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s390/bpf: Do not write tail call counter into helper and kfunc frames

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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: 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/20250813121016.163375-2-iii@linux.ibm.com
This commit is contained in:
Ilya Leoshkevich 2025-08-13 14:06:28 +02:00 committed by Daniel Borkmann
parent 3ec85602f8
commit eada40e057
1 changed files with 12 additions and 4 deletions
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16
arch/s390/net/bpf_jit_comp.c
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@ -1790,6 +1790,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
REG_SET_SEEN(BPF_REG_5);
jit->seen |= SEEN_FUNC;
/*
* Copy the tail call counter to where the callee expects it.
*
@ -1800,10 +1801,17 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
* Note 2: We assume that the verifier does not let us call the
* main program, which clears the tail call counter on entry.
*/
/* mvc tail_call_cnt(4,%r15),frame_off+tail_call_cnt(%r15) */
_EMIT6(0xd203f000 | offsetof(struct prog_frame, tail_call_cnt),
0xf000 | (jit->frame_off +
offsetof(struct prog_frame, tail_call_cnt)));
if (insn->src_reg == BPF_PSEUDO_CALL)
/*
* mvc tail_call_cnt(4,%r15),
* frame_off+tail_call_cnt(%r15)
*/
_EMIT6(0xd203f000 | offsetof(struct prog_frame,
tail_call_cnt),
0xf000 | (jit->frame_off +
offsetof(struct prog_frame,
tail_call_cnt)));
/* Sign-extend the kfunc arguments. */
if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {