bpf: verifier: initialize imm in kfunc_tab in add_kfunc_call() #10259
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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 for s390 as its JIT uses this table to find the addresses for kfuncs, and if this table is not sorted properly, JIT may fail to find addresses for valid kfunc calls. This was exposed by: commit d869d56 ("bpf: verifier: refactor kfunc specialization") as before this commit, desc->imm was initialised in add_kfunc_call() which happens before dead code elimination. Move desc->imm setup down to sort_kfunc_descs_by_imm_off(), this fixes the problem and also saves us from having the same logic in add_kfunc_call() and specialize_kfunc(). Suggested-by: Eduard Zingerman <[email protected]> Signed-off-by: Puranjay Mohan <[email protected]>
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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 d869d56 ("bpf: verifier: refactor kfunc specialization")
as before this commit, desc->imm was initialised in add_kfunc_call().
Initialize desc->imm in add_kfunc_call(), it will be overwritten with new imm in specialize_kfunc() if the instruction is not removed.