s390/bpf: Write back tail call counter for BPF_PSEUDO_CALL

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[ Upstream commit c861a6b147 ]

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: dd691e847d ("s390/bpf: Implement bpf_jit_supports_subprog_tailcalls()")
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20250813121016.163375-3-iii@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

...

This commit is contained in:

Ilya Leoshkevich 2025-08-13 14:06:29 +02:00 • committed by Greg Kroah-Hartman

parent 49aba49947

commit fb66892d91

1 changed files with 16 additions and 7 deletions

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arch/s390/net/bpf_jit_comp.c

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