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bpf: Add a ARG_PTR_TO_CONST_STR argument type

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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 <revest@chromium.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210419155243.1632274-3-revest@chromium.org
This commit is contained in:
Florent Revest 2021-04-19 17:52:39 +02:00 committed by Alexei Starovoitov
parent d9c9e4db18
commit fff13c4bb6
2 changed files with 42 additions and 0 deletions
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1
include/linux/bpf.h
View File

@ -309,6 +309,7 @@ enum bpf_arg_type {
ARG_PTR_TO_PERCPU_BTF_ID, /* pointer to in-kernel percpu 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_FUNC, /* pointer to a bpf program function */
ARG_PTR_TO_STACK_OR_NULL, /* pointer to stack or NULL */ 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, __BPF_ARG_TYPE_MAX,
}; };

41
kernel/bpf/verifier.c
View File

@ -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 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 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 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] = { static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
[ARG_PTR_TO_MAP_KEY] = &map_key_value_types, [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_PERCPU_BTF_ID] = &percpu_btf_ptr_types,
[ARG_PTR_TO_FUNC] = &func_ptr_types, [ARG_PTR_TO_FUNC] = &func_ptr_types,
[ARG_PTR_TO_STACK_OR_NULL] = &stack_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, static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
@ -5067,6 +5069,45 @@ skip_type_check:
if (err) if (err)
return err; return err;
err = check_ptr_alignment(env, reg, 0, size, true); 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; return err;