[RFC bpf-next 01/11] bpf: Add iterator for spilled registers

[Joe Stringer]

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 <j...@wand.net.nz>
---
 include/linux/bpf_verifier.h | 11 +++++++++++
 kernel/bpf/verifier.c        | 16 +++++++---------
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 8f70dc181e23..a613b52ce939 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -133,6 +133,17 @@ struct bpf_verifier_state {
        u32 curframe;
 };
 
+#define __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 for_each_spilled_reg(iter, frame, reg)                         \
+       for (iter = 0, reg = __get_spilled_reg(iter, frame);            \
+            iter < frame->allocated_stack / BPF_REG_SIZE;              \
+            iter++, reg = __get_spilled_reg(iter, frame))
+
 /* linked list of verifier states used to prune search */
 struct bpf_verifier_state_list {
        struct bpf_verifier_state state;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d92d9c37affd..f40e089c3893 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2216,10 +2216,9 @@ 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)
+       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);
        }
@@ -3326,10 +3325,9 @@ 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)
+               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);
                }
@@ -3574,7 +3572,7 @@ 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;
 
@@ -3583,8 +3581,8 @@ 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)
+               for_each_spilled_reg(i, state, reg) {
+                       if (!reg)
                                continue;
                        mark_map_reg(&state->stack[i].spilled_ptr, 0, id, 
is_null);
                }
-- 
2.14.1