From 1a5a03617bb997999356680b45faf5dd9c9a2e72 Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Tue, 21 Nov 2023 04:06:58 +0200 Subject: [PATCH] bpf: widening for callback iterators commit cafe2c21508a38cdb3ed22708842e957b2572c3e upstream. 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 Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20231121020701.26440-9-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Greg Kroah-Hartman --- 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 78ae9cf..c934d27 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9595,9 +9595,10 @@ 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]; @@ -9659,7 +9660,8 @@ 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; @@ -9673,6 +9675,24 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx) /* clear everything in the callee */ 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; } -- 2.7.4