Filtering pid_tgid is meaningless when the current task is preempted by
an interrupt.
To address this, introduce the bpf_in_interrupt kfunc, which allows BPF
programs to determine whether they are executing in interrupt context.
This enables programs to avoid applying pid_tgid filtering when running
in such contexts.
Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>
---
kernel/bpf/helpers.c | 9 +++++++++
kernel/bpf/verifier.c | 11 +++++++++++
2 files changed, 20 insertions(+)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index cdffd74ddbe65..21e14697804e5 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3714,6 +3714,14 @@ __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)
@@ -3754,6 +3762,7 @@ 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 = {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4e47992361ea1..365d42140941d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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)
@@ -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)
{
@@ -21973,6 +21975,15 @@ 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]) {
+#ifdef CONFIG_X86_64
+ 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) {
--
2.50.1
