bpf: Add a ARG_PTR_TO_CONST_STR argument type

This type provides the guarantee that an argument is going to be a const pointer to somewhere in a read-only map value. It also checks that this pointer is followed by a zero character before the end of the map value. Signed-off-by: Florent Revest <[email protected]> Signed-off-by: Alexei Starovoitov <[email protected]> Acked-by: Andrii Nakryiko <[email protected]> Link: https://lore.kernel.org/bpf/[email protected]
torvalds · Apr 19, 2021 · fff13c4 · fff13c4
1 parent d9c9e4d
commit fff13c4
Show file tree

Hide file tree

Showing 2 changed files with 42 additions and 0 deletions.
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
@@ -309,6 +309,7 @@ enum bpf_arg_type {
  ARG_PTR_TO_PERCPU_BTF_ID, /* pointer to in-kernel percpu type */
  ARG_PTR_TO_FUNC, /* pointer to a bpf program function */
  ARG_PTR_TO_STACK_OR_NULL, /* pointer to stack or NULL */
+ ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */
  __BPF_ARG_TYPE_MAX,
 };
 

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
@@ -4787,6 +4787,7 @@ static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALU
 static const struct bpf_reg_types percpu_btf_ptr_types = { .types = { PTR_TO_PERCPU_BTF_ID } };
 static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC } };
 static const struct bpf_reg_types stack_ptr_types = { .types = { PTR_TO_STACK } };
+static const struct bpf_reg_types const_str_ptr_types = { .types = { PTR_TO_MAP_VALUE } };
 
 static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
  [ARG_PTR_TO_MAP_KEY] = &map_key_value_types,
@@ -4817,6 +4818,7 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
  [ARG_PTR_TO_PERCPU_BTF_ID] = &percpu_btf_ptr_types,
  [ARG_PTR_TO_FUNC] = &func_ptr_types,
  [ARG_PTR_TO_STACK_OR_NULL] = &stack_ptr_types,
+ [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types,
 };
 
 static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
@@ -5067,6 +5069,45 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
  if (err)
  return err;
  err = check_ptr_alignment(env, reg, 0, size, true);
+ } else if (arg_type == ARG_PTR_TO_CONST_STR) {
+ struct bpf_map *map = reg->map_ptr;
+ int map_off;
+ u64 map_addr;
+ char *str_ptr;
+
+ if (reg->type != PTR_TO_MAP_VALUE || !map ||
+ !bpf_map_is_rdonly(map)) {
+ verbose(env, "R%d does not point to a readonly map'\n", regno);
+ return -EACCES;
+ }
+
+ if (!tnum_is_const(reg->var_off)) {
+ verbose(env, "R%d is not a constant address'\n", regno);
+ return -EACCES;
+ }
+
+ if (!map->ops->map_direct_value_addr) {
+ verbose(env, "no direct value access support for this map type\n");
+ return -EACCES;
+ }
+
+ err = check_map_access(env, regno, reg->off,
+ map->value_size - reg->off, false);
+ if (err)
+ return err;
+
+ map_off = reg->off + reg->var_off.value;
+ err = map->ops->map_direct_value_addr(map, &map_addr, map_off);
+ if (err) {
+ verbose(env, "direct value access on string failed\n");
+ return err;
+ }
+
+ str_ptr = (char *)(long)(map_addr);
+ if (!strnchr(str_ptr + map_off, map->value_size - map_off, 0)) {
+ verbose(env, "string is not zero-terminated\n");
+ return -EINVAL;
+ }
  }
 
  return err;