bpf: Move backtracking logic to backtrack.c

Move precision propagation and backtracking logic to backtrack.c
to reduce verifier.c size.

No functional changes.

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20260412152936.54262-6-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf_verifier.h

@@ -279,6 +279,8 @@ static inline void spis_or_range(spis_t *mask, u32 lo, u32 hi)
 			  (1 << BPF_REG_3) | (1 << BPF_REG_4) | \
 			  (1 << BPF_REG_5))
 
+#define BPF_MAIN_FUNC (-1)
+
 #define BPF_DYNPTR_SIZE		sizeof(struct bpf_dynptr_kern)
 #define BPF_DYNPTR_NR_SLOTS		(BPF_DYNPTR_SIZE / BPF_REG_SIZE)
 
@@ -1079,6 +1081,7 @@ void bpf_free_verifier_state(struct bpf_verifier_state *state, bool free_self);
 void bpf_free_backedges(struct bpf_scc_visit *visit);
 int bpf_push_jmp_history(struct bpf_verifier_env *env, struct bpf_verifier_state *cur,
 			 int insn_flags, u64 linked_regs);
+void bpf_bt_sync_linked_regs(struct backtrack_state *bt, struct bpf_jmp_history_entry *hist);
 void bpf_mark_reg_not_init(const struct bpf_verifier_env *env,
 			   struct bpf_reg_state *reg);
 void bpf_mark_reg_unknown_imprecise(struct bpf_reg_state *reg);
@@ -1120,6 +1123,11 @@ static inline bool bpf_is_spilled_reg(const struct bpf_stack_state *stack)
 	return stack->slot_type[BPF_REG_SIZE - 1] == STACK_SPILL;
 }
 
+static inline bool bpf_is_spilled_scalar_reg(const struct bpf_stack_state *stack)
+{
+	return bpf_is_spilled_reg(stack) && stack->spilled_ptr.type == SCALAR_VALUE;
+}
+
 static inline bool bpf_register_is_null(struct bpf_reg_state *reg)
 {
 	return reg->type == SCALAR_VALUE && tnum_equals_const(reg->var_off, 0);
@@ -1135,6 +1143,16 @@ static inline void bpf_bt_set_frame_slot(struct backtrack_state *bt, u32 frame,
 	bt->stack_masks[frame] |= 1ull << slot;
 }
 
+static inline bool bt_is_frame_reg_set(struct backtrack_state *bt, u32 frame, u32 reg)
+{
+	return bt->reg_masks[frame] & (1 << reg);
+}
+
+static inline bool bt_is_frame_slot_set(struct backtrack_state *bt, u32 frame, u32 slot)
+{
+	return bt->stack_masks[frame] & (1ull << slot);
+}
+
 bool bpf_map_is_rdonly(const struct bpf_map *map);
 int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val,
 			bool is_ldsx);

kernel/bpf/Makefile

@@ -11,7 +11,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o
 obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o bpf_insn_array.o
 obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
-obj-$(CONFIG_BPF_SYSCALL) += fixups.o cfg.o states.o
+obj-$(CONFIG_BPF_SYSCALL) += fixups.o cfg.o states.o backtrack.o
 obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o mprog.o
 obj-$(CONFIG_BPF_JIT) += trampoline.o