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([2600:1700:6cf8:1240:3731:e216:7508:9d27]) by smtp.gmail.com with ESMTPSA id o3-20020a817303000000b006040bff8aedsm1216380ywc.110.2024.02.03.16.21.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 03 Feb 2024 16:21:32 -0800 (PST) Message-ID: Date: Sat, 3 Feb 2024 16:21:31 -0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC bpf-next v4 5/6] bpf: Create argument information for nullable arguments. Content-Language: en-US From: Kui-Feng Lee To: Martin KaFai Lau , thinker.li@gmail.com Cc: kuifeng@meta.com, bpf@vger.kernel.org, ast@kernel.org, song@kernel.org, kernel-team@meta.com, andrii@kernel.org, davemarchevsky@meta.com, dvernet@meta.com References: <20240202220516.1165466-1-thinker.li@gmail.com> <20240202220516.1165466-6-thinker.li@gmail.com> <6b1d0822-73c4-472a-a170-947b53f2c66f@linux.dev> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2/2/24 17:57, Kui-Feng Lee wrote: > > > On 2/2/24 16:40, Martin KaFai Lau wrote: >> On 2/2/24 2:05 PM, thinker.li@gmail.com wrote: >>> From: Kui-Feng Lee >>> >>> Collect argument information from the type information of stub >>> functions to >>> mark arguments of BPF struct_ops programs with PTR_MAYBE_NULL if they >>> are >>> nullable.  A nullable argument is annotated by suffixing "__nullable" at >>> the argument name of stub function. >>> >>> For nullable arguments, this patch sets an arg_info to label their >>> reg_type >>> with PTR_TO_BTF_ID | PTR_TRUSTED | PTR_MAYBE_NULL. This makes the >>> verifier >>> to check programs and ensure that they properly check the pointer. The >>> programs should check if the pointer is null before accessing the >>> pointed >>> memory. >>> >>> The implementer of a struct_ops type should annotate the arguments >>> that can >>> be null. The implementer should define a stub function (empty) as a >>> placeholder for each defined operator. The name of a stub function >>> should >>> be in the pattern "__". For example, for >>> test_maybe_null of struct bpf_testmod_ops, it's stub function name >>> should >>> be "bpf_testmod_ops__test_maybe_null". You mark an argument nullable by >>> suffixing the argument name with "__nullable" at the stub function. >>> >>> Since we already has stub functions for kCFI, we just reuse these stub >>> functions with the naming convention mentioned earlier. These stub >>> functions with the naming convention is only required if there are >>> nullable >>> arguments to annotate. For functions having not nullable arguments, stub >>> functions are not necessary for the purpose of this patch. >>> >>> This patch will prepare a list of struct bpf_ctx_arg_aux, aka >>> arg_info, for >>> each member field of a struct_ops type.  "arg_info" will be assigned to >>> "prog->aux->ctx_arg_info" of BPF struct_ops programs in >>> check_struct_ops_btf_id() so that it can be used by btf_ctx_access() >>> later >>> to set reg_type properly for the verifier. >> >> I looked at the high level. Some comments below. >> >>> >>> Signed-off-by: Kui-Feng Lee >>> --- >>>   include/linux/bpf.h         |  17 ++++ >>>   kernel/bpf/bpf_struct_ops.c | 166 ++++++++++++++++++++++++++++++++++-- >>>   kernel/bpf/btf.c            |  14 +++ >>>   kernel/bpf/verifier.c       |   6 ++ >>>   4 files changed, 198 insertions(+), 5 deletions(-) >>> >>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h >>> index 9a2ee9456989..63ef5cbfd213 100644 >>> --- a/include/linux/bpf.h >>> +++ b/include/linux/bpf.h >>> @@ -1709,6 +1709,19 @@ struct bpf_struct_ops { >>>       struct btf_func_model func_models[BPF_STRUCT_OPS_MAX_NR_MEMBERS]; >>>   }; >>> +/* Every member of a struct_ops type has an instance even the member >>> is not >>> + * an operator (function pointer). The "arg_info" field will be >>> assigned to >>> + * prog->aux->arg_info of BPF struct_ops programs to provide the >>> argument >>> + * information required by the verifier to verify the program. >>> + * >>> + * btf_ctx_access() will lookup prog->aux->arg_info to find the >>> + * corresponding entry for an given argument. >>> + */ >>> +struct bpf_struct_ops_member_arg_info { >>> +    struct bpf_ctx_arg_aux *arg_info; >>> +    u32 arg_info_cnt; >>> +}; >>> + >>>   struct bpf_struct_ops_desc { >>>       struct bpf_struct_ops *st_ops; >>> @@ -1716,6 +1729,10 @@ struct bpf_struct_ops_desc { >>>       const struct btf_type *value_type; >>>       u32 type_id; >>>       u32 value_id; >>> + >>> +    /* Collection of argument information for each member */ >>> +    struct bpf_struct_ops_member_arg_info *member_arg_info; >>> +    u32 member_arg_info_cnt; >>>   }; >>>   enum bpf_struct_ops_state { >>> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c >>> index f98f580de77a..313f6ceabcf4 100644 >>> --- a/kernel/bpf/bpf_struct_ops.c >>> +++ b/kernel/bpf/bpf_struct_ops.c >>> @@ -116,17 +116,148 @@ static bool is_valid_value_type(struct btf >>> *btf, s32 value_id, >>>       return true; >>>   } >>> +#define MAYBE_NULL_SUFFIX "__nullable" >>> +#define MAX_STUB_NAME 128 >>> + >>> +static int match_nullable_suffix(const char *name) >>> +{ >>> +    int suffix_len, len; >>> + >>> +    if (!name) >>> +        return 0; >>> + >>> +    suffix_len = sizeof(MAYBE_NULL_SUFFIX) - 1; >>> +    len = strlen(name); >>> +    if (len < suffix_len) >>> +        return 0; >>> + >>> +    return !strcmp(name + len - suffix_len, MAYBE_NULL_SUFFIX); >>> +} >>> + >>> +/* Return the type info of a stub function, if it exists. >>> + * >>> + * The name of the stub function is made up of the name of the >>> struct_ops >>> + * and the name of the function pointer member, separated by "__". For >>> + * example, if the struct_ops is named "foo_ops" and the function >>> pointer >>> + * member is named "bar", the stub function name would be >>> "foo_ops__bar". >>> + */ >>> +static const  struct btf_type * >>> +find_stub_func_proto(struct btf *btf, const char *st_op_name, >>> +             const char *member_name) >>> +{ >>> +    char stub_func_name[MAX_STUB_NAME]; >>> +    const struct btf_type *t, *func_proto; >>> +    s32 btf_id; >>> + >>> +    snprintf(stub_func_name, MAX_STUB_NAME, "%s__%s", >>> +         st_op_name, member_name); >>> +    btf_id = btf_find_by_name_kind(btf, stub_func_name, BTF_KIND_FUNC); >>> +    if (btf_id < 0) >>> +        return NULL; >>> +    t = btf_type_by_id(btf, btf_id); >>> +    if (!t) >>> +        return NULL; >>> +    func_proto = btf_type_by_id(btf, t->type); >>> + >>> +    return func_proto; >>> +} >>> + >>> +/* Prepare argument info for every nullable argument of a member of a >>> + * struct_ops type. >>> + * >>> + * Create and initialize a list of struct >>> bpf_struct_ops_member_arg_info >>> + * according to type info of the arguments of the stub functions. >>> (Check >>> + * kCFI for more information about stub functions.) >>> + * >>> + * Each member in the struct_ops type has a struct >>> + * bpf_struct_ops_member_arg_info to provide an array of struct >>> + * bpf_ctx_arg_aux, which in turn provides the information that used >>> by the >>> + * verifier to check the arguments of the BPF struct_ops program >>> assigned >>> + * to the member. Here, we only care about the arguments that are >>> marked as >>> + * __nullable. >>> + * >>> + * The array of struct bpf_ctx_arg_aux is eventually assigned to >>> + * prog->aux->ctx_arg_info of BPF struct_ops programs and passed to the >>> + * verifier. (See check_struct_ops_btf_id()) >>> + */ >>> +static int prepare_arg_info(struct btf *btf, >>> +                const char *st_ops_name, >>> +                const char *member_name, >>> +                struct bpf_struct_ops_member_arg_info *member_arg_info) >>> +{ >>> +    const struct btf_type *stub_func_proto, *ptr_type; >>> +    struct bpf_ctx_arg_aux *arg_info, *ai_buf = NULL; >>> +    const struct btf_param *args; >>> +    u32 nargs, arg_no = 0; >>> +    const char *arg_name; >>> +    s32 arg_btf_id; >>> + >>> +    stub_func_proto = find_stub_func_proto(btf, st_ops_name, >>> member_name); >>> +    if (!stub_func_proto) >>> +        return 0; >>> + >>> +    nargs = btf_type_vlen(stub_func_proto); >>> +    if (nargs > MAX_BPF_FUNC_REG_ARGS) { >> >> Checking MAX_BPF_FUNC_REG_ARGS on the stub_func_proto may not be the >> right check. It should have been done on the origin func_proto (i.e. >> non-stub) when preparing the func_model in btf_distill_func_proto(). >> Please double check. > > Got it! > >> >> If it needs to do sanity check on nargs of stub_func_proto, a better >> check is to ensure the narg of the stub_func_proto is the same as the >> orig_func_proto instead. This discrepancy probably should have been >> complained by the compiler already but does not harm to check (==) >> here in case the argument type is changed and a force cast is used >> (more below). > > Yes, it should be complained by the compiler. However, we are not sure > if the stub function found is the one assign to .cfi_stubs, or a random > function happening to have a matched name. > >> >>> +        pr_warn("Cannot support #%u args in stub func %s_stub_%s\n", >>> +            nargs, st_ops_name, member_name); >>> +        return -EINVAL; >>> +    } >>> + >>> +    ai_buf = kcalloc(nargs, sizeof(*ai_buf), GFP_KERNEL); >>> +    if (!ai_buf) >>> +        return -ENOMEM; >>> + >>> +    args = btf_params(stub_func_proto); >>> +    for (arg_no = 0; arg_no < nargs; arg_no++) { >>> +        /* Skip arguments that is not suffixed with >>> +         * "__nullable". >>> +         */ >>> +        arg_name = btf_name_by_offset(btf, >>> +                          args[arg_no].name_off); >>> +        if (!match_nullable_suffix(arg_name)) >> >> I have a question/request. >> >> On top of tagging nullable, can we extend the ctx_arg_info idea here >> to allow changing the pointer type? >> >> In particular, take a stub function in bpf_tcp_ca.c: >> >> static u32 bpf_tcp_ca_ssthresh(struct tcp_sock *tp) >> { >>          return 0; >> } >> >> Instead of the "struct sock *sk" argument as defined in the >> tcp_congestion_ops, the stub function uses "struct tcp_sock *tp'. If >> we can reuse the ctx_arg_info idea here, then it can remove the >> existing way of changing the pointer type from >> bpf_tcp_ca_is_valid_access. > > Yes, it can be. We need a way to annotate the argument we want to > override/promote its type, or generate ctx_arg_info for each > argument of a stub function. By the way, should I support it with the "__override"/"__promote" suffix or any better one? > >> >>> +            continue; >>> + >>> +        /* Should be a pointer to struct, array, scalar, or enum */ >>> +        ptr_type = btf_type_resolve_ptr(btf, args[arg_no].type, >>> +                        &arg_btf_id); >>> +        if (!ptr_type || >>> +            (!btf_type_is_struct(ptr_type) && >>> +             !btf_type_is_array(ptr_type) && >>> +             !btf_type_is_scalar(ptr_type) && >>> +             !btf_is_any_enum(ptr_type))) { >>> +            kfree(ai_buf); >>> +            return -EINVAL; >>> +        } >>> + >>> +        /* Fill the information of the new argument */ >>> +        arg_info = ai_buf + member_arg_info->arg_info_cnt++; >>> +        arg_info->reg_type = >>> +            PTR_TRUSTED | PTR_MAYBE_NULL | PTR_TO_BTF_ID; >>> +        arg_info->btf_id = arg_btf_id; >>> +        arg_info->btf = btf; >>> +        arg_info->offset = arg_no * sizeof(u64); >> >> I think for the current struct_ops users should be fine to assume >> sizeof(u64). The current struct_ops users should only have >> pointer/scalar argument (meaning there is no struct passed-by-value >> argument). >> >> I still think it is better to get it correct for all trampoline >> supported argument here. Take a look at 720e6a435194 ("bpf: Allow >> struct argument in trampoline based programs") and get_ctx_arg_idx(). >> It may be > > I will add another function to translate arg_no to offset. > >> easier (not sure if it is cleaner) to directly store the arg_no into >> arg_info here but arg_info only has offset now. Please think about >> what could be a cleaner way to do it. > > The offset here is an offset from the start of a context where > the argument is. The BPF opcode access an argument with it's offset, so > we eventually need to translate the arg_no into the offset. The > difference is translating here or in btf_ctx_access(). > > The question here is "what is OFFSET for?"  Without explanation, it > is hard for people to tell what it is. Maybe, we need to change the its > to ctx_offset or alike. > >> >>> +    } >>> + >>> +    if (!member_arg_info->arg_info_cnt) >>> +        kfree(ai_buf); >>> +    else >>> +        member_arg_info->arg_info = ai_buf; >>> + >>> +    return 0; >>> +} >>> + >>>   int bpf_struct_ops_desc_init(struct bpf_struct_ops_desc *st_ops_desc, >>>                    struct btf *btf, >>>                    struct bpf_verifier_log *log) >>>   { >>> +    struct bpf_struct_ops_member_arg_info *member_arg_info; >>>       struct bpf_struct_ops *st_ops = st_ops_desc->st_ops; >>>       const struct btf_member *member; >>>       const struct btf_type *t; >>>       s32 type_id, value_id; >>>       char value_name[128]; >>>       const char *mname; >>> -    int i; >>> +    int i, err; >>>       if (strlen(st_ops->name) + VALUE_PREFIX_LEN >= >>>           sizeof(value_name)) { >>> @@ -160,6 +291,11 @@ int bpf_struct_ops_desc_init(struct >>> bpf_struct_ops_desc *st_ops_desc, >>>       if (!is_valid_value_type(btf, value_id, t, value_name)) >>>           return -EINVAL; >>> +    member_arg_info = kcalloc(btf_type_vlen(t), >>> sizeof(*member_arg_info), >>> +                  GFP_KERNEL); >>> +    if (!member_arg_info) >>> +        return -ENOMEM; >>> + >>>       for_each_member(i, t, member) { >>>           const struct btf_type *func_proto; >>> @@ -167,13 +303,15 @@ int bpf_struct_ops_desc_init(struct >>> bpf_struct_ops_desc *st_ops_desc, >>>           if (!*mname) { >>>               pr_warn("anon member in struct %s is not supported\n", >>>                   st_ops->name); >>> -            return -EOPNOTSUPP; >>> +            err = -EOPNOTSUPP; >>> +            goto errout; >>>           } >>>           if (__btf_member_bitfield_size(t, member)) { >>>               pr_warn("bit field member %s in struct %s is not >>> supported\n", >>>                   mname, st_ops->name); >>> -            return -EOPNOTSUPP; >>> +            err = -EOPNOTSUPP; >>> +            goto errout; >>>           } >>>           func_proto = btf_type_resolve_func_ptr(btf, >>> @@ -185,14 +323,24 @@ int bpf_struct_ops_desc_init(struct >>> bpf_struct_ops_desc *st_ops_desc, >>>                          &st_ops->func_models[i])) { >>>               pr_warn("Error in parsing func ptr %s in struct %s\n", >>>                   mname, st_ops->name); >>> -            return -EINVAL; >>> +            err = -EINVAL; >>> +            goto errout; >>>           } >>> + >>> +        err = prepare_arg_info(btf, st_ops->name, mname, >>> +                       member_arg_info + i); >>> +        if (err) >>> +            goto errout; >>>       } >>> +    st_ops_desc->member_arg_info = member_arg_info; >>> +    st_ops_desc->member_arg_info_cnt = btf_type_vlen(t); >> >> It should be the same as btf_type_vlen(st_ops_desc->type). I would >> avoid this duplicated info within the same st_ops_desc. > > Will remove it. > >> >>> + >>>       if (st_ops->init(btf)) { >>>           pr_warn("Error in init bpf_struct_ops %s\n", >>>               st_ops->name); >>> -        return -EINVAL; >>> +        err = -EINVAL; >>> +        goto errout; >>>       } >>>       st_ops_desc->type_id = type_id; >>> @@ -201,6 +349,14 @@ int bpf_struct_ops_desc_init(struct >>> bpf_struct_ops_desc *st_ops_desc, >>>       st_ops_desc->value_type = btf_type_by_id(btf, value_id); >>>       return 0; >>> + >>> +errout: >>> +    while (i > 0) >>> +        kfree(member_arg_info[--i].arg_info); >>> +    kfree(member_arg_info); >>> +    st_ops_desc->member_arg_info = NULL; >>> + >>> +    return err; >>>   } >>>   static int bpf_struct_ops_map_get_next_key(struct bpf_map *map, >>> void *key, >>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c >>> index 20d2160b3db5..fd192f69eb78 100644 >>> --- a/kernel/bpf/btf.c >>> +++ b/kernel/bpf/btf.c >>> @@ -1699,6 +1699,20 @@ static void btf_free_struct_meta_tab(struct >>> btf *btf) >>>   static void btf_free_struct_ops_tab(struct btf *btf) >>>   { >>>       struct btf_struct_ops_tab *tab = btf->struct_ops_tab; >>> +    struct bpf_struct_ops_member_arg_info *ma_info; >>> +    int i, j; >>> +    u32 cnt; >>> + >>> +    if (tab) >>> +        for (i = 0; i < tab->cnt; i++) { >>> +            ma_info = tab->ops[i].member_arg_info; >>> +            if (ma_info) { >>> +                cnt = tab->ops[i].member_arg_info_cnt; >>> +                for (j = 0; j < cnt; j++) >>> +                    kfree(ma_info[j].arg_info); >>> +            } >>> +            kfree(ma_info); >>> +        } >>>       kfree(tab); >>>       btf->struct_ops_tab = NULL; >>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >>> index cd4d780e5400..d1d1c2836bc2 100644 >>> --- a/kernel/bpf/verifier.c >>> +++ b/kernel/bpf/verifier.c >>> @@ -20373,6 +20373,12 @@ static int check_struct_ops_btf_id(struct >>> bpf_verifier_env *env) >>>           } >>>       } >>> +    /* btf_ctx_access() used this to provide argument type info */ >>> +    prog->aux->ctx_arg_info = >>> +        st_ops_desc->member_arg_info[member_idx].arg_info; >>> +    prog->aux->ctx_arg_info_size = >>> +        st_ops_desc->member_arg_info[member_idx].arg_info_cnt; >>> + >>>       prog->aux->attach_func_proto = func_proto; >>>       prog->aux->attach_func_name = mname; >>>       env->ops = st_ops->verifier_ops; >>