bpf: support instructions arrays with constants blinding

When bpf_jit_harden is enabled, all constants in the BPF code are
blinded to prevent JIT spraying attacks. This happens during JIT
phase. Adjust all the related instruction arrays accordingly.

Signed-off-by: Anton Protopopov <[e-mail]>
Reviewed-by: Eduard Zingerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/core.c

···
 	bpf_prog_clone_free(fp_other);
 }
 
+static void adjust_insn_arrays(struct bpf_prog *prog, u32 off, u32 len)
+{
+#ifdef CONFIG_BPF_SYSCALL
+	struct bpf_map *map;
+	int i;
+
+	if (len <= 1)
+		return;
+
+	for (i = 0; i < prog->aux->used_map_cnt; i++) {
+		map = prog->aux->used_maps[i];
+		if (map->map_type == BPF_MAP_TYPE_INSN_ARRAY)
+			bpf_insn_array_adjust(map, off, len);
+	}
+#endif
+}
+
 struct bpf_prog *bpf_jit_blind_constants(struct bpf_prog *prog)
 {
 	struct bpf_insn insn_buff[16], aux[2];
···
 
 		clone = tmp;
 		insn_delta = rewritten - 1;
+
+		/* Instructions arrays must be updated using absolute xlated offsets */
+		adjust_insn_arrays(clone, prog->aux->subprog_start + i, rewritten);
 
 		/* Walk new program and skip insns we just inserted. */
 		insn = clone->insnsi + i + insn_delta;

kernel/bpf/verifier.c

···
 	struct bpf_insn *insn;
 	void *old_bpf_func;
 	int err, num_exentries;
+	int old_len, subprog_start_adjustment = 0;
 
 	if (env->subprog_cnt <= 1)
 		return 0;
···
 		func[i]->aux->func_idx = i;
 		/* Below members will be freed only at prog->aux */
 		func[i]->aux->btf = prog->aux->btf;
-		func[i]->aux->subprog_start = subprog_start;
+		func[i]->aux->subprog_start = subprog_start + subprog_start_adjustment;
 		func[i]->aux->func_info = prog->aux->func_info;
 		func[i]->aux->func_info_cnt = prog->aux->func_info_cnt;
 		func[i]->aux->poke_tab = prog->aux->poke_tab;
···
 		func[i]->aux->might_sleep = env->subprog_info[i].might_sleep;
 		if (!i)
 			func[i]->aux->exception_boundary = env->seen_exception;
+
+		/*
+		 * To properly pass the absolute subprog start to jit
+		 * all instruction adjustments should be accumulated
+		 */
+		old_len = func[i]->len;
 		func[i] = bpf_int_jit_compile(func[i]);
+		subprog_start_adjustment += func[i]->len - old_len;
+
 		if (!func[i]->jited) {
 			err = -ENOTSUPP;
 			goto out_free;