s390/bpf: Write back tail call counter #9465
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Only BPF functions make use of the tail call counter; helpers and kfuncs ignore and most likely also clobber it. Writing it into these functions' frames is pointless and misleading, so do not do it. Fixes: dd691e8 ("s390/bpf: Implement bpf_jit_supports_subprog_tailcalls()") Signed-off-by: Ilya Leoshkevich <[email protected]>
The tailcall_bpf2bpf_hierarchy_1 test hangs on s390. Its call graph is
as follows:
entry()
subprog_tail()
bpf_tail_call_static(0) -> entry + tail_call_start
subprog_tail()
bpf_tail_call_static(0) -> entry + tail_call_start
entry() copies its tail call counter to the subprog_tail()'s frame,
which then increments it. However, the incremented result is discarded,
leading to an astronomically large number of tail calls.
Fix by writing the incremented counter back to the entry()'s frame.
Fixes: dd691e8 ("s390/bpf: Implement bpf_jit_supports_subprog_tailcalls()")
Signed-off-by: Ilya Leoshkevich <[email protected]>
The tailcall_bpf2bpf_hierarchy_fentry test hangs on s390. Its call
graph is as follows:
entry()
subprog_tail()
trampoline()
fentry()
the rest of subprog_tail() # via BPF_TRAMP_F_CALL_ORIG
return to entry()
The problem is that the rest of subprog_tail() increments the tail call
counter, but the trampoline discards the incremented value. This
results in an astronomically large number of tail calls.
Fix by making the trampoline write the incremented tail call counter
back.
Fixes: 528eb2c ("s390/bpf: Implement arch_prepare_bpf_trampoline()")
Signed-off-by: Ilya Leoshkevich <[email protected]>
…hy tests Clobbering a lot of registers and stack slots helps exposing tail call counter overwrite bugs in JITs. Signed-off-by: Ilya Leoshkevich <[email protected]>
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Pull request for series with
subject: s390/bpf: Write back tail call counter
version: 2
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=990991