bpf: Add iterator for spilled registers

Add this iterator for spilled registers, it concentrates the details of
how to get the current frame's spilled registers into a single macro
while clarifying the intention of the code which is calling the macro.
Signed-off-by: Joe Stringer <joe@wand.net.nz>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/linux/bpf_verifier.h

@@ -131,6 +131,17 @@ struct bpf_verifier_state {
 	u32 curframe;
 };
 
+#define bpf_get_spilled_reg(slot, frame)				\
+	(((slot < frame->allocated_stack / BPF_REG_SIZE) &&		\
+	  (frame->stack[slot].slot_type[0] == STACK_SPILL))		\
+	 ? &frame->stack[slot].spilled_ptr : NULL)
+
+/* Iterate over 'frame', setting 'reg' to either NULL or a spilled register. */
+#define bpf_for_each_spilled_reg(iter, frame, reg)			\
+	for (iter = 0, reg = bpf_get_spilled_reg(iter, frame);		\
+	     iter < frame->allocated_stack / BPF_REG_SIZE;		\
+	     iter++, reg = bpf_get_spilled_reg(iter, frame))
+
 /* linked list of verifier states used to prune search */
 struct bpf_verifier_state_list {
 	struct bpf_verifier_state state;

kernel/bpf/verifier.c

@@ -2252,10 +2252,9 @@ static void __clear_all_pkt_pointers(struct bpf_verifier_env *env,
 		if (reg_is_pkt_pointer_any(&regs[i]))
 			mark_reg_unknown(env, regs, i);
 
-	for (i = 0; i < state->allocated_stack / BPF_REG_SIZE; i++) {
-		if (state->stack[i].slot_type[0] != STACK_SPILL)
+	bpf_for_each_spilled_reg(i, state, reg) {
+		if (!reg)
 			continue;
-		reg = &state->stack[i].spilled_ptr;
 		if (reg_is_pkt_pointer_any(reg))
 			__mark_reg_unknown(reg);
 	}
@@ -3395,10 +3394,9 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *vstate,
 
 	for (j = 0; j <= vstate->curframe; j++) {
 		state = vstate->frame[j];
-		for (i = 0; i < state->allocated_stack / BPF_REG_SIZE; i++) {
-			if (state->stack[i].slot_type[0] != STACK_SPILL)
+		bpf_for_each_spilled_reg(i, state, reg) {
+			if (!reg)
 				continue;
-			reg = &state->stack[i].spilled_ptr;
 			if (reg->type == type && reg->id == dst_reg->id)
 				reg->range = max(reg->range, new_range);
 		}
@@ -3643,7 +3641,7 @@ static void mark_map_regs(struct bpf_verifier_state *vstate, u32 regno,
 			  bool is_null)
 {
 	struct bpf_func_state *state = vstate->frame[vstate->curframe];
-	struct bpf_reg_state *regs = state->regs;
+	struct bpf_reg_state *reg, *regs = state->regs;
 	u32 id = regs[regno].id;
 	int i, j;
 
@@ -3652,8 +3650,8 @@ static void mark_map_regs(struct bpf_verifier_state *vstate, u32 regno,
 
 	for (j = 0; j <= vstate->curframe; j++) {
 		state = vstate->frame[j];
-		for (i = 0; i < state->allocated_stack / BPF_REG_SIZE; i++) {
-			if (state->stack[i].slot_type[0] != STACK_SPILL)
+		bpf_for_each_spilled_reg(i, state, reg) {
+			if (!reg)
 				continue;
 			mark_map_reg(&state->stack[i].spilled_ptr, 0, id, is_null);
 		}