Pseudo_btf_id is a type of ld_imm insn that associates a btf_id to a ksym so that further dereferences on the ksym can use the BTF info to validate accesses. Internally, when seeing a pseudo_btf_id ld insn, the verifier reads the btf_id stored in the insn[0]'s imm field and marks the dst_reg as PTR_TO_BTF_ID. The btf_id points to a VAR_KIND, which is encoded in btf_vminux by pahole. If the VAR is not of a struct type, the dst reg will be marked as PTR_TO_MEM instead of PTR_TO_BTF_ID and the mem_size is resolved to the size of the VAR's type.
From the VAR btf_id, the verifier can also read the address of the
ksym's corresponding kernel var from kallsyms and use that to fill dst_reg.
Therefore, the proper functionality of pseudo_btf_id depends on (1) kallsyms and (2) the encoding of kernel global VARs in pahole, which should be available since pahole v1.18.
Signed-off-by: Hao Luo haoluo@google.com --- include/linux/btf.h | 15 +++++++++ include/uapi/linux/bpf.h | 38 ++++++++++++++++------ kernel/bpf/btf.c | 15 --------- kernel/bpf/verifier.c | 68 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 112 insertions(+), 24 deletions(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h index 8b81fbb4497c..cee4089e83c0 100644 --- a/include/linux/btf.h +++ b/include/linux/btf.h @@ -107,6 +107,21 @@ static inline bool btf_type_is_func_proto(const struct btf_type *t) return BTF_INFO_KIND(t->info) == BTF_KIND_FUNC_PROTO; }
+static inline bool btf_type_is_var(const struct btf_type *t) +{ + return BTF_INFO_KIND(t->info) == BTF_KIND_VAR; +} + +/* union is only a special case of struct: + * all its offsetof(member) == 0 + */ +static inline bool btf_type_is_struct(const struct btf_type *t) +{ + u8 kind = BTF_INFO_KIND(t->info); + + return kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION; +} + static inline u16 btf_type_vlen(const struct btf_type *t) { return BTF_INFO_VLEN(t->info); diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 0480f893facd..468376f2910b 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -346,18 +346,38 @@ enum bpf_link_type { #define BPF_F_TEST_STATE_FREQ (1U << 3)
/* When BPF ldimm64's insn[0].src_reg != 0 then this can have - * two extensions: - * - * insn[0].src_reg: BPF_PSEUDO_MAP_FD BPF_PSEUDO_MAP_VALUE - * insn[0].imm: map fd map fd - * insn[1].imm: 0 offset into value - * insn[0].off: 0 0 - * insn[1].off: 0 0 - * ldimm64 rewrite: address of map address of map[0]+offset - * verifier type: CONST_PTR_TO_MAP PTR_TO_MAP_VALUE + * the following extensions: + * + * insn[0].src_reg: BPF_PSEUDO_MAP_FD + * insn[0].imm: map fd + * insn[1].imm: 0 + * insn[0].off: 0 + * insn[1].off: 0 + * ldimm64 rewrite: address of map + * verifier type: CONST_PTR_TO_MAP */ #define BPF_PSEUDO_MAP_FD 1 +/* + * insn[0].src_reg: BPF_PSEUDO_MAP_VALUE + * insn[0].imm: map fd + * insn[1].imm: offset into value + * insn[0].off: 0 + * insn[1].off: 0 + * ldimm64 rewrite: address of map[0]+offset + * verifier type: PTR_TO_MAP_VALUE + */ #define BPF_PSEUDO_MAP_VALUE 2 +/* + * insn[0].src_reg: BPF_PSEUDO_BTF_ID + * insn[0].imm: kernel btd id of VAR + * insn[1].imm: 0 + * insn[0].off: 0 + * insn[1].off: 0 + * ldimm64 rewrite: address of the kernel variable + * verifier type: PTR_TO_BTF_ID or PTR_TO_MEM, depending on whether the var + * is struct/union. + */ +#define BPF_PSEUDO_BTF_ID 3
/* when bpf_call->src_reg == BPF_PSEUDO_CALL, bpf_call->imm == pc-relative * offset to another bpf function diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 91afdd4c82e3..b6d8f653afe2 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -353,16 +353,6 @@ static bool btf_type_nosize_or_null(const struct btf_type *t) return !t || btf_type_nosize(t); }
-/* union is only a special case of struct: - * all its offsetof(member) == 0 - */ -static bool btf_type_is_struct(const struct btf_type *t) -{ - u8 kind = BTF_INFO_KIND(t->info); - - return kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION; -} - static bool __btf_type_is_struct(const struct btf_type *t) { return BTF_INFO_KIND(t->info) == BTF_KIND_STRUCT; @@ -373,11 +363,6 @@ static bool btf_type_is_array(const struct btf_type *t) return BTF_INFO_KIND(t->info) == BTF_KIND_ARRAY; }
-static bool btf_type_is_var(const struct btf_type *t) -{ - return BTF_INFO_KIND(t->info) == BTF_KIND_VAR; -} - static bool btf_type_is_datasec(const struct btf_type *t) { return BTF_INFO_KIND(t->info) == BTF_KIND_DATASEC; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ef938f17b944..47badde71f83 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7205,6 +7205,68 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, return 0; }
+/* verify ld_imm64 insn of type PSEUDO_BTF_ID is valid */ +static inline int check_pseudo_btf_id(struct bpf_verifier_env *env, + struct bpf_insn *insn) +{ + struct bpf_reg_state *regs = cur_regs(env); + u32 type, id = insn->imm; + u64 addr; + const char *sym_name; + const struct btf_type *t = btf_type_by_id(btf_vmlinux, id); + + if (!t) { + verbose(env, "%s: invalid btf_id %d\n", __func__, id); + return -ENOENT; + } + + if (insn[1].imm != 0) { + verbose(env, "%s: BPF_PSEUDO_BTF_ID uses reserved fields\n", + __func__); + return -EINVAL; + } + + if (!btf_type_is_var(t)) { + verbose(env, "%s: btf_id %d isn't KIND_VAR\n", __func__, id); + return -EINVAL; + } + + sym_name = btf_name_by_offset(btf_vmlinux, t->name_off); + addr = kallsyms_lookup_name(sym_name); + if (!addr) { + verbose(env, "%s: failed to find the address of symbol '%s'.\n", + __func__, sym_name); + return -ENOENT; + } + + insn[0].imm = (u32)addr; + insn[1].imm = addr >> 32; + mark_reg_known_zero(env, regs, insn->dst_reg); + + type = t->type; + t = btf_type_skip_modifiers(btf_vmlinux, type, NULL); + if (!btf_type_is_struct(t)) { + u32 tsize; + const struct btf_type *ret; + const char *tname; + + /* resolve the type size of ksym. */ + ret = btf_resolve_size(btf_vmlinux, t, &tsize, NULL, NULL); + if (IS_ERR(ret)) { + tname = btf_name_by_offset(btf_vmlinux, t->name_off); + verbose(env, "unable to resolve the size of type '%s': %ld\n", + tname, PTR_ERR(ret)); + return -EINVAL; + } + regs[insn->dst_reg].type = PTR_TO_MEM; + regs[insn->dst_reg].mem_size = tsize; + } else { + regs[insn->dst_reg].type = PTR_TO_BTF_ID; + regs[insn->dst_reg].btf_id = type; + } + return 0; +} + /* verify BPF_LD_IMM64 instruction */ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn) { @@ -7234,6 +7296,9 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn) return 0; }
+ if (insn->src_reg == BPF_PSEUDO_BTF_ID) + return check_pseudo_btf_id(env, insn); + map = env->used_maps[aux->map_index]; mark_reg_known_zero(env, regs, insn->dst_reg); regs[insn->dst_reg].map_ptr = map; @@ -9255,6 +9320,9 @@ static int replace_map_fd_with_map_ptr(struct bpf_verifier_env *env) /* valid generic load 64-bit imm */ goto next_insn;
+ if (insn[0].src_reg == BPF_PSEUDO_BTF_ID) + goto next_insn; + /* In final convert_pseudo_ld_imm64() step, this is * converted into regular 64-bit imm load insn. */