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bpf: Introduce bpf_in_interrupt kfunc #5811

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37d3724
bpf: Introduce bpf_in_interrupt kfunc
Asphaltt Aug 25, 2025
746416f
selftests/bpf: Add case to test bpf_in_interrupt kfunc
Asphaltt Aug 25, 2025
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9 changes: 9 additions & 0 deletions kernel/bpf/helpers.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3711,6 +3711,14 @@ __bpf_kfunc int bpf_strstr(const char *s1__ign, const char *s2__ign)
return bpf_strnstr(s1__ign, s2__ign, XATTR_SIZE_MAX);
}

/**
* bpf_in_interrupt - Check whether it's in interrupt context
*/
__bpf_kfunc int bpf_in_interrupt(void)
{
return in_interrupt();
}

__bpf_kfunc_end_defs();

BTF_KFUNCS_START(generic_btf_ids)
Expand Down Expand Up @@ -3751,6 +3759,7 @@ BTF_ID_FLAGS(func, bpf_throw)
#ifdef CONFIG_BPF_EVENTS
BTF_ID_FLAGS(func, bpf_send_signal_task, KF_TRUSTED_ARGS)
#endif
BTF_ID_FLAGS(func, bpf_in_interrupt, KF_FASTCALL)
BTF_KFUNCS_END(generic_btf_ids)

static const struct btf_kfunc_id_set generic_kfunc_set = {
Expand Down
11 changes: 11 additions & 0 deletions kernel/bpf/verifier.c
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Original file line number Diff line number Diff line change
Expand Up @@ -12259,6 +12259,7 @@ enum special_kfunc_type {
KF_bpf_res_spin_lock_irqsave,
KF_bpf_res_spin_unlock_irqrestore,
KF___bpf_trap,
KF_bpf_in_interrupt,
};

BTF_ID_LIST(special_kfunc_list)
Expand Down Expand Up @@ -12327,6 +12328,7 @@ BTF_ID(func, bpf_res_spin_unlock)
BTF_ID(func, bpf_res_spin_lock_irqsave)
BTF_ID(func, bpf_res_spin_unlock_irqrestore)
BTF_ID(func, __bpf_trap)
BTF_ID(func, bpf_in_interrupt)

static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
{
Expand Down Expand Up @@ -21977,6 +21979,15 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
desc->func_id == special_kfunc_list[KF_bpf_rdonly_cast]) {
insn_buf[0] = BPF_MOV64_REG(BPF_REG_0, BPF_REG_1);
*cnt = 1;
} else if (desc->func_id == special_kfunc_list[KF_bpf_in_interrupt]) {
#if defined(CONFIG_X86_64) && !defined(CONFIG_UML)
insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, (u32)(unsigned long)&__preempt_count);
insn_buf[1] = BPF_MOV64_PERCPU_REG(BPF_REG_0, BPF_REG_0);
insn_buf[2] = BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_0, 0);
insn_buf[3] = BPF_ALU32_IMM(BPF_AND, BPF_REG_0, NMI_MASK | HARDIRQ_MASK |
(IS_ENABLED(CONFIG_PREEMPT_RT) ? 0 : SOFTIRQ_MASK));
*cnt = 4;
#endif
}

if (env->insn_aux_data[insn_idx].arg_prog) {
Expand Down
7 changes: 7 additions & 0 deletions tools/testing/selftests/bpf/progs/irq.c
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Expand Up @@ -563,4 +563,11 @@ int irq_wrong_kfunc_class_2(struct __sk_buff *ctx)
return 0;
}

SEC("?tc")
__success
int in_interrupt(struct __sk_buff *ctx)
{
return bpf_in_interrupt();
}

char _license[] SEC("license") = "GPL";
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