Merge branch 'a-pair-of-follow-ups-for-indirect-jumps'

Anton Protopopov says:

====================
A pair of follow ups for indirect jumps

Two fixes suggested by Alexei in [1]. Resending as a series,
as the second patch depends on the first.

[1] https://lore.kernel.org/bpf/CAADnVQK3piReoo1ja=[e-mail]/#R
====================

Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

kernel/bpf/bpf_insn_array.c

···
 
 	bpf_map_init_from_attr(&insn_array->map, attr);
 
+	/* BPF programs aren't allowed to write to the map */
+	insn_array->map.map_flags |= BPF_F_RDONLY_PROG;
+
 	return &insn_array->map;
 }
 

kernel/bpf/verifier.c

···
 		break;
 	case PTR_TO_MAP_VALUE:
 		pointer_desc = "value ";
+		if (reg->map_ptr->map_type == BPF_MAP_TYPE_INSN_ARRAY)
+			strict = true;
 		break;
 	case PTR_TO_CTX:
 		pointer_desc = "context ";
···
 {
 	struct bpf_reg_state *regs = cur_regs(env);
 	struct bpf_reg_state *reg = regs + regno;
-	bool insn_array = reg->type == PTR_TO_MAP_VALUE &&
-			  reg->map_ptr->map_type == BPF_MAP_TYPE_INSN_ARRAY;
 	int size, err = 0;
 
 	size = bpf_size_to_bytes(bpf_size);
···
 		return size;
 
 	/* alignment checks will add in reg->off themselves */
-	err = check_ptr_alignment(env, reg, off, size, strict_alignment_once || insn_array);
+	err = check_ptr_alignment(env, reg, off, size, strict_alignment_once);
 	if (err)
 		return err;
 
···
 			verbose(env, "R%d leaks addr into map\n", value_regno);
 			return -EACCES;
 		}
-		if (t == BPF_WRITE && insn_array) {
-			verbose(env, "writes into insn_array not allowed\n");
-			return -EACCES;
-		}
-
 		err = check_map_access_type(env, regno, off, size, t);
 		if (err)
 			return err;
···
 		} else if (t == BPF_READ && value_regno >= 0) {
 			struct bpf_map *map = reg->map_ptr;
 
-			/* if map is read-only, track its contents as scalars */
+			/*
+			 * If map is read-only, track its contents as scalars,
+			 * unless it is an insn array (see the special case below)
+			 */
 			if (tnum_is_const(reg->var_off) &&
 			    bpf_map_is_rdonly(map) &&
-			    map->ops->map_direct_value_addr) {
+			    map->ops->map_direct_value_addr &&
+			    map->map_type != BPF_MAP_TYPE_INSN_ARRAY) {
 				int map_off = off + reg->var_off.value;
 				u64 val = 0;
 

tools/testing/selftests/bpf/progs/verifier_gotox.c

···
 }
 
 SEC("socket")
-__failure __msg("writes into insn_array not allowed")
+__failure __msg("write into map forbidden, value_size=16 off=8 size=8")
 __naked void jump_table_no_writes(void)
 {
 	asm volatile ("						\