| Message ID | 20250412170626.3638516-1-kafai.wan@hotmail.com |
|---|---|
| Headers | show |
| Series | bpf: Allow access to const void pointer arguments in tracing programs | expand |
On Mon, Apr 14, 2025 at 6:35 PM Jiri Olsa <olsajiri@gmail.com> wrote: > > On Sun, Apr 13, 2025 at 01:06:25AM +0800, KaFai Wan wrote: > > Adding support to access arguments with const void pointer arguments > > in tracing programs. > > > > Currently we allow tracing programs to access void pointers. If we try to > > access argument which is pointer to const void like 2nd argument in kfree, > > verifier will fail to load the program with; > > > > 0: R1=ctx() R10=fp0 > > ; asm volatile ("r2 = *(u64 *)(r1 + 8); "); > > 0: (79) r2 = *(u64 *)(r1 +8) > > func 'kfree' arg1 type UNKNOWN is not a struct > > > > Adding is_void_ptr to generic void pointer check. > > > > Cc: Leon Hwang <leon.hwang@linux.dev> > > Signed-off-by: KaFai Wan <kafai.wan@hotmail.com> > > --- > > kernel/bpf/btf.c | 10 +++++++++- > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > > index 16ba36f34dfa..e11d3afd0562 100644 > > --- a/kernel/bpf/btf.c > > +++ b/kernel/bpf/btf.c > > @@ -6383,6 +6383,14 @@ struct btf *bpf_prog_get_target_btf(const struct bpf_prog *prog) > > return prog->aux->attach_btf; > > } > > > > +static bool is_void_ptr(struct btf *btf, const struct btf_type *t) > > +{ > > + /* skip modifiers */ > > + t = btf_type_skip_modifiers(btf, t->type, NULL); > > + > > + return t->type == 0; > > I think you can use btf_type_is_void in here > Yes, I will use btf_type_is_void. > > +} > > + > > static bool is_int_ptr(struct btf *btf, const struct btf_type *t) > > { > > /* skip modifiers */ > > @@ -6776,7 +6784,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type, > > } > > } > > > > - if (t->type == 0) > > + if (is_void_ptr(btf, t)) > > lgtm, > > nit, the is_void_ptr name suggest there's also ptr check in the helper function, > which is not the case. I understand it follows is_int_ptr name, but perhaps we > could rename both helpers to is_void and is_int ... feel free to ignore ;-) you are right, I will rename it. but I'm not sure if it's possible to merge these two functions into one like is_void_or_int, they both skip modifiers. > > jirka > > > > /* This is a pointer to void. > > * It is the same as scalar from the verifier safety pov. > > * No further pointer walking is allowed. > > -- > > 2.43.0 > > thanks, kafai
hi, Tracing programs can access arguments via BTF [1]. Currently we allow tracing programs to access pointers to string (char pointer), void pointers, pointers to structs, and int pointers [2]. If we try to access argument which is pointer to const void like 2nd argument in kfree, it's an UNKNOWN type, verifier will fail to load. typedef void (*btf_trace_kfree)(void *, long unsigned int, const void *); [1] https://lore.kernel.org/bpf/20191016032505.2089704-7-ast@kernel.org/ [2] https://lore.kernel.org/bpf/20211208193245.172141-1-jolsa@kernel.org/ --- KaFai Wan (2): bpf: Allow access to const void pointer arguments in tracing programs selftests/bpf: Add test to access const void pointer argument in tracing program kernel/bpf/btf.c | 10 +++++++++- .../selftests/bpf/progs/verifier_btf_ctx_access.c | 9 +++++++++ 2 files changed, 18 insertions(+), 1 deletion(-)