/* BOOL */
+	{ .name = "bool (y)", .cfg = CFG"CONFIG_BOOL=y\n",
+	  .data = { .bool_val = true } },
+	{ .name = "bool (n)", .cfg = CFG"CONFIG_BOOL=n\n",
+	  .data = { .bool_val = false } },
+	{ .name = "bool (tristate)", .fails = 1, .cfg = CFG"CONFIG_BOOL=m" },
+	{ .name = "bool (int)", .fails = 1, .cfg = CFG"CONFIG_BOOL=1" },
+	/* CHAR */
+	{ .name = "char (tristate)", .cfg = CFG"CONFIG_CHAR=m\n",
+	  .data = { .char_val = 'm' } },
+	{ .name = "char (bad)", .fails = 1, .cfg = CFG"CONFIG_CHAR=q\n" },
+	{ .name = "char (empty)", .fails = 1, .cfg = CFG"CONFIG_CHAR=\n" },
+	{ .name = "char (str)", .fails = 1, .cfg = CFG"CONFIG_CHAR=\"y\"\n" },
+	/* STRING */
+	{ .name = "str (empty)", .cfg = CFG"CONFIG_STR=\"\"\n",
+	  .data = { .str_val = "\0\0\0\0\0\0\0" } },
+	{ .name = "str (padded)", .cfg = CFG"CONFIG_STR=\"abra\"\n",
+	  .data = { .str_val = "abra\0\0\0" } },
+	{ .name = "str (too long)", .cfg = CFG"CONFIG_STR=\"abracada\"\n",
+	  .data = { .str_val = "abracad" } },
+	{ .name = "str (no value)", .fails = 1, .cfg = CFG"CONFIG_STR=\n" },
+	{ .name = "str (bad value)", .fails = 1, .cfg = CFG"CONFIG_STR=bla\n" },
+	/* INTEGERS */
+	{
+		.name = "integer forms",
+		.cfg = CFG
+		       "CONFIG_CHAR=0xA\n"
+		       "CONFIG_USHORT=0462\n"
+		       "CONFIG_INT=-100\n"
+		       "CONFIG_ULONG=+1000000000000",
+		.data = {
+			.char_val = 0xA,
+			.ushort_val = 0462,
+			.int_val = -100,
+			.ulong_val = 1000000000000,
+		},
+	},
+	{ .name = "int (bad)", .fails = 1, .cfg = CFG"CONFIG_INT=abc" },
+	{ .name = "int (str)", .fails = 1, .cfg = CFG"CONFIG_INT=\"abc\"" },
+	{ .name = "int (empty)", .fails = 1, .cfg = CFG"CONFIG_INT=" },
+	{ .name = "int (mixed)", .fails = 1, .cfg = CFG"CONFIG_INT=123abc" },
+	{ .name = "int (max)", .cfg = CFG"CONFIG_INT=2147483647",
+	  .data = { .int_val = 2147483647 } },
+	{ .name = "int (min)", .cfg = CFG"CONFIG_INT=-2147483648",
+	  .data = { .int_val = -2147483648 } },
+	{ .name = "int (max+1)", .fails = 1, .cfg = CFG"CONFIG_INT=2147483648" },
+	{ .name = "int (min-1)", .fails = 1, .cfg = CFG"CONFIG_INT=-2147483649" },
+	{ .name = "ushort (max)", .cfg = CFG"CONFIG_USHORT=65535",
+	  .data = { .ushort_val = 65535 } },
+	{ .name = "ushort (min)", .cfg = CFG"CONFIG_USHORT=0",
+	  .data = { .ushort_val = 0 } },
+	{ .name = "ushort (max+1)", .fails = 1, .cfg = CFG"CONFIG_USHORT=65536" },
+	{ .name = "ushort (min-1)", .fails = 1, .cfg = CFG"CONFIG_USHORT=-1" },
+	{ .name = "u64 (max)", .cfg = CFG"CONFIG_ULONG=0xffffffffffffffff",
+	  .data = { .ulong_val = 0xffffffffffffffff } },
+	{ .name = "u64 (min)", .cfg = CFG"CONFIG_ULONG=0",
+	  .data = { .ulong_val = 0 } },
+	{ .name = "u64 (max+1)", .fails = 1, .cfg = CFG"CONFIG_ULONG=0x10000000000000000" },
+};
+
+BPF_EMBED_OBJ(core_extern, "test_core_extern.o");
+
+void test_core_extern(void)
+{
+	const uint32_t kern_ver = get_kernel_version();
+	int err, duration = 0, i, j;
+	struct test_core_extern *skel = NULL;
+	uint64_t *got, *exp;
+	int n = sizeof(*skel->data) / sizeof(uint64_t);
+
+	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
+		char tmp_cfg_path[] = "/tmp/test_core_extern_cfg.XXXXXX";
+		struct test_case *t = &test_cases[i];
+		DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
+			.kconfig_path = t->cfg_path,
+		);
+
+		if (!test__start_subtest(t->name))
+			continue;
+
+		if (t->cfg) {
+			size_t n = strlen(t->cfg) + 1;
+			int fd = mkstemp(tmp_cfg_path);
+			int written;
+
+			if (CHECK(fd < 0, "mkstemp", "errno: %d\n", errno))
+				continue;
+			printf("using '%s' as config file\n", tmp_cfg_path);
+			written = write(fd, t->cfg, n);
+			close(fd);
+			if (CHECK_FAIL(written != n))
+				goto cleanup;
+			opts.kconfig_path = tmp_cfg_path;
+		}
+
+		skel = test_core_extern__open_opts(&core_extern_embed, &opts);
+		if (CHECK(!skel, "skel_open", "skeleton open failed\n"))
+			goto cleanup;
+		err = test_core_extern__load(skel);
+		if (t->fails) {
+			CHECK(!err, "skel_load",
+			      "shouldn't succeed open/load of skeleton\n");
+			goto cleanup;
+		} else if (CHECK(err, "skel_load",
+				 "failed to open/load skeleton\n")) {
+			goto cleanup;
+		}
+		err = test_core_extern__attach(skel);
+		if (CHECK(err, "attach_raw_tp", "failed attach: %d\n", err))
+			goto cleanup;
+
+		usleep(1);
+
+		t->data.kern_ver = kern_ver;
+		t->data.missing_val = 0xDEADC0DE;
+		got = (uint64_t *)skel->data;
+		exp = (uint64_t *)&t->data;
+		for (j = 0; j < n; j++) {
+			CHECK(got[j] != exp[j], "check_res",
+			      "result #%d: expected %lx, but got %lx\n",
+			       j, exp[j], got[j]);
+		}
+cleanup:
+		if (t->cfg)
+			unlink(tmp_cfg_path);
+		test_core_extern__destroy(skel);
+		skel = NULL;
+	}
+}

tools/testing/selftests/bpf/prog_tests/skeleton.c

@@ -17,11 +17,21 @@ void test_skeleton(void)
 	int duration = 0, err;
 	struct test_skeleton* skel;
 	struct test_skeleton__bss *bss;
+	struct test_skeleton__externs *exts;
 
-	skel = test_skeleton__open_and_load(&skeleton_embed);
+	skel = test_skeleton__open(&skeleton_embed);
 	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
 		return;
 
+	printf("EXTERNS BEFORE: %p\n", skel->externs);
+	if (CHECK(skel->externs, "skel_externs", "externs are mmaped()!\n"))
+		goto cleanup;
+
+	err = test_skeleton__load(skel);
+	if (CHECK(err, "skel_load", "failed to load skeleton: %d\n", err))
+		goto cleanup;
+	printf("EXTERNS AFTER: %p\n", skel->externs);
+
 	bss = skel->bss;
 	bss->in1 = 1;
 	bss->in2 = 2;
@@ -29,6 +39,7 @@ void test_skeleton(void)
 	bss->in4 = 4;
 	bss->in5.a = 5;
 	bss->in5.b = 6;
+	exts = skel->externs;
 
 	err = test_skeleton__attach(skel);
 	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
@@ -46,6 +57,11 @@ void test_skeleton(void)
 	CHECK(bss->handler_out5.b != 6, "res6", "got %lld != exp %d\n",
 	      bss->handler_out5.b, 6);
 
+	CHECK(bss->bpf_syscall != exts->CONFIG_BPF_SYSCALL, "ext1",
+	      "got %d != exp %d\n", bss->bpf_syscall, exts->CONFIG_BPF_SYSCALL);
+	CHECK(bss->kern_ver != exts->LINUX_KERNEL_VERSION, "ext2",
+	      "got %d != exp %d\n", bss->kern_ver, exts->LINUX_KERNEL_VERSION);
+
 cleanup:
 	test_skeleton__destroy(skel);
 }

tools/testing/selftests/bpf/progs/test_core_extern.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2019 Facebook */
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <linux/ptrace.h>
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+/* non-existing BPF helper, to test dead code elimination */
+static int (*bpf_missing_helper)(const void *arg1, int arg2) = (void *) 999;
+
+extern int LINUX_KERNEL_VERSION;
+extern bool CONFIG_BPF_SYSCALL; /* strong */
+extern enum libbpf_tristate CONFIG_TRISTATE __weak;
+extern bool CONFIG_BOOL __weak;
+extern char CONFIG_CHAR __weak;
+extern uint16_t CONFIG_USHORT __weak;
+extern int CONFIG_INT __weak;
+extern uint64_t CONFIG_ULONG __weak;
+extern const char CONFIG_STR[8] __weak;
+extern uint64_t CONFIG_MISSING __weak;
+
+uint64_t kern_ver = -1;
+uint64_t bpf_syscall = -1;
+uint64_t tristate_val = -1;
+uint64_t bool_val = -1;
+uint64_t char_val = -1;
+uint64_t ushort_val = -1;
+uint64_t int_val = -1;
+uint64_t ulong_val = -1;
+char str_val[8] = {-1, -1, -1, -1, -1, -1, -1, -1};
+uint64_t missing_val = -1;
+
+SEC("raw_tp/sys_enter")
+int handle_sys_enter(struct pt_regs *ctx)
+{
+	int i;
+
+	kern_ver = LINUX_KERNEL_VERSION;
+	bpf_syscall = CONFIG_BPF_SYSCALL;
+	tristate_val = CONFIG_TRISTATE;
+	bool_val = CONFIG_BOOL;
+	char_val = CONFIG_CHAR;
+	ushort_val = CONFIG_USHORT;
+	int_val = CONFIG_INT;
+	ulong_val = CONFIG_ULONG;
+
+	for (i = 0; i < sizeof(CONFIG_STR); i++) {
+		str_val[i] = CONFIG_STR[i];
+	}
+
+	if (CONFIG_MISSING)
+		/* invalid, but dead code - never executed */
+		missing_val = bpf_missing_helper(ctx, 123);
+	else
+		missing_val = 0xDEADC0DE;
+
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/progs/test_skeleton.c

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2019 Facebook */
 
+#include <stdbool.h>
 #include <linux/bpf.h>
 #include "bpf_helpers.h"
 
@@ -20,6 +21,10 @@ char out3 = 0;
 long long out4 = 0;
 int out1 = 0;
 
+extern bool CONFIG_BPF_SYSCALL;
+extern int LINUX_KERNEL_VERSION;
+bool bpf_syscall = 0;
+int kern_ver = 0;
 
 SEC("raw_tp/sys_enter")
 int handler(const void *ctx)
@@ -31,6 +36,10 @@ int handler(const void *ctx)
 	out3 = in3;
 	out4 = in4;
 	out5 = in5;
+
+	bpf_syscall = CONFIG_BPF_SYSCALL;
+	kern_ver = LINUX_KERNEL_VERSION;
+
 	return 0;
 }