Merge branch 'bpf-allow-bpf_for_each_map_elem-helper-with-different-input-maps'

Philo Lu says:

====================
bpf: allow bpf_for_each_map_elem() helper with different input maps

Currently, taking different maps within a single bpf_for_each_map_elem
call is not allowed. For example the following codes cannot pass the
verifier (with error "tail_call abusing map_ptr"):
```
static void test_by_pid(int pid)
{
	if (pid <= 100)
		bpf_for_each_map_elem(&map1, map_elem_cb, NULL, 0);
	else
		bpf_for_each_map_elem(&map2, map_elem_cb, NULL, 0);
}
```

This is because during bpf_for_each_map_elem verifying,
bpf_insn_aux_data->map_ptr_state is expected as map_ptr (instead of poison
state), which is then needed by set_map_elem_callback_state. However, as
there are two different map ptr input, map_ptr_state is marked as
BPF_MAP_PTR_POISON, and thus the second map_ptr would be lost.
BPF_MAP_PTR_POISON is also needed by bpf_for_each_map_elem to skip
retpoline optimization in do_misc_fixups(). Therefore, map_ptr_state and
map_ptr are both needed for bpf_for_each_map_elem.

This patchset solves it by transform bpf_insn_aux_data->map_ptr_state as a
new struct, storing poison/unpriv state and map pointer together without
additional memory overhead. Then bpf_for_each_map_elem works well with
different input maps. It also makes map_ptr_state logic clearer.

A test case is added to selftest, which would fail to load without this
patchset.

Changelogs
-> v1:
- PATCH 1/3:
  - make the commit log clearer
  - change poison and unpriv to bool in struct bpf_map_ptr_state, also the
    return value in bpf_map_ptr_poisoned() and bpf_map_ptr_unpriv()
- PATCH 2/3:
  - change the comments in set_map_elem_callback_state()
- PATCH 3/3:
  - remove the "skipping the last element" logic during map updating
  - change if() to ASSERT_OK()

Please review, thanks.
====================

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

1 files changed, 8 insertions, 1 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7cb1b75eee38..36d19cd32eb5 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -502,6 +502,13 @@ struct bpf_loop_inline_state {
 	u32 callback_subprogno; /* valid when fit_for_inline is true */
 };
 
+/* pointer and state for maps */
+struct bpf_map_ptr_state {
+	struct bpf_map *map_ptr;
+	bool poison;
+	bool unpriv;
+};
+
 /* Possible states for alu_state member. */
 #define BPF_ALU_SANITIZE_SRC		(1U << 0)
 #define BPF_ALU_SANITIZE_DST		(1U << 1)
@@ -514,7 +521,7 @@ struct bpf_loop_inline_state {
 struct bpf_insn_aux_data {
 	union {
 		enum bpf_reg_type ptr_type;	/* pointer type for load/store insns */
-		unsigned long map_ptr_state;	/* pointer/poison value for maps */
+		struct bpf_map_ptr_state map_ptr_state;
 		s32 call_imm;			/* saved imm field of call insn */
 		u32 alu_limit;			/* limit for add/sub register with pointer */
 		struct {