An update for verifier.c:states_equal()/regsafe() to use check_ids() for active spin lock comparisons. This fixes the issue reported by Kumar Kartikeya Dwivedi in [1] using technique suggested by Edward Cree. W/o this commit the verifier might be tricked to accept the following program working with a map containing spin locks: 0: r9 = map_lookup_elem(...) ; Returns PTR_TO_MAP_VALUE_OR_NULL id=1. 1: r8 = map_lookup_elem(...) ; Returns PTR_TO_MAP_VALUE_OR_NULL id=2. 2: if r9 == 0 goto exit ; r9 -> PTR_TO_MAP_VALUE. 3: if r8 == 0 goto exit ; r8 -> PTR_TO_MAP_VALUE. 4: r7 = ktime_get_ns() ; Unbound SCALAR_VALUE. 5: r6 = ktime_get_ns() ; Unbound SCALAR_VALUE. 6: bpf_spin_lock(r8) ; active_lock.id == 2. 7: if r6 > r7 goto +1 ; No new information about the state ; is derived from this check, thus ; produced verifier states differ only ; in 'insn_idx'. 8: r9 = r8 ; Optionally make r9.id == r8.id. --- checkpoint --- ; Assume is_state_visisted() creates a ; checkpoint here. 9: bpf_spin_unlock(r9) ; (a,b) active_lock.id == 2. ; (a) r9.id == 2, (b) r9.id == 1. 10: exit(0) Consider two verification paths: (a) 0-10 (b) 0-7,9-10 The path (a) is verified first. If checkpoint is created at (8) the (b) would assume that (8) is safe because regsafe() does not compare register ids for registers of type PTR_TO_MAP_VALUE. [1] https://lore.kernel.org/bpf/20221111202719.982118-1-memxor@gmail.com/
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| @@ -13119,7 +13119,8 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold, · 13118 unmodified lines | |||
| 13119 | */ | 13119 | */ |
| 13120 | return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) == 0 && | 13120 | return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) == 0 && |
| 13121 | range_within(rold, rcur) && | 13121 | range_within(rold, rcur) && |
| 13122 | tnum_in(rold->var_off, rcur->var_off); | 13122 | tnum_in(rold->var_off, rcur->var_off) && |
| 13123 | check_ids(rold->id, rcur->id, idmap); | ||
| 13123 | case PTR_TO_PACKET_META: | 13124 | case PTR_TO_PACKET_META: |
| 13124 | case PTR_TO_PACKET: | 13125 | case PTR_TO_PACKET: |
| 13125 | if (rcur->type != rold->type) | 13126 | if (rcur->type != rold->type) |
| @@ -13291,8 +13292,17 @@ static bool states_equal(struct bpf_verifier_env *env, · 165 unmodified lines | |||
| 13291 | if (old->speculative && !cur->speculative) | 13292 | if (old->speculative && !cur->speculative) |
| 13292 | return false; | 13293 | return false; |
| 13293 | 13294 | ||
| 13294 | if (old->active_lock.ptr != cur->active_lock.ptr || | 13295 | if (old->active_lock.ptr != cur->active_lock.ptr) |
| 13295 | old->active_lock.id != cur->active_lock.id) | 13296 | return false; |
| 13297 | |||
| 13298 | /* Old and cur active_lock's have to be either both present | ||
| 13299 | * or both absent. | ||
| 13300 | */ | ||
| 13301 | if (!!old->active_lock.id != !!cur->active_lock.id) | ||
| 13302 | return false; | ||
| 13303 | |||
| 13304 | if (old->active_lock.id && | ||
| 13305 | !check_ids(old->active_lock.id, cur->active_lock.id, env->idmap_scratch)) | ||
| 13296 | return false; | 13306 | return false; |
| 13297 | 13307 | ||
| 13298 | if (old->active_rcu_lock != cur->active_rcu_lock) | 13308 | if (old->active_rcu_lock != cur->active_rcu_lock) |