Metadata about a kfunc call is added to the kfunc_tab in add_kfunc_call() but the call instruction itself could get removed by opt_remove_dead_code() later if it is not reachable. If the call instruction is removed, specialize_kfunc() is never called for it and the desc->imm in the kfunc_tab is never initialized for this kfunc call. In this case, sort_kfunc_descs_by_imm_off(env->prog); in do_misc_fixups() doesn't sort the table correctly. This is a problem from s390 as its JIT uses this table to find the addresses for kfuncs, and if this table is not sorted properly, JIT can fail to find addresses for valid kfunc calls. This was exposed by: commit d869d56ca848 ("bpf: verifier: refactor kfunc specialization") as before this commit, desc->imm was initialised in add_kfunc_call(). Initialize desc->imm to func_id, it will be overwritten in specialize_kfunc() if the instruction is not removed. Fixes: d869d56ca848 ("bpf: verifier: refactor kfunc specialization") Signed-off-by: Puranjay Mohan --- This bug is not triggered by the CI currently, I am working on another set for non-sleepbale arena allocations and as part of that I am adding a new selftest that triggers this bug. Selftest: https://github.com/kernel-patches/bpf/pull/10242/commits/1f681f022c6d685fd76695e5eafbe9d9ab4c0002 CI run: https://github.com/kernel-patches/bpf/actions/runs/19238699806/job/54996376908 --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1268fa075d4c..a667f761173c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3371,6 +3371,7 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset) desc = &tab->descs[tab->nr_descs++]; desc->func_id = func_id; + desc->imm = func_id; desc->offset = offset; desc->addr = addr; desc->func_model = func_model; -- 2.47.3