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([2600:1700:6cf8:1240:b98b:e4f8:58e3:c2f]) by smtp.gmail.com with ESMTPSA id y194-20020a0dd6cb000000b0060418fc78eesm732686ywd.80.2024.02.02.17.57.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 02 Feb 2024 17:57:30 -0800 (PST) Message-ID: Date: Fri, 2 Feb 2024 17:57:28 -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 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> From: Kui-Feng Lee In-Reply-To: <6b1d0822-73c4-472a-a170-947b53f2c66f@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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. > >> +            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; >