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Add a selftest to verify that the verifier correctly identifies refcounted arguments in struct_ops programs, even when they are not the first argument. This ensures that the restriction on tail calls for programs with __ref arguments is properly enforced regardless of which argument they appear in. This test verifies the fix for check_struct_ops_btf_id() proposed by Keisuke Nishimura [0], which corrected a bug where only the first argument was checked for the refcounted flag. The test includes: - An update to bpf_testmod to add 'test_refcounted_multi', an operator with three arguments where the third is tagged with "__ref". - A BPF program 'test_refcounted_multi' that attempts a tail call. - A test runner that asserts the verifier rejects the program with "program with __ref argument cannot tail call". [0]: https://lore.kernel.org/bpf/20260320130219.63711-1-keisuke.nishimura@inria.fr/ Signed-off-by: Varun R Mallya <varunrmallya@gmail.com> Link: https://lore.kernel.org/r/20260321214038.80479-1-varunrmallya@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
36 lines
953 B
C
36 lines
953 B
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2026 Varun R Mallya */
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#include <vmlinux.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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#include "../test_kmods/bpf_testmod.h"
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#include "bpf_misc.h"
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char _license[] SEC("license") = "GPL";
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struct {
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__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
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__uint(max_entries, 1);
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__uint(key_size, sizeof(__u32));
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__uint(value_size, sizeof(__u32));
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} prog_array SEC(".maps");
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SEC("struct_ops/test_refcounted_multi")
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__failure __msg("program with __ref argument cannot tail call")
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int test_refcounted_multi(unsigned long long *ctx)
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{
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/* ctx[2] is used because the refcounted variable is the third argument */
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struct task_struct *refcounted_task = (struct task_struct *)ctx[2];
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bpf_task_release(refcounted_task);
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bpf_tail_call(ctx, &prog_array, 0);
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return 0;
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}
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SEC(".struct_ops.link")
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struct bpf_testmod_ops testmod_ref_acquire = {
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.test_refcounted_multi = (void *)test_refcounted_multi,
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};
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