Recently, verifier gained __user annotation support [0] where it prevents BPF program from normally derefering user memory pointer in the kernel, and instead requires use of bpf_probe_read_user. We can allow the user to also store these pointers in BPF maps, with the logic that whenever user loads it from the BPF map, it gets marked as MEM_USER. [0]: https://lore.kernel.org/bpf/20220127154555.650886-1-yhs@xxxxxx Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> --- include/linux/bpf.h | 1 + kernel/bpf/btf.c | 20 +++++++++++++++----- kernel/bpf/verifier.c | 21 +++++++++++++++------ 3 files changed, 31 insertions(+), 11 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 843c8c01cf9d..37ca92f4c7b7 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -163,6 +163,7 @@ enum { enum { BPF_MAP_VALUE_OFF_F_REF = (1U << 0), BPF_MAP_VALUE_OFF_F_PERCPU = (1U << 1), + BPF_MAP_VALUE_OFF_F_USER = (1U << 2), }; struct bpf_map_value_off_desc { diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index eb57584ee0a8..bafceae90c32 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -3146,7 +3146,7 @@ static s32 btf_find_by_name_kind_all(const char *name, u32 kind, struct btf **bt static int btf_find_field_kptr(const struct btf *btf, const struct btf_type *t, u32 off, int sz, void *data) { - bool btf_id_tag = false, ref_tag = false, percpu_tag = false; + bool btf_id_tag = false, ref_tag = false, percpu_tag = false, user_tag = false; struct bpf_map_value_off *tab; struct bpf_map *map = data; int nr_off, ret, flags = 0; @@ -3181,6 +3181,13 @@ static int btf_find_field_kptr(const struct btf *btf, const struct btf_type *t, goto end; } percpu_tag = true; + } else if (!strcmp("kernel.bpf.user", __btf_name_by_offset(btf, t->name_off))) { + /* repeated tag */ + if (user_tag) { + ret = -EINVAL; + goto end; + } + user_tag = true; } else if (!strncmp("kernel.", __btf_name_by_offset(btf, t->name_off), sizeof("kernel.") - 1)) { /* TODO: Should we reject these when loading BTF? */ @@ -3192,15 +3199,16 @@ static int btf_find_field_kptr(const struct btf *btf, const struct btf_type *t, t = btf_type_by_id(btf, t->type); } if (!btf_id_tag) { - /* 'ref' or 'percpu' tag must be specified together with 'btf_id' tag */ - if (ref_tag || percpu_tag) { + /* 'ref', 'percpu', 'user' tag must be specified together with 'btf_id' tag */ + if (ref_tag || percpu_tag || user_tag) { ret = -EINVAL; goto end; } return 0; } - /* referenced percpu btf_id pointer is not yet supported */ - if (ref_tag && percpu_tag) { + /* All three are mutually exclusive */ + ret = ref_tag + percpu_tag + user_tag; + if (ret > 1) { ret = -EINVAL; goto end; } @@ -3257,6 +3265,8 @@ static int btf_find_field_kptr(const struct btf *btf, const struct btf_type *t, flags |= BPF_MAP_VALUE_OFF_F_REF; else if (percpu_tag) flags |= BPF_MAP_VALUE_OFF_F_PERCPU; + else if (user_tag) + flags |= BPF_MAP_VALUE_OFF_F_USER; tab->off[nr_off].offset = off; tab->off[nr_off].btf_id = id; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 00d6ab49033d..28da858bb921 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3482,7 +3482,11 @@ static int map_ptr_to_btf_id_match_type(struct bpf_verifier_env *env, enum bpf_reg_type reg_type; const char *reg_name = ""; - if (off_desc->flags & BPF_MAP_VALUE_OFF_F_PERCPU) { + if (off_desc->flags & BPF_MAP_VALUE_OFF_F_USER) { + if (reg->type != (PTR_TO_BTF_ID | MEM_USER) && + reg->type != (PTR_TO_BTF_ID | PTR_MAYBE_NULL | MEM_USER)) + goto end; + } else if (off_desc->flags & BPF_MAP_VALUE_OFF_F_PERCPU) { if (reg->type != PTR_TO_PERCPU_BTF_ID && reg->type != (PTR_TO_PERCPU_BTF_ID | PTR_MAYBE_NULL)) goto end; @@ -3536,7 +3540,9 @@ static int map_ptr_to_btf_id_match_type(struct bpf_verifier_env *env, return 0; end: - if (off_desc->flags & BPF_MAP_VALUE_OFF_F_PERCPU) + if (off_desc->flags & BPF_MAP_VALUE_OFF_F_USER) + reg_type = PTR_TO_BTF_ID | PTR_MAYBE_NULL | MEM_USER; + else if (off_desc->flags & BPF_MAP_VALUE_OFF_F_PERCPU) reg_type = PTR_TO_PERCPU_BTF_ID | PTR_MAYBE_NULL; else reg_type = PTR_TO_BTF_ID | PTR_MAYBE_NULL; @@ -3556,14 +3562,14 @@ static int check_map_ptr_to_btf_id(struct bpf_verifier_env *env, u32 regno, int struct bpf_reg_state *atomic_load_reg) { struct bpf_reg_state *reg = reg_state(env, regno), *val_reg; + bool ref_ptr = false, percpu_ptr = false, user_ptr = false; struct bpf_insn *insn = &env->prog->insnsi[insn_idx]; enum bpf_reg_type reg_type = PTR_TO_BTF_ID; - bool ref_ptr = false, percpu_ptr = false; struct bpf_map_value_off_desc *off_desc; int insn_class = BPF_CLASS(insn->code); + int ret, reg_flags = PTR_MAYBE_NULL; struct bpf_map *map = reg->map_ptr; u32 ref_obj_id = 0; - int ret; /* Things we already checked for in check_map_access: * - Reject cases where variable offset may touch BTF ID pointer @@ -3590,8 +3596,11 @@ static int check_map_ptr_to_btf_id(struct bpf_verifier_env *env, u32 regno, int ref_ptr = off_desc->flags & BPF_MAP_VALUE_OFF_F_REF; percpu_ptr = off_desc->flags & BPF_MAP_VALUE_OFF_F_PERCPU; + user_ptr = off_desc->flags & BPF_MAP_VALUE_OFF_F_USER; if (percpu_ptr) reg_type = PTR_TO_PERCPU_BTF_ID; + else if (user_ptr) + reg_flags |= MEM_USER; if (is_xchg_insn(insn)) { /* We do checks and updates during register fill call for fetch case */ @@ -3623,7 +3632,7 @@ static int check_map_ptr_to_btf_id(struct bpf_verifier_env *env, u32 regno, int } /* val_reg might be NULL at this point */ mark_btf_ld_reg(env, cur_regs(env), value_regno, reg_type, off_desc->btf, - off_desc->btf_id, PTR_MAYBE_NULL); + off_desc->btf_id, reg_flags); /* __mark_ptr_or_null_regs needs ref_obj_id == id to clear * reference state for ptr == NULL branch. */ @@ -3641,7 +3650,7 @@ static int check_map_ptr_to_btf_id(struct bpf_verifier_env *env, u32 regno, int * value from map as PTR_TO_BTF_ID, with the correct type. */ mark_btf_ld_reg(env, cur_regs(env), value_regno, reg_type, off_desc->btf, - off_desc->btf_id, PTR_MAYBE_NULL); + off_desc->btf_id, reg_flags); val_reg->id = ++env->id_gen; } else if (insn_class == BPF_STX) { if (WARN_ON_ONCE(value_regno < 0)) -- 2.35.1
