[PATCH bpf-next 4/7] bpf: Inline local IRQ kfunc calls during verifier fixup

[Emil Tsalapatis <emil@etsalapatis.com>]

Replace calls to the core bpf_local_irq_save() and
bpf_local_irq_restore() kfuncs with the corresponding internal IRQ
instruction when the selected JIT advertises support. Encode R1, the
flags-pointer argument register, as the instruction destination.

This runs after the original call has been checked. The existing
process_irq_flag() validation checks the stack flags operand and tracks
its initialization and IRQ-region state, so the fixup does not accept new
operand types or bypass those checks.

Keep calls unchanged for unsupported backends and configurations.

Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
---
 kernel/bpf/verifier.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 5601d2056218..aff7080b5c85 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -23372,6 +23372,16 @@ int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 			     insn->imm);
 		return -EFAULT;
 	}
+	if (!desc->offset && bpf_jit_supports_irq_save_restore() &&
+	    (desc->func_id == special_kfunc_list[KF_bpf_local_irq_save] ||
+	     desc->func_id == special_kfunc_list[KF_bpf_local_irq_restore])) {
+		int irq_op = desc->func_id == special_kfunc_list[KF_bpf_local_irq_save] ?
+			     BPF_IRQ_SAVE : BPF_IRQ_RESTORE;
+
+		insn_buf[0] = BPF_IRQ_INSN(irq_op, BPF_REG_1);
+		*cnt = 1;
+		return 0;
+	}
 	base_desc_idx = desc - env->prog->aux->kfunc_tab->descs;
 
 	near_call = !bpf_jit_supports_far_kfunc_call();
-- 
2.52.0