Add tests that demonstrate the verifier support for deep call stacks while still enforcing maximum stack size limits. Acked-by: Eduard Zingerman Signed-off-by: Emil Tsalapatis --- .../bpf/prog_tests/test_global_funcs.c | 2 + .../bpf/progs/test_global_func_deep_stack.c | 83 +++++++++++++++++++ 2 files changed, 85 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/test_global_func_deep_stack.c diff --git a/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c b/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c index e905cbaf6b3d..500446808908 100644 --- a/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c +++ b/tools/testing/selftests/bpf/prog_tests/test_global_funcs.c @@ -18,6 +18,7 @@ #include "test_global_func15.skel.h" #include "test_global_func16.skel.h" #include "test_global_func17.skel.h" +#include "test_global_func_deep_stack.skel.h" #include "test_global_func_ctx_args.skel.h" #include "bpf/libbpf_internal.h" @@ -155,6 +156,7 @@ void test_test_global_funcs(void) RUN_TESTS(test_global_func15); RUN_TESTS(test_global_func16); RUN_TESTS(test_global_func17); + RUN_TESTS(test_global_func_deep_stack); RUN_TESTS(test_global_func_ctx_args); if (test__start_subtest("ctx_arg_rewrite")) diff --git a/tools/testing/selftests/bpf/progs/test_global_func_deep_stack.c b/tools/testing/selftests/bpf/progs/test_global_func_deep_stack.c new file mode 100644 index 000000000000..733c3334b7b1 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_global_func_deep_stack.c @@ -0,0 +1,83 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Copyright (c) 2026 Meta Platforms, Inc and affiliates. */ +#include +#include +#include "bpf_misc.h" + +/* + * Macro tricks to tersely define for long non-recursive call chains. Add + * computation to the functions prevent tail recursion from reducing the + * stack size to 0. + */ + +#define CAT(a, b) a ## b +#define XCAT(a, b) CAT(a, b) + +#define F_0 \ +__attribute__((noinline)) \ +int f0(unsigned long a) { volatile long b = a + 16; if (a == 0) return 0; return b; } + +#define FN(n, prev) \ +__attribute__((noinline)) \ +int XCAT(f, n)(unsigned long a) { volatile long b = XCAT(f, prev)(a - 1); if (!b) return 0; return b + 1; } + +/* Call chain 33 levels deep. */ +#define F_1 F_0 FN(1, 0) +#define F_2 F_1 FN(2, 1) +#define F_3 F_2 FN(3, 2) +#define F_4 F_3 FN(4, 3) +#define F_5 F_4 FN(5, 4) +#define F_6 F_5 FN(6, 5) +#define F_7 F_6 FN(7, 6) +#define F_8 F_7 FN(8, 7) +#define F_9 F_8 FN(9, 8) +#define F_10 F_9 FN(10, 9) +#define F_11 F_10 FN(11, 10) +#define F_12 F_11 FN(12, 11) +#define F_13 F_12 FN(13, 12) +#define F_14 F_13 FN(14, 13) +#define F_15 F_14 FN(15, 14) +#define F_16 F_15 FN(16, 15) +#define F_17 F_16 FN(17, 16) +#define F_18 F_17 FN(18, 17) +#define F_19 F_18 FN(19, 18) +#define F_20 F_19 FN(20, 19) +#define F_21 F_20 FN(21, 20) +#define F_22 F_21 FN(22, 21) +#define F_23 F_22 FN(23, 22) +#define F_24 F_23 FN(24, 23) +#define F_25 F_24 FN(25, 24) +#define F_26 F_25 FN(26, 25) +#define F_27 F_26 FN(27, 26) +#define F_28 F_27 FN(28, 27) +#define F_29 F_28 FN(29, 28) +#define F_30 F_29 FN(30, 29) +#define F_31 F_30 FN(31, 30) +#define F_32 F_31 FN(32, 31) + +#define CAT2(a, b) a ## b +#define XCAT2(a, b) CAT2(a, b) + +#define F(n) XCAT2(F_, n) + +F(32) + +/* Ensure that even 32 levels deep, the function verifies. */ +SEC("syscall") +__success +int global_func_deep_stack_success(struct __sk_buff *skb) +{ + return f31(55); +} + +/* + * Check we actually honor stack limits (33 * 16 = 528 > 512 = MAX_STACK_DEPTH). + * The stack depth is 16 because the verifier calls round_up_stack_depth() on + * the size. + */ +SEC("syscall") +__failure __msg("combined stack size of 34 calls") +int global_func_deep_stack_fail(struct __sk_buff *skb) +{ + return f32(123); +} -- 2.49.0