bpf: Update env->prev_insn_idx after do_check_insn() #9221
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To introduce prev_aux(env), env->prev_insn_idx must be up-to-date directly after do_check_insn(). To achieve this, replace prev_insn_idx with a tmp variable (to discourage use) and update env->prev_insn_idx directly after do_check_insn(). A concern would be that some code relied on env->prev_insn_idx still having the old value between do_check_insn() and the old update-assignment. However, outside the do_check() function it is only used through push_jmp_history()/do_check_insn()/is_state_visisted() which are not called in-between the old and new assignment location. This can also be seen from the -O0 call graph for push_jmp_history() [1]. [1] https://sys.cs.fau.de/extern/person/gerhorst/25-06_d69baf_push_jmp_history_O0_callgraph.png Signed-off-by: Luis Gerhorst <[email protected]>
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To introduce prev_aux(env), env->prev_insn_idx must be up-to-date directly after do_check_insn(). To achieve this, replace prev_insn_idx with a tmp variable (to discourage use) and update env->prev_insn_idx directly after do_check_insn().
A concern would be that some code relied on env->prev_insn_idx still having the old value between do_check_insn() and the old update-assignment. However, outside the do_check() function it is only used through push_jmp_history()/do_check_insn()/is_state_visisted() which are not called in-between the old and new assignment location. This can also be seen from the -O0 call graph for push_jmp_history() [1].
[1] https://sys.cs.fau.de/extern/person/gerhorst/25-06_d69baf_push_jmp_history_O0_callgraph.png