In mark_chain_precision() logic, when we reach the entry to a global
func, it is expected that R1-R5 might be still requested to be marked
precise. This would correspond to some integer input arguments being
tracked as precise. This is all expected and handled as a special case.
What's not expected is that we'll leave backtrack_state structure with
some register bits set. This is because for subsequent precision
propagations backtrack_state is reused without clearing masks, as all
code paths are carefully written in a way to leave empty backtrack_state
with zeroed out masks, for speed.
The fix is trivial, we always clear register bit in the register mask, and
then, optionally, set reg->precise if register is SCALAR_VALUE type.
Reported-by: Chris Mason <clm@xxxxxxxx>
Fixes: be2ef8161572 ("bpf: allow precision tracking for programs with subprogs")
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
kernel/bpf/verifier.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index bb78212fa5b2..c0c7d137066a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4047,11 +4047,9 @@ static int __mark_chain_precision(struct bpf_verifier_env *env, int regno)
bitmap_from_u64(mask, bt_reg_mask(bt));
for_each_set_bit(i, mask, 32) {
reg = &st->frame[0]->regs[i];
- if (reg->type != SCALAR_VALUE) {
- bt_clear_reg(bt, i);
- continue;
- }
- reg->precise = true;
+ bt_clear_reg(bt, i);
+ if (reg->type == SCALAR_VALUE)
+ reg->precise = true;
}
return 0;
}
--
2.34.1
