On Fri, Nov 3, 2023 at 2:46 PM Song Liu <song@xxxxxxxxxx> wrote:
>
> ARG_PTR_TO_CONST_STR is used to specify constant string args for BPF
> helpers. The logic that verifies a reg is ARG_PTR_TO_CONST_STR is
> implemented in check_func_arg().
>
> As we introduce kfuncs with constant string args, it is necessary to
> do the same check for kfuncs (in check_kfunc_args). Factor out the logic
> for ARG_PTR_TO_CONST_STR to a new check_reg_const_str() so that it can be
> reused.
>
> check_func_arg() ensures check_reg_const_str() is only called with reg of
> type PTR_TO_MAP_VALUE. Add a redundent type check in check_reg_const_str()
> to avoid misuse in the future. Other than this redundent check, there is
> no change in behavior.
>
> Signed-off-by: Song Liu <song@xxxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 85 +++++++++++++++++++++++++------------------
> 1 file changed, 49 insertions(+), 36 deletions(-)
>
LGTM. But please double check indentation and tabs vs spaces, just in case.
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 2197385d91dc..fefe3eafccb9 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -8718,6 +8718,54 @@ static enum bpf_dynptr_type dynptr_get_type(struct bpf_verifier_env *env,
> return state->stack[spi].spilled_ptr.dynptr.type;
> }
>
> +static int check_reg_const_str(struct bpf_verifier_env *env,
> + struct bpf_reg_state *reg, u32 regno)
> +{
> + struct bpf_map *map = reg->map_ptr;
> + int err;
> + int map_off;
> + u64 map_addr;
> + char *str_ptr;
> +
> + if (reg->type != PTR_TO_MAP_VALUE)
> + return -EINVAL;
> +
> + if (!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;
indentation is off?
> + }
> +
> + if (!map->ops->map_direct_value_addr) {
> + verbose(env, "no direct value access support for this map type\n");
> + return -EACCES;
same?
> + }
> +
> + err = check_map_access(env, regno, reg->off,
> + map->value_size - reg->off, false,
> + ACCESS_HELPER);
> + 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 0;
> +}
> +
> static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> struct bpf_call_arg_meta *meta,
> const struct bpf_func_proto *fn,
> @@ -8962,44 +9010,9 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
> }
> case ARG_PTR_TO_CONST_STR:
> {
> - struct bpf_map *map = reg->map_ptr;
> - int map_off;
> - u64 map_addr;
> - char *str_ptr;
> -
> - if (!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,
> - ACCESS_HELPER);
> + err = check_reg_const_str(env, reg, regno);
> 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;
> - }
> break;
> }
> case ARG_PTR_TO_KPTR:
> --
> 2.34.1
>
