[PATCH bpf-next v1 6/8] bpf: Add verifier support for custom callback return range

[Joanne Koong <joannelkoong@gmail.com>]

This is ported from Dave Marchevsky's patch [0], which is needed for the
bpf iterators callback to return values beyond the 0, 1 range.

For comments, please refer to Dave's patch.

[0] https://lore.kernel.org/bpf/20220830172759.4069786-2-davemarchevsky@fb.com/

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
---
 include/linux/bpf_verifier.h | 1 +
 kernel/bpf/verifier.c        | 5 +++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 8fbc1d05281e..63cda732ee10 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -248,6 +248,7 @@ struct bpf_func_state {
 	 */
 	u32 async_entry_cnt;
 	bool in_callback_fn;
+	struct tnum callback_ret_range;
 	bool in_async_callback_fn;
 
 	/* The following fields should be last. See copy_func_state() */
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 8c8c101513f5..2eb2a4410344 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1814,6 +1814,7 @@ static void init_func_state(struct bpf_verifier_env *env,
 	state->callsite = callsite;
 	state->frameno = frameno;
 	state->subprogno = subprogno;
+	state->callback_ret_range = tnum_range(0, 1);
 	init_reg_state(env, state);
 	mark_verifier_state_scratched(env);
 }
@@ -6974,6 +6975,7 @@ static int set_find_vma_callback_state(struct bpf_verifier_env *env,
 	__mark_reg_not_init(env, &callee->regs[BPF_REG_4]);
 	__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
 	callee->in_callback_fn = true;
+	callee->callback_ret_range = tnum_range(0, 1);
 	return 0;
 }
 
@@ -7000,8 +7002,7 @@ static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
 	state->curframe--;
 	caller = state->frame[state->curframe];
 	if (callee->in_callback_fn) {
-		/* enforce R0 return value range [0, 1]. */
-		struct tnum range = tnum_range(0, 1);
+		struct tnum range = callee->callback_ret_range;
 
 		if (r0->type != SCALAR_VALUE) {
 			verbose(env, "R0 not a scalar value\n");
-- 
2.30.2