On Mar 24 2024, Alexei Starovoitov wrote:
On Sat, Mar 23, 2024 at 9:57 PM Kumar Kartikeya Dwivedi memxor@gmail.com wrote:
Observation is correct. The patch is buggy, but the suggestion to follow process_dynptr_func() will lead to unnecessary complexity. dynptr-s are on stack with plenty of extra checks.
The suggestion was to call process_timer_func, not process_dynptr_func.
In this case bpf_timer is in map_value. Much simpler is to follow KF_ARG_PTR_TO_MAP approach.
What I meant by the example was that dynptr handling does the same thing for kfuncs and helpers (using the same function), so timer arguments should do the same (i.e. use process_timer_func), which will do all checks for constant offset (ensuring var_off is tnum_is_const) and match it against btf_record->timer_off.
I don't follow. Please elaborate with a patch. The var_off and off is a part of the bug, but it's not the biggest part of it.
Not compile tested.
Compiles just fine :)
I see. All makes sense to me.
Benjamin, pls incorporate it in your set.
OK, done!
I just had to revert to the following or KF_ARG_TIMER_ID was not recognized by the verifier:
--- diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7ee20e9d14bd..a5e147468ac8 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -10848,7 +10848,7 @@ BTF_ID(struct, bpf_list_head) BTF_ID(struct, bpf_list_node) BTF_ID(struct, bpf_rb_root) BTF_ID(struct, bpf_rb_node) -BTF_ID(struct, bpf_timer) +BTF_ID(struct, bpf_timer_kern)
static bool __is_kfunc_ptr_arg_type(const struct btf *btf, const struct btf_param *arg, int type) ---
Cheers, Benjamin