On Fri, Dec 06, 2024 at 04:36:03PM -0800, Martin KaFai Lau wrote: > On 12/6/24 8:24 AM, Maciej Fijalkowski wrote: > > > I think we can remove the projection_of call from the > > > bpf_is_prog_ctx_type() such that it honors the exact argument > > > type written in the kernel source code. Add this particular projection_of > > > check (renamed to bpf_is_kern_ctx in the diff) to the other callers for > > > backward compat such that the caller can selectively translate > > > the argument of a subprog to the corresponding prog ctx type. > > > > > > Lightly tested only: > > I tried the kernel diff on my side and it addressed my needs. Will you > > send a patch? > > There is no real kfunc taking the "struct sk_buff *" now. It is better to > make this change together with your skb acquire/release kfunc introduction. > You can include this patch in your future set. Ack, good point. Will do as suggested. > > > > > > diff --git i/kernel/bpf/btf.c w/kernel/bpf/btf.c > > > index e7a59e6462a9..2d39f91617fb 100644 > > > --- i/kernel/bpf/btf.c > > > +++ w/kernel/bpf/btf.c > > > @@ -5914,6 +5914,26 @@ bool btf_is_projection_of(const char *pname, const char *tname) > > > return false; > > > } > > > +static bool btf_is_kern_ctx(const struct btf *btf, > > > + const struct btf_type *t, > > > + enum bpf_prog_type prog_type) > > > +{ > > > + const struct btf_type *ctx_type; > > > + const char *tname, *ctx_tname; > > > + > > > + t = btf_type_skip_modifiers(btf, t->type, NULL); > > > + if (!btf_type_is_struct(t)) > > > + return false; > > > + > > > + tname = btf_name_by_offset(btf, t->name_off); > > > + if (!tname) > > > + return false; > > > + > > > + ctx_type = find_canonical_prog_ctx_type(prog_type); > > > + ctx_tname = btf_name_by_offset(btf_vmlinux, ctx_type->name_off); > > > + return btf_is_projection_of(ctx_tname, tname); > > We're sort of doubling the work that btf_is_prog_ctx_type() is doing also, > > maybe add a flag to btf_is_prog_ctx_type() that will allow us to skip > > btf_is_projection_of() call when needed? e.g. in get_kfunc_ptr_arg_type(). > > It is pretty cheap to do the btf_is_kern_ctx(). > > I don't have a strong opinion on either way. may be a "bool check_kern_ctx". It's just that this flow to retrieve both struct names is duplicated, below would serve the same purpose...but I don't have a strong opinion either:) anyways, thanks for discussion! diff --git a/include/linux/btf.h b/include/linux/btf.h index 4214e76c9168..3c6acb993d5b 100644 --- a/include/linux/btf.h +++ b/include/linux/btf.h @@ -577,7 +577,7 @@ struct btf_struct_meta *btf_find_struct_meta(const struct btf *btf, u32 btf_id); bool btf_is_projection_of(const char *pname, const char *tname); bool btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf, const struct btf_type *t, enum bpf_prog_type prog_type, - int arg); + int arg, bool check_proj); int get_kern_ctx_btf_id(struct bpf_verifier_log *log, enum bpf_prog_type prog_type); bool btf_types_are_same(const struct btf *btf1, u32 id1, const struct btf *btf2, u32 id2); @@ -653,7 +653,7 @@ static inline struct btf_struct_meta *btf_find_struct_meta(const struct btf *btf static inline bool btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf, const struct btf_type *t, enum bpf_prog_type prog_type, - int arg) + int arg, bool check_proj) { return false; } diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index e7a59e6462a9..dd27eb35b827 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5916,7 +5916,7 @@ bool btf_is_projection_of(const char *pname, const char *tname) bool btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf, const struct btf_type *t, enum bpf_prog_type prog_type, - int arg) + int arg, bool check_proj) { const struct btf_type *ctx_type; const char *tname, *ctx_tname; @@ -5976,8 +5976,9 @@ bool btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf, * int socket_filter_bpf_prog(struct __sk_buff *skb) * { // no fields of skb are ever used } */ - if (btf_is_projection_of(ctx_tname, tname)) - return true; + if (check_proj) + if (btf_is_projection_of(ctx_tname, tname)) + return true; if (strcmp(ctx_tname, tname)) { /* bpf_user_pt_regs_t is a typedef, so resolve it to * underlying struct and check name again @@ -6140,7 +6141,7 @@ static int btf_translate_to_vmlinux(struct bpf_verifier_log *log, enum bpf_prog_type prog_type, int arg) { - if (!btf_is_prog_ctx_type(log, btf, t, prog_type, arg)) + if (!btf_is_prog_ctx_type(log, btf, t, prog_type, arg, true)) return -ENOENT; return find_kern_ctx_type_id(prog_type); } @@ -7505,7 +7506,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog) if (!btf_type_is_ptr(t)) goto skip_pointer; - if ((tags & ARG_TAG_CTX) || btf_is_prog_ctx_type(log, btf, t, prog_type, i)) { + if ((tags & ARG_TAG_CTX) || btf_is_prog_ctx_type(log, btf, t, prog_type, i, true)) { if (tags & ~ARG_TAG_CTX) { bpf_log(log, "arg#%d has invalid combination of tags\n", i); return -EINVAL; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 60938b136365..bb636f53dfc3 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -11604,7 +11604,8 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env, * type to our caller. When a set of conditions hold in the BTF type of * arguments, we resolve it to a known kfunc_ptr_arg_type. */ - if (btf_is_prog_ctx_type(&env->log, meta->btf, t, resolve_prog_type(env->prog), argno)) + if (btf_is_prog_ctx_type(&env->log, meta->btf, t, resolve_prog_type(env->prog), + argno, false)) return KF_ARG_PTR_TO_CTX; if (is_kfunc_arg_nullable(meta->btf, &args[argno]) && register_is_null(reg)) -- 2.34.1