[PATCH bpf-next 2/2] bpf: Avoid putting struct bpf_scc_callchain variables on the stack

[Yonghong Song <yonghong.song@xxxxxxxxx>]

Add a 'struct bpf_scc_callchain callchain' field in bpf_verifier_env.
This way, the previous bpf_scc_callchain local variables can be
replaced by taking address of env->callchain. This can reduce stack
usage and fix the following error:
    kernel/bpf/verifier.c:19921:12: error: stack frame size (1368) exceeds limit (1280) in 'do_check'
        [-Werror,-Wframe-larger-than]

Reported-by: Arnd Bergmann <arnd@xxxxxxxxxx>
Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
 include/linux/bpf_verifier.h |  1 +
 kernel/bpf/verifier.c        | 36 ++++++++++++++++++------------------
 2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7e459e839f8b..e2c175d608bb 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -841,6 +841,7 @@ struct bpf_verifier_env {
 	char tmp_str_buf[TMP_STR_BUF_LEN];
 	struct bpf_insn insn_buf[INSN_BUF_SIZE];
 	struct bpf_insn epilogue_buf[INSN_BUF_SIZE];
+	struct bpf_scc_callchain callchain;
 	/* array of pointers to bpf_scc_info indexed by SCC id */
 	struct bpf_scc_info **scc_info;
 	u32 scc_cnt;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 29faef51065d..b334e6434eb4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1913,19 +1913,19 @@ static char *format_callchain(struct bpf_verifier_env *env, struct bpf_scc_callc
  */
 static int maybe_enter_scc(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
 {
-	struct bpf_scc_callchain callchain;
+	struct bpf_scc_callchain *callchain = &env->callchain;
 	struct bpf_scc_visit *visit;
 
-	if (!compute_scc_callchain(env, st, &callchain))
+	if (!compute_scc_callchain(env, st, callchain))
 		return 0;
-	visit = scc_visit_lookup(env, &callchain);
-	visit = visit ?: scc_visit_alloc(env, &callchain);
+	visit = scc_visit_lookup(env, callchain);
+	visit = visit ?: scc_visit_alloc(env, callchain);
 	if (!visit)
 		return -ENOMEM;
 	if (!visit->entry_state) {
 		visit->entry_state = st;
 		if (env->log.level & BPF_LOG_LEVEL2)
-			verbose(env, "SCC enter %s\n", format_callchain(env, &callchain));
+			verbose(env, "SCC enter %s\n", format_callchain(env, callchain));
 	}
 	return 0;
 }
@@ -1938,21 +1938,21 @@ static int propagate_backedges(struct bpf_verifier_env *env, struct bpf_scc_visi
  */
 static int maybe_exit_scc(struct bpf_verifier_env *env, struct bpf_verifier_state *st)
 {
-	struct bpf_scc_callchain callchain;
+	struct bpf_scc_callchain *callchain = &env->callchain;
 	struct bpf_scc_visit *visit;
 
-	if (!compute_scc_callchain(env, st, &callchain))
+	if (!compute_scc_callchain(env, st, callchain))
 		return 0;
-	visit = scc_visit_lookup(env, &callchain);
+	visit = scc_visit_lookup(env, callchain);
 	if (!visit) {
 		verifier_bug(env, "scc exit: no visit info for call chain %s",
-			     format_callchain(env, &callchain));
+			     format_callchain(env, callchain));
 		return -EFAULT;
 	}
 	if (visit->entry_state != st)
 		return 0;
 	if (env->log.level & BPF_LOG_LEVEL2)
-		verbose(env, "SCC exit %s\n", format_callchain(env, &callchain));
+		verbose(env, "SCC exit %s\n", format_callchain(env, callchain));
 	visit->entry_state = NULL;
 	env->num_backedges -= visit->num_backedges;
 	visit->num_backedges = 0;
@@ -1967,22 +1967,22 @@ static int add_scc_backedge(struct bpf_verifier_env *env,
 			    struct bpf_verifier_state *st,
 			    struct bpf_scc_backedge *backedge)
 {
-	struct bpf_scc_callchain callchain;
+	struct bpf_scc_callchain *callchain = &env->callchain;
 	struct bpf_scc_visit *visit;
 
-	if (!compute_scc_callchain(env, st, &callchain)) {
+	if (!compute_scc_callchain(env, st, callchain)) {
 		verifier_bug(env, "add backedge: no SCC in verification path, insn_idx %d",
 			     st->insn_idx);
 		return -EFAULT;
 	}
-	visit = scc_visit_lookup(env, &callchain);
+	visit = scc_visit_lookup(env, callchain);
 	if (!visit) {
 		verifier_bug(env, "add backedge: no visit info for call chain %s",
-			     format_callchain(env, &callchain));
+			     format_callchain(env, callchain));
 		return -EFAULT;
 	}
 	if (env->log.level & BPF_LOG_LEVEL2)
-		verbose(env, "SCC backedge %s\n", format_callchain(env, &callchain));
+		verbose(env, "SCC backedge %s\n", format_callchain(env, callchain));
 	backedge->next = visit->backedges;
 	visit->backedges = backedge;
 	visit->num_backedges++;
@@ -1998,12 +1998,12 @@ static int add_scc_backedge(struct bpf_verifier_env *env,
 static bool incomplete_read_marks(struct bpf_verifier_env *env,
 				  struct bpf_verifier_state *st)
 {
-	struct bpf_scc_callchain callchain;
+	struct bpf_scc_callchain *callchain = &env->callchain;
 	struct bpf_scc_visit *visit;
 
-	if (!compute_scc_callchain(env, st, &callchain))
+	if (!compute_scc_callchain(env, st, callchain))
 		return false;
-	visit = scc_visit_lookup(env, &callchain);
+	visit = scc_visit_lookup(env, callchain);
 	if (!visit)
 		return false;
 	return !!visit->backedges;
-- 
2.47.1