selftests/bpf: add tests for the arena offset of globals

Add tests for the new libbpf globals arena offset logic. The
tests cover the case of globals being as large as the arena
itself, and being smaller than the arena. In that case, the
data is placed at the end of the arena, and the beginning
of the arena is free.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>

Author: etsal

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

@@ -6,6 +6,8 @@
 #include "verifier_and.skel.h"
 #include "verifier_arena.skel.h"
 #include "verifier_arena_large.skel.h"
+#include "verifier_arena_globals1.skel.h"
+#include "verifier_arena_globals2.skel.h"
 #include "verifier_array_access.skel.h"
 #include "verifier_async_cb_context.skel.h"
 #include "verifier_basic_stack.skel.h"
@@ -147,6 +149,8 @@ static void run_tests_aux(const char *skel_name,
 void test_verifier_and(void)                  { RUN(verifier_and); }
 void test_verifier_arena(void)                { RUN(verifier_arena); }
 void test_verifier_arena_large(void)          { RUN(verifier_arena_large); }
+void test_verifier_arena_globals1(void)       { RUN(verifier_arena_globals1); }
+void test_verifier_arena_globals2(void)       { RUN(verifier_arena_globals2); }
 void test_verifier_basic_stack(void)          { RUN(verifier_basic_stack); }
 void test_verifier_bitfield_write(void)       { RUN(verifier_bitfield_write); }
 void test_verifier_bounds(void)               { RUN(verifier_bounds); }

tools/testing/selftests/bpf/progs/verifier_arena_globals1.c

@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#define BPF_NO_KFUNC_PROTOTYPES
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_experimental.h"
+#include "bpf_arena_common.h"
+#include "bpf_misc.h"
+
+#define ARENA_PAGES (1UL<< (32 - 12))
+#define GLOBAL_PAGES (16)
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARENA);
+	__uint(map_flags, BPF_F_MMAPABLE);
+	__uint(max_entries, ARENA_PAGES);
+#ifdef __TARGET_ARCH_arm64
+	__ulong(map_extra, (1ull << 32) | (~0u - __PAGE_SIZE * ARENA_PAGES + 1));
+#else
+	__ulong(map_extra, (1ull << 44) | (~0u - __PAGE_SIZE * ARENA_PAGES + 1));
+#endif
+} arena SEC(".maps");
+
+/*
+ * Global data, to be placed at the end of the arena.
+ */
+char __arena global_data[GLOBAL_PAGES][PAGE_SIZE];
+
+SEC("syscall")
+__success __retval(0)
+int check_reserve1(void *ctx)
+{
+#if defined(__BPF_FEATURE_ADDR_SPACE_CAST)
+	__u8 __arena *guard, *globals;
+	int ret;
+
+	guard = (void __arena *)arena_base(&arena);
+	globals = (void __arena *)(arena_base(&arena) + (ARENA_PAGES - GLOBAL_PAGES) * PAGE_SIZE);
+
+	/* Reserve the region we've offset the globals by. */
+	ret = bpf_arena_reserve_pages(&arena, guard, ARENA_PAGES - GLOBAL_PAGES);
+	if (ret)
+		return 1;
+
+	/* Make sure the globals are in the expected offset. */
+	ret = bpf_arena_reserve_pages(&arena, globals, 1);
+	if (!ret)
+		return 2;
+#endif
+	return 0;
+}
+
+/*
+ * Relocation check by reading directly into the global data w/o using symbols.
+ */
+SEC("syscall")
+__success __retval(0)
+int check_relocation(void *ctx)
+{
+#if defined(__BPF_FEATURE_ADDR_SPACE_CAST)
+	const u8 magic = 0xfa;
+	u8 __arena *ptr;
+
+	global_data[GLOBAL_PAGES - 1][PAGE_SIZE / 2] = magic;
+	ptr = (u8 __arena *)((u64)(ARENA_PAGES * PAGE_SIZE - PAGE_SIZE / 2));
+	if (*ptr != magic)
+		return 1;
+
+#endif
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";

tools/testing/selftests/bpf/progs/verifier_arena_globals2.c

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025 Meta Platforms, Inc. and affiliates. */
+
+#define BPF_NO_KFUNC_PROTOTYPES
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+#include "bpf_arena_common.h"
+
+#define ARENA_PAGES (32)
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARENA);
+	__uint(map_flags, BPF_F_MMAPABLE);
+	__uint(max_entries, ARENA_PAGES);
+#ifdef __TARGET_ARCH_arm64
+	__ulong(map_extra, (1ull << 32) | (~0u - __PAGE_SIZE * ARENA_PAGES + 1));
+#else
+	__ulong(map_extra, (1ull << 44) | (~0u - __PAGE_SIZE * ARENA_PAGES + 1));
+#endif
+} arena SEC(".maps");
+
+/*
+ * Fill the entire arena with global data.
+ * The offset into the arena should be 0.
+ */
+char __arena global_data[PAGE_SIZE][ARENA_PAGES];
+
+SEC("syscall")
+__success __retval(0)
+int check_reserve2(void *ctx)
+{
+#if defined(__BPF_FEATURE_ADDR_SPACE_CAST)
+	void __arena *guard;
+	int ret;
+
+	guard = (void __arena *)arena_base(&arena);
+
+	/* Make sure the data at offset 0 case is properly handled. */
+	ret = bpf_arena_reserve_pages(&arena, guard, 1);
+	if (!ret)
+		return 1;
+#endif
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";