selftests/bpf: Test access to bpf map pointer

Add selftests to test access to map pointers from bpf program for all
map types except struct_ops (that one would need additional work).

verifier test focuses mostly on scenarios that must be rejected.

prog_tests test focuses on accessing multiple fields both scalar and a
nested struct from bpf program and verifies that those fields have
expected values.
Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/139a6a17f8016491e39347849b951525335c6eb4.1592600985.git.rdna@fb.com

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

+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2020 Facebook
+
+#include <test_progs.h>
+#include <network_helpers.h>
+
+#include "map_ptr_kern.skel.h"
+
+void test_map_ptr(void)
+{
+	struct map_ptr_kern *skel;
+	__u32 duration = 0, retval;
+	char buf[128];
+	int err;
+
+	skel = map_ptr_kern__open_and_load();
+	if (CHECK(!skel, "skel_open_load", "open_load failed\n"))
+		return;
+
+	err = bpf_prog_test_run(bpf_program__fd(skel->progs.cg_skb), 1, &pkt_v4,
+				sizeof(pkt_v4), buf, NULL, &retval, NULL);
+
+	if (CHECK(err, "test_run", "err=%d errno=%d\n", err, errno))
+		goto cleanup;
+
+	if (CHECK(!retval, "retval", "retval=%d map_type=%u line=%u\n", retval,
+		  skel->bss->g_map_type, skel->bss->g_line))
+		goto cleanup;
+
+cleanup:
+	map_ptr_kern__destroy(skel);
+}

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

+{
+	"bpf_map_ptr: read with negative offset rejected",
+	.insns = {
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
+	BPF_LD_MAP_FD(BPF_REG_1, 0),
+	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, -8),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	},
+	.fixup_map_array_48b = { 1 },
+	.result_unpriv = REJECT,
+	.errstr_unpriv = "bpf_array access is allowed only to CAP_PERFMON and CAP_SYS_ADMIN",
+	.result = REJECT,
+	.errstr = "R1 is bpf_array invalid negative access: off=-8",
+},
+{
+	"bpf_map_ptr: write rejected",
+	.insns = {
+	BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
+	BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
+	BPF_LD_MAP_FD(BPF_REG_1, 0),
+	BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_2, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	},
+	.fixup_map_array_48b = { 3 },
+	.result_unpriv = REJECT,
+	.errstr_unpriv = "bpf_array access is allowed only to CAP_PERFMON and CAP_SYS_ADMIN",
+	.result = REJECT,
+	.errstr = "only read from bpf_array is supported",
+},
+{
+	"bpf_map_ptr: read non-existent field rejected",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_6, 0),
+	BPF_LD_MAP_FD(BPF_REG_1, 0),
+	BPF_LDX_MEM(BPF_W, BPF_REG_6, BPF_REG_1, 1),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	},
+	.fixup_map_array_48b = { 1 },
+	.result_unpriv = REJECT,
+	.errstr_unpriv = "bpf_array access is allowed only to CAP_PERFMON and CAP_SYS_ADMIN",
+	.result = REJECT,
+	.errstr = "cannot access ptr member ops with moff 0 in struct bpf_map with off 1 size 4",
+},
+{
+	"bpf_map_ptr: read ops field accepted",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_6, 0),
+	BPF_LD_MAP_FD(BPF_REG_1, 0),
+	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, 0),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	},
+	.fixup_map_array_48b = { 1 },
+	.result_unpriv = REJECT,
+	.errstr_unpriv = "bpf_array access is allowed only to CAP_PERFMON and CAP_SYS_ADMIN",
+	.result = ACCEPT,
+	.retval = 1,
+},