diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst index 021be6d93dfb..9c205d8b5fff 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -278,6 +278,33 @@ An example is given below:: ... } +2.3.8 __arena and __arena__nullable Annotations +----------------------------------------------- + +Both annotations indicate that the pointer argument points into the +calling program's arena. The JIT rebases the value at the call site so +the kfunc receives a directly dereferenceable kernel address, subject to +the access rules described in :ref:`BPF_kfunc_arena_access` (at most +``GUARD_SZ / 2``, 32 KiB, past the pointer in a single unchecked access). + +With ``__arena`` the rebase is unconditional and the argument is never +NULL: a value whose lower 32 bits are zero arrives as the arena base +address (arena offset 0). The kfunc must not check the argument for NULL. +With ``__arena__nullable`` such a value arrives as NULL instead and the +kfunc must check before dereferencing. + +An example is given below:: + + __bpf_kfunc int bpf_process_item(struct item *item__arena) + { + ... + } + +Calling such a kfunc requires the program to use an arena map and a JIT with +arena argument support (currently x86-64); verification fails otherwise. The +program can pass any value without compromising the kernel. A value that does +not point into the arena is a program bug. + .. _BPF_kfunc_nodef: 2.4 Using an existing kernel function @@ -522,6 +549,8 @@ In order to accommodate such requirements, the verifier will enforce strict PTR_TO_BTF_ID type matching if two types have the exact same name, with one being suffixed with ``___init``. +.. _BPF_kfunc_arena_access: + 2.8 Accessing arena memory through kfunc arguments -------------------------------------------------- diff --git a/include/linux/bpf.h b/include/linux/bpf.h index d79bf7557ef6..ba1b9d8ac348 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1195,6 +1195,12 @@ struct bpf_prog_offload { /* The argument is signed. */ #define BTF_FMODEL_SIGNED_ARG BIT(1) +/* The argument is an arena pointer. */ +#define BTF_FMODEL_ARENA_ARG BIT(2) + +/* The argument is nullable. */ +#define BTF_FMODEL_NULLABLE_ARG BIT(3) + struct btf_func_model { u8 ret_size; u8 ret_flags; diff --git a/include/linux/filter.h b/include/linux/filter.h index 41b02d53e222..4edba8182db1 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -1214,6 +1214,7 @@ bool bpf_jit_supports_subprog_tailcalls(void); bool bpf_jit_supports_percpu_insn(void); bool bpf_jit_supports_kfunc_call(void); bool bpf_jit_supports_stack_args(void); +bool bpf_jit_supports_arena_args(void); bool bpf_jit_supports_far_kfunc_call(void); bool bpf_jit_supports_exceptions(void); bool bpf_jit_supports_ptr_xchg(void); diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 42414633cf26..4ff6148ae8e8 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -7539,6 +7539,22 @@ static u8 __get_type_fmodel_flags(const struct btf_type *t) return flags; } +static u8 __get_arg_fmodel_flags(const struct btf *btf, + const struct btf_param *arg, + const struct btf_type *t) +{ + u8 flags = __get_type_fmodel_flags(t); + + if (btf_param_match_suffix(btf, arg, "__arena__nullable")) + flags |= BTF_FMODEL_ARENA_ARG | BTF_FMODEL_NULLABLE_ARG; + else if (btf_param_match_suffix(btf, arg, "__arena")) + flags |= BTF_FMODEL_ARENA_ARG; + else if (btf_param_match_suffix(btf, arg, "__nullable")) + flags |= BTF_FMODEL_NULLABLE_ARG; + + return flags; +} + int btf_distill_func_proto(struct bpf_verifier_log *log, struct btf *btf, const struct btf_type *func, @@ -7604,7 +7620,7 @@ int btf_distill_func_proto(struct bpf_verifier_log *log, return -EINVAL; } m->arg_size[i] = ret; - m->arg_flags[i] = __get_type_fmodel_flags(t); + m->arg_flags[i] = __get_arg_fmodel_flags(btf, &args[i], t); } m->nr_args = nargs; return 0; diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index e2076667b245..a3e1fae32eac 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -3308,6 +3308,11 @@ bool __weak bpf_jit_supports_stack_args(void) return false; } +bool __weak bpf_jit_supports_arena_args(void) +{ + return false; +} + bool __weak bpf_jit_supports_far_kfunc_call(void) { return false; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e17084666041..a1b71ac39b3b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10777,7 +10777,8 @@ static bool is_kfunc_arg_refcounted_kptr(const struct btf *btf, const struct btf static bool is_kfunc_arg_nullable(const struct btf *btf, const struct btf_param *arg) { - return btf_param_match_suffix(btf, arg, "__nullable"); + return btf_param_match_suffix(btf, arg, "__nullable") || + btf_param_match_suffix(btf, arg, "__arena"); } static bool is_kfunc_arg_nonown_allowed(const struct btf *btf, const struct btf_param *arg) @@ -10795,6 +10796,12 @@ static bool is_kfunc_arg_irq_flag(const struct btf *btf, const struct btf_param return btf_param_match_suffix(btf, arg, "__irq_flag"); } +static bool is_kfunc_arg_arena(const struct btf *btf, const struct btf_param *arg) +{ + return btf_param_match_suffix(btf, arg, "__arena__nullable") || + btf_param_match_suffix(btf, arg, "__arena"); +} + static bool is_kfunc_arg_scalar_with_name(const struct btf *btf, const struct btf_param *arg, const char *name) @@ -11015,6 +11022,7 @@ enum kfunc_ptr_arg_type { KF_ARG_PTR_TO_IRQ_FLAG, KF_ARG_PTR_TO_RES_SPIN_LOCK, KF_ARG_PTR_TO_TASK_WORK, + KF_ARG_PTR_TO_ARENA, }; enum special_kfunc_type { @@ -11300,7 +11308,6 @@ get_kfunc_arg_type(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta, reg_arg_name(env, argno), btf_type_str(t)); return -EINVAL; } - ref_t = btf_type_skip_modifiers(meta->btf, t->type, NULL); ref_tname = btf_name_by_offset(meta->btf, ref_t->name_off); @@ -11349,7 +11356,30 @@ get_kfunc_arg_type(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta, arg_type = KF_ARG_PTR_TO_RES_SPIN_LOCK; else if (is_kfunc_arg_callback(env, meta->btf, &args[arg])) arg_type = KF_ARG_PTR_TO_CALLBACK; - else if (arg + 1 < nargs && + else if (is_kfunc_arg_arena(meta->btf, &args[arg])) { + if (!bpf_jit_supports_arena_args()) { + verbose(env, "JIT does not support kfunc %s() with arena pointer arguments\n", + meta->func_name); + return -ENOTSUPP; + } + if (!env->prog->aux->arena) { + verbose(env, + "%s arena pointer requires a program with an associated arena\n", + reg_arg_name(env, argno)); + return -EINVAL; + } + if (reg_from_argno(argno) < 0) { + verbose(env, "%s arena pointer cannot be a stack argument\n", + reg_arg_name(env, argno)); + return -EINVAL; + } + /* + * Both suffixes accept a constant zero. The function model determines + * whether the JIT rebases it to the arena base or preserves NULL. + * The common nullable path below records that verifier property. + */ + arg_type = KF_ARG_PTR_TO_ARENA; + } else if (arg + 1 < nargs && (is_kfunc_arg_mem_size(meta->btf, &args[arg + 1]) || is_kfunc_arg_const_mem_size(meta->btf, &args[arg + 1]))) { if (!btf_type_is_void(ref_t) && !btf_type_is_scalar(ref_t) && @@ -12024,7 +12054,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_call_arg_me t = btf_type_skip_modifiers(btf, args[i].type, NULL); if (btf_type_is_ptr(t) && (bpf_register_is_null(reg) || type_may_be_null(reg->type)) && - !is_kfunc_arg_nullable(meta->btf, &args[i])) { + !type_may_be_null(kf_arg_type)) { verbose(env, "Possibly NULL pointer passed to trusted %s\n", reg_arg_name(env, argno)); return -EACCES; @@ -12077,6 +12107,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_call_arg_me case KF_ARG_PTR_TO_TASK_WORK: case KF_ARG_PTR_TO_IRQ_FLAG: case KF_ARG_PTR_TO_RES_SPIN_LOCK: + case KF_ARG_PTR_TO_ARENA: break; case KF_ARG_PTR_TO_DYNPTR: arg_type = ARG_PTR_TO_DYNPTR; @@ -12143,6 +12174,13 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_call_arg_me meta->ret_btf_id = ret; } break; + case KF_ARG_PTR_TO_ARENA: + if (reg->type != PTR_TO_ARENA && reg->type != SCALAR_VALUE) { + verbose(env, "%s is not a pointer to arena or scalar\n", + reg_arg_name(env, argno)); + return -EINVAL; + } + break; case KF_ARG_PTR_TO_ALLOC_BTF_ID: if (reg->type == (PTR_TO_BTF_ID | MEM_ALLOC)) { if (!is_bpf_obj_drop_kfunc(meta->func_id)) {