selftests/bpf: synthetic tests to push verifier limits

Add a test to generate 1m ld_imm64 insns to stress the verifier.

Bump the size of fill_ld_abs_vlan_push_pop test from 4k to 29k
and jump_around_ld_abs from 4k to 5.5k.
Larger sizes are not possible due to 16-bit offset encoding
in jump instructions.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/test_verifier.c

@@ -50,6 +50,7 @@
 #include "../../../include/linux/filter.h"
 
 #define MAX_INSNS	BPF_MAXINSNS
+#define MAX_TEST_INSNS	1000000
 #define MAX_FIXUPS	8
 #define MAX_NR_MAPS	14
 #define MAX_TEST_RUNS	8
@@ -66,6 +67,7 @@ static int skips;
 struct bpf_test {
 	const char *descr;
 	struct bpf_insn	insns[MAX_INSNS];
+	struct bpf_insn	*fill_insns;
 	int fixup_map_hash_8b[MAX_FIXUPS];
 	int fixup_map_hash_48b[MAX_FIXUPS];
 	int fixup_map_hash_16b[MAX_FIXUPS];
@@ -83,6 +85,7 @@ struct bpf_test {
 	const char *errstr;
 	const char *errstr_unpriv;
 	uint32_t retval, retval_unpriv, insn_processed;
+	int prog_len;
 	enum {
 		UNDEF,
 		ACCEPT,
@@ -119,10 +122,11 @@ struct other_val {
 
 static void bpf_fill_ld_abs_vlan_push_pop(struct bpf_test *self)
 {
-	/* test: {skb->data[0], vlan_push} x 68 + {skb->data[0], vlan_pop} x 68 */
+	/* test: {skb->data[0], vlan_push} x 51 + {skb->data[0], vlan_pop} x 51 */
 #define PUSH_CNT 51
-	unsigned int len = BPF_MAXINSNS;
-	struct bpf_insn *insn = self->insns;
+	/* jump range is limited to 16 bit. PUSH_CNT of ld_abs needs room */
+	unsigned int len = (1 << 15) - PUSH_CNT * 2 * 5 * 6;
+	struct bpf_insn *insn = self->fill_insns;
 	int i = 0, j, k = 0;
 
 	insn[i++] = BPF_MOV64_REG(BPF_REG_6, BPF_REG_1);
@@ -156,12 +160,14 @@ static void bpf_fill_ld_abs_vlan_push_pop(struct bpf_test *self)
 	for (; i < len - 1; i++)
 		insn[i] = BPF_ALU32_IMM(BPF_MOV, BPF_REG_0, 0xbef);
 	insn[len - 1] = BPF_EXIT_INSN();
+	self->prog_len = len;
 }
 
 static void bpf_fill_jump_around_ld_abs(struct bpf_test *self)
 {
-	struct bpf_insn *insn = self->insns;
-	unsigned int len = BPF_MAXINSNS;
+	struct bpf_insn *insn = self->fill_insns;
+	/* jump range is limited to 16 bit. every ld_abs is replaced by 6 insns */
+	unsigned int len = (1 << 15) / 6;
 	int i = 0;
 
 	insn[i++] = BPF_MOV64_REG(BPF_REG_6, BPF_REG_1);
@@ -171,11 +177,12 @@ static void bpf_fill_jump_around_ld_abs(struct bpf_test *self)
 	while (i < len - 1)
 		insn[i++] = BPF_LD_ABS(BPF_B, 1);
 	insn[i] = BPF_EXIT_INSN();
+	self->prog_len = i + 1;
 }
 
 static void bpf_fill_rand_ld_dw(struct bpf_test *self)
 {
-	struct bpf_insn *insn = self->insns;
+	struct bpf_insn *insn = self->fill_insns;
 	uint64_t res = 0;
 	int i = 0;
 
@@ -193,6 +200,7 @@ static void bpf_fill_rand_ld_dw(struct bpf_test *self)
 	insn[i++] = BPF_ALU64_IMM(BPF_RSH, BPF_REG_1, 32);
 	insn[i++] = BPF_ALU64_REG(BPF_XOR, BPF_REG_0, BPF_REG_1);
 	insn[i] = BPF_EXIT_INSN();
+	self->prog_len = i + 1;
 	res ^= (res >> 32);
 	self->retval = (uint32_t)res;
 }
@@ -520,8 +528,10 @@ static void do_test_fixup(struct bpf_test *test, enum bpf_prog_type prog_type,
 	int *fixup_percpu_cgroup_storage = test->fixup_percpu_cgroup_storage;
 	int *fixup_map_spin_lock = test->fixup_map_spin_lock;
 
-	if (test->fill_helper)
+	if (test->fill_helper) {
+		test->fill_insns = calloc(MAX_TEST_INSNS, sizeof(struct bpf_insn));
 		test->fill_helper(test);
+	}
 
 	/* Allocating HTs with 1 elem is fine here, since we only test
 	 * for verifier and not do a runtime lookup, so the only thing
@@ -718,12 +728,17 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 		prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
 	fixup_skips = skips;
 	do_test_fixup(test, prog_type, prog, map_fds);
+	if (test->fill_insns) {
+		prog = test->fill_insns;
+		prog_len = test->prog_len;
+	} else {
+		prog_len = probe_filter_length(prog);
+	}
 	/* If there were some map skips during fixup due to missing bpf
 	 * features, skip this test.
 	 */
 	if (fixup_skips != skips)
 		return;
-	prog_len = probe_filter_length(prog);
 
 	pflags = 0;
 	if (test->flags & F_LOAD_WITH_STRICT_ALIGNMENT)
@@ -731,7 +746,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 	if (test->flags & F_NEEDS_EFFICIENT_UNALIGNED_ACCESS)
 		pflags |= BPF_F_ANY_ALIGNMENT;
 	fd_prog = bpf_verify_program(prog_type, prog, prog_len, pflags,
-				     "GPL", 0, bpf_vlog, sizeof(bpf_vlog), 1);
+				     "GPL", 0, bpf_vlog, sizeof(bpf_vlog), 4);
 	if (fd_prog < 0 && !bpf_probe_prog_type(prog_type, 0)) {
 		printf("SKIP (unsupported program type %d)\n", prog_type);
 		skips++;
@@ -830,6 +845,8 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
 		goto fail_log;
 	}
 close_fds:
+	if (test->fill_insns)
+		free(test->fill_insns);
 	close(fd_prog);
 	for (i = 0; i < MAX_NR_MAPS; i++)
 		close(map_fds[i]);

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

@@ -34,3 +34,12 @@
 	.result = ACCEPT,
 	.retval = 5,
 },
+{
+	"ld_dw: xor semi-random 64 bit imms, test 5",
+	.insns = { },
+	.data = { },
+	.fill_helper = bpf_fill_rand_ld_dw,
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.result = ACCEPT,
+	.retval = 1000000 - 6,
+},