From cafe2c21508a38cdb3ed22708842e957b2572c3e Mon Sep 17 00:00:00 2001
From: Eduard Zingerman <eddyz87@gmail.com>
Date: Tue, 21 Nov 2023 04:06:58 +0200
Subject: [PATCH] bpf: widening for callback iterators
Callbacks are similar to open coded iterators, so add imprecise
widening logic for callback body processing. This makes callback based
loops behave identically to open coded iterators, e.g. allowing to
verify programs like below:
struct ctx { u32 i; };
int cb(u32 idx, struct ctx* ctx)
{
++ctx->i;
return 0;
}
...
struct ctx ctx = { .i = 0 };
bpf_loop(100, cb, &ctx, 0);
...
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20231121020701.26440-9-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
kernel/bpf/verifier.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a60dfa56ebb3..2f03e6b11bb9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9799,9 +9799,10 @@ static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env)
static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
{
- struct bpf_verifier_state *state = env->cur_state;
+ struct bpf_verifier_state *state = env->cur_state, *prev_st;
struct bpf_func_state *caller, *callee;
struct bpf_reg_state *r0;
+ bool in_callback_fn;
int err;
callee = state->frame[state->curframe];
@@ -9856,7 +9857,8 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
* there function call logic would reschedule callback visit. If iteration
* converges is_state_visited() would prune that visit eventually.
*/
- if (callee->in_callback_fn)
+ in_callback_fn = callee->in_callback_fn;
+ if (in_callback_fn)
*insn_idx = callee->callsite;
else
*insn_idx = callee->callsite + 1;
@@ -9871,6 +9873,24 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
* bpf_throw, this will be done by copy_verifier_state for extra frames. */
free_func_state(callee);
state->frame[state->curframe--] = NULL;
+
+ /* for callbacks widen imprecise scalars to make programs like below verify:
+ *
+ * struct ctx { int i; }
+ * void cb(int idx, struct ctx *ctx) { ctx->i++; ... }
+ * ...
+ * struct ctx = { .i = 0; }
+ * bpf_loop(100, cb, &ctx, 0);
+ *
+ * This is similar to what is done in process_iter_next_call() for open
+ * coded iterators.
+ */
+ prev_st = in_callback_fn ? find_prev_entry(env, state, *insn_idx) : NULL;
+ if (prev_st) {
+ err = widen_imprecise_scalars(env, prev_st, state);
+ if (err)
+ return err;
+ }
return 0;
}