The trampoline could be corrupted by the blindly 'tr->flags = BPF_TRAMP_F_TAIL_CALL_CTX' in verifier.
1. A fexit attached to a tail_call_reachable prog. 'tr->flags' became 'BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_TAIL_CALL_CTX'. And, the trampoline would poke the target prog's nop insn using jmp insn instead of call insn. 2. Another fexit loaded with the same tail_call_reachable prog target. 'tr->flags' became 'BPF_TRAMP_F_TAIL_CALL_CTX'. 3. Close the first fexit link. Due to no BPF_TRAMP_F_CALL_ORIG in 'tr->flags', the trampoline will fail to restore the prog's nop insn using call insn. [ 3.410719] WARNING: kernel/bpf/syscall.c:3551 at bpf_tracing_link_release+0x53/0x60, CPU#1: test_progs/98 ... [ 3.428793] bpf_link_free+0x58/0x130 [ 3.429293] bpf_link_release+0x23/0x30 Fix the warning by updating 'tr->flags' with '|=' and lock. Changes: v1 -> v2: * Update the patch #1 message with 'tr->flags' change. (per Jiri) * Drop the 'link' and the last 'if' in patch #2. (per Jiri) * v1: https://lore.kernel.org/bpf/[email protected]/ Leon Hwang (2): bpf: Fix WARNING in bpf_tracing_link_release selftests/bpf: Verify no warning when close fexit link include/linux/bpf.h | 2 + kernel/bpf/trampoline.c | 7 +++ kernel/bpf/verifier.c | 2 +- .../selftests/bpf/prog_tests/tailcalls.c | 48 +++++++++++++++++++ 4 files changed, 58 insertions(+), 1 deletion(-) -- 2.55.0
