selftests/bpf: check nullness propagation for reg to reg comparisons

Verify that nullness information is porpagated in the branches of
register to register JEQ and JNE operations.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20221115224859.2452988-3-eddyz87@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

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

+{
+	/* This is equivalent to the following program:
+	 *
+	 *   r6 = skb->sk;
+	 *   r7 = sk_fullsock(r6);
+	 *   r0 = sk_fullsock(r6);
+	 *   if (r0 == 0) return 0;    (a)
+	 *   if (r0 != r7) return 0;   (b)
+	 *   *r7->type;                (c)
+	 *   return 0;
+	 *
+	 * It is safe to dereference r7 at point (c), because of (a) and (b).
+	 * The test verifies that relation r0 == r7 is propagated from (b) to (c).
+	 */
+	"jne/jeq infer not null, PTR_TO_SOCKET_OR_NULL -> PTR_TO_SOCKET for JNE false branch",
+	.insns = {
+	/* r6 = skb->sk; */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, offsetof(struct __sk_buff, sk)),
+	/* if (r6 == 0) return 0; */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 8),
+	/* r7 = sk_fullsock(skb); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
+	BPF_EMIT_CALL(BPF_FUNC_sk_fullsock),
+	BPF_MOV64_REG(BPF_REG_7, BPF_REG_0),
+	/* r0 = sk_fullsock(skb); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
+	BPF_EMIT_CALL(BPF_FUNC_sk_fullsock),
+	/* if (r0 == null) return 0; */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
+	/* if (r0 == r7) r0 = *(r7->type); */
+	BPF_JMP_REG(BPF_JNE, BPF_REG_0, BPF_REG_7, 1), /* Use ! JNE ! */
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_7, offsetof(struct bpf_sock, type)),
+	/* return 0 */
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_CGROUP_SKB,
+	.result = ACCEPT,
+	.result_unpriv = REJECT,
+	.errstr_unpriv = "R7 pointer comparison",
+},
+{
+	/* Same as above, but verify that another branch of JNE still
+	 * prohibits access to PTR_MAYBE_NULL.
+	 */
+	"jne/jeq infer not null, PTR_TO_SOCKET_OR_NULL unchanged for JNE true branch",
+	.insns = {
+	/* r6 = skb->sk */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, offsetof(struct __sk_buff, sk)),
+	/* if (r6 == 0) return 0; */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 9),
+	/* r7 = sk_fullsock(skb); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
+	BPF_EMIT_CALL(BPF_FUNC_sk_fullsock),
+	BPF_MOV64_REG(BPF_REG_7, BPF_REG_0),
+	/* r0 = sk_fullsock(skb); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
+	BPF_EMIT_CALL(BPF_FUNC_sk_fullsock),
+	/* if (r0 == null) return 0; */
+	BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 3),
+	/* if (r0 == r7) return 0; */
+	BPF_JMP_REG(BPF_JNE, BPF_REG_0, BPF_REG_7, 1), /* Use ! JNE ! */
+	BPF_JMP_IMM(BPF_JA, 0, 0, 1),
+	/* r0 = *(r7->type); */
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_7, offsetof(struct bpf_sock, type)),
+	/* return 0 */
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_CGROUP_SKB,
+	.result = REJECT,
+	.errstr = "R7 invalid mem access 'sock_or_null'",
+	.result_unpriv = REJECT,
+	.errstr_unpriv = "R7 pointer comparison",
+},
+{
+	/* Same as a first test, but not null should be inferred for JEQ branch */
+	"jne/jeq infer not null, PTR_TO_SOCKET_OR_NULL -> PTR_TO_SOCKET for JEQ true branch",
+	.insns = {
+	/* r6 = skb->sk; */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, offsetof(struct __sk_buff, sk)),
+	/* if (r6 == null) return 0; */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 9),
+	/* r7 = sk_fullsock(skb); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
+	BPF_EMIT_CALL(BPF_FUNC_sk_fullsock),
+	BPF_MOV64_REG(BPF_REG_7, BPF_REG_0),
+	/* r0 = sk_fullsock(skb); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
+	BPF_EMIT_CALL(BPF_FUNC_sk_fullsock),
+	/* if (r0 == null) return 0; */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 3),
+	/* if (r0 != r7) return 0; */
+	BPF_JMP_REG(BPF_JEQ, BPF_REG_0, BPF_REG_7, 1), /* Use ! JEQ ! */
+	BPF_JMP_IMM(BPF_JA, 0, 0, 1),
+	/* r0 = *(r7->type); */
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_7, offsetof(struct bpf_sock, type)),
+	/* return 0; */
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_CGROUP_SKB,
+	.result = ACCEPT,
+	.result_unpriv = REJECT,
+	.errstr_unpriv = "R7 pointer comparison",
+},
+{
+	/* Same as above, but verify that another branch of JNE still
+	 * prohibits access to PTR_MAYBE_NULL.
+	 */
+	"jne/jeq infer not null, PTR_TO_SOCKET_OR_NULL unchanged for JEQ false branch",
+	.insns = {
+	/* r6 = skb->sk; */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, offsetof(struct __sk_buff, sk)),
+	/* if (r6 == null) return 0; */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 8),
+	/* r7 = sk_fullsock(skb); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
+	BPF_EMIT_CALL(BPF_FUNC_sk_fullsock),
+	BPF_MOV64_REG(BPF_REG_7, BPF_REG_0),
+	/* r0 = sk_fullsock(skb); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_6),
+	BPF_EMIT_CALL(BPF_FUNC_sk_fullsock),
+	/* if (r0 == null) return 0; */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2),
+	/* if (r0 != r7) r0 = *(r7->type); */
+	BPF_JMP_REG(BPF_JEQ, BPF_REG_0, BPF_REG_7, 1), /* Use ! JEQ ! */
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_7, offsetof(struct bpf_sock, type)),
+	/* return 0; */
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_CGROUP_SKB,
+	.result = REJECT,
+	.errstr = "R7 invalid mem access 'sock_or_null'",
+	.result_unpriv = REJECT,
+	.errstr_unpriv = "R7 pointer comparison",
+},
+{
+	/* Maps are treated in a different branch of `mark_ptr_not_null_reg`,
+	 * so separate test for maps case.
+	 */
+	"jne/jeq infer not null, PTR_TO_MAP_VALUE_OR_NULL -> PTR_TO_MAP_VALUE",
+	.insns = {
+	/* r9 = &some stack to use as key */
+	BPF_ST_MEM(BPF_W, BPF_REG_10, -8, 0),
+	BPF_MOV64_REG(BPF_REG_9, BPF_REG_10),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_9, -8),
+	/* r8 = process local map */
+	BPF_LD_MAP_FD(BPF_REG_8, 0),
+	/* r6 = map_lookup_elem(r8, r9); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_8),
+	BPF_MOV64_REG(BPF_REG_2, BPF_REG_9),
+	BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
+	BPF_MOV64_REG(BPF_REG_6, BPF_REG_0),
+	/* r7 = map_lookup_elem(r8, r9); */
+	BPF_MOV64_REG(BPF_REG_1, BPF_REG_8),
+	BPF_MOV64_REG(BPF_REG_2, BPF_REG_9),
+	BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
+	BPF_MOV64_REG(BPF_REG_7, BPF_REG_0),
+	/* if (r6 == 0) return 0; */
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 2),
+	/* if (r6 != r7) return 0; */
+	BPF_JMP_REG(BPF_JNE, BPF_REG_6, BPF_REG_7, 1),
+	/* read *r7; */
+	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_7, offsetof(struct bpf_xdp_sock, queue_id)),
+	/* return 0; */
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.fixup_map_xskmap = { 3 },
+	.prog_type = BPF_PROG_TYPE_XDP,
+	.result = ACCEPT,
+},