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[v2,bpf-next,02/10] bpf: enforce precision of R0 on callback return

Message ID 20231129003620.1049610-3-andrii@kernel.org (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series BPF verifier retval logic fixes | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for bpf-next
netdev/apply fail Patch does not apply to bpf-next
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Commit Message

Andrii Nakryiko Nov. 29, 2023, 12:36 a.m. UTC 
Given verifier checks actual value, r0 has to be precise, so we need to
propagate precision properly. r0 also has to be marked as read,
otherwise subsequent state comparisons will ignore such register as
unimportant and precision won't really help here.

Fixes: 69c087ba6225 ("bpf: Add bpf_for_each_map_elem() helper")
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/bpf/verifier.c | 7 +++++++
 1 file changed, 7 insertions(+)
diff mbox series

Patch

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 25b9d470957e..849fbf47b5f3 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9590,6 +9590,13 @@  static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 			verbose(env, "R0 not a scalar value\n");
 			return -EACCES;
 		}
+
+		/* we are going to rely on register's precise value */
+		err = mark_reg_read(env, r0, r0->parent, REG_LIVE_READ64);
+		err = err ?: mark_chain_precision(env, BPF_REG_0);
+		if (err)
+			return err;
+
 		if (!tnum_in(range, r0->var_off)) {
 			verbose_invalid_scalar(env, r0, &range, "callback return", "R0");
 			return -EINVAL;