Re: [PATCH 4/9] bpf: Allow nested BTF object to be refferenced by BTF object + offset
From: Andrii Nakryiko <hidden>
Date: 2020-05-14 22:32:42
Also in:
bpf
On Wed, May 6, 2020 at 6:31 AM Jiri Olsa [off-list ref] wrote:
quoted hunk ↗ jump to hunk
Adding btf_struct_address function that takes 2 BTF objects and offset as arguments and checks wether object A is nested in object B on given offset. This function is be used when checking the helper function PTR_TO_BTF_ID arguments. If the argument has an offset value, the btf_struct_address will check if the final address is the expected BTF ID. This way we can access nested BTF objects under PTR_TO_BTF_ID pointer type and pass them to helpers, while they still point to valid kernel BTF objects. Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- include/linux/bpf.h | 3 ++ kernel/bpf/btf.c | 69 +++++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 32 +++++++++++++------- 3 files changed, 94 insertions(+), 10 deletions(-)diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 1262ec460ab3..bc589cdd8c34 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h@@ -1213,6 +1213,9 @@ int btf_struct_access(struct bpf_verifier_log *log, const struct btf_type *t, int off, int size, enum bpf_access_type atype, u32 *next_btf_id); +int btf_struct_address(struct bpf_verifier_log *log, + const struct btf_type *t, + u32 off, u32 exp_id); int btf_resolve_helper_id(struct bpf_verifier_log *log, const struct bpf_func_proto *fn, int);diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index a2cfba89a8e1..07f22469acab 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c@@ -4004,6 +4004,75 @@ int btf_struct_access(struct bpf_verifier_log *log, return -EINVAL; } +int btf_struct_address(struct bpf_verifier_log *log, + const struct btf_type *t, + u32 off, u32 exp_id)
The logic in this function is quite tricky and overlaps heavily with btf_struct_access. You are already missing flexible array support that Yonghong added recently. Let's see if it's possible to extract all this "find field in a struct by offset" logic into reusable function?
+{
+ u32 i, moff, mtrue_end, msize = 0;
+ const struct btf_member *member;
+ const struct btf_type *mtype;
+ const char *tname, *mname;
+
+again:
+ tname = __btf_name_by_offset(btf_vmlinux, t->name_off);
+ if (!btf_type_is_struct(t)) {
+ bpf_log(log, "Type '%s' is not a struct\n", tname);
+ return -EINVAL;
+ }
+
+ if (off > t->size) {=, actually?
+ bpf_log(log, "address beyond struct %s at off %u size %u\n", + tname, off, t->size); + return -EACCES; + } +
[...]
quoted hunk ↗ jump to hunk
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 70ad009577f8..b988df5ada20 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c@@ -3665,6 +3665,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno, { struct bpf_reg_state *regs = cur_regs(env), *reg = ®s[regno]; enum bpf_reg_type expected_type, type = reg->type; + const struct btf_type *btf_type; int err = 0; if (arg_type == ARG_DONTCARE)@@ -3743,17 +3744,28 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno, expected_type = PTR_TO_BTF_ID; if (type != expected_type) goto err_type; - if (reg->btf_id != meta->btf_id) { - verbose(env, "Helper has type %s got %s in R%d\n", - kernel_type_name(meta->btf_id), - kernel_type_name(reg->btf_id), regno); + if (reg->off) {
well, off==0 can still point to (arbitrarily) nested structs that are first member of outer struct... So I guess it would be better to search for inner struct if btf_id is unexpected regardless of off value?
+ btf_type = btf_type_by_id(btf_vmlinux, reg->btf_id);
+ if (btf_struct_address(&env->log, btf_type, reg->off, meta->btf_id)) {
+ verbose(env, "Helper has type %s got %s in R%d, off %d\n",
+ kernel_type_name(meta->btf_id),
+ kernel_type_name(reg->btf_id), regno, reg->off);
- return -EACCES;
- }
- if (!tnum_is_const(reg->var_off) || reg->var_off.value || reg->off) {
- verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
- regno);
- return -EACCES;
+ return -EACCES;
+ }
+ } else {
+ if (reg->btf_id != meta->btf_id) {
+ verbose(env, "Helper has type %s got %s in R%d\n",
+ kernel_type_name(meta->btf_id),
+ kernel_type_name(reg->btf_id), regno);
+
+ return -EACCES;
+ }
+ if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
+ verbose(env, "R%d is a pointer to in-kernel struct with non-zero offset\n",
+ regno);
+ return -EACCES;
+ }
}
} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
if (meta->func_id == BPF_FUNC_spin_lock) {
--
2.25.4