[PATCH bpf-next v4 01/16] bpf: Add verifier diagnostics report helpers

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Add a small diagnostics renderer for verifier reports and wire it into
the BPF build. The initial helpers emit the common text structure: a
failure header plus reusable report sections.

Wrap report prose at 100 columns so Reason and Suggestion text stays
readable without changing source or instruction gutters.

Gate the helpers on normal verifier log output from the start, so
BPF_LOG_STATS-only loads do not collect or render diagnostics.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/Makefile      |  2 +-
 kernel/bpf/diagnostics.c | 55 ++++++++++++++++++++++++++++++++++++++++
 kernel/bpf/diagnostics.h | 16 ++++++++++++
 3 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 kernel/bpf/diagnostics.c
 create mode 100644 kernel/bpf/diagnostics.h

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 4dc41bf5780c..90255d80e5be 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -6,7 +6,7 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse
 endif
 CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)
 
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o diagnostics.o
 obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o
 obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o bpf_insn_array.o
diff --git a/kernel/bpf/diagnostics.c b/kernel/bpf/diagnostics.c
new file mode 100644
index 000000000000..ba57aabd399f
--- /dev/null
+++ b/kernel/bpf/diagnostics.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (c) 2026 Meta Platforms, Inc. and affiliates.
+
+#include <linux/bpf_verifier.h>
+#include <linux/ctype.h>
+#include <linux/stdarg.h>
+
+#include "diagnostics.h"
+
+#define MEMORY_SAFETY "Memory Safety"
+#define REGISTER_TYPE_SAFETY "Register Type Safety"
+#define CALL_TYPE_SAFETY "Call Type Safety"
+#define RESOURCE_LIFETIME_SAFETY "Resource Lifetime Safety"
+#define EXECUTION_CONTEXT_SAFETY "Execution Context Safety"
+#define PROGRAM_STRUCTURE "Program Structure"
+#define POLICY "Policy"
+#define VERIFIER_LIMIT "Verifier Limit"
+
+bool bpf_diag_enabled(const struct bpf_verifier_env *env)
+{
+	return env->log.level & BPF_LOG_LEVEL;
+}
+
+static void diag_write(struct bpf_verifier_env *env, const char *fmt, ...) __printf(2, 3);
+
+static void diag_write(struct bpf_verifier_env *env, const char *fmt, ...)
+{
+	va_list args;
+
+	if (!bpf_diag_enabled(env))
+		return;
+
+	va_start(args, fmt);
+	bpf_verifier_vlog(&env->log, fmt, args);
+	va_end(args);
+}
+
+void bpf_diag_header(struct bpf_verifier_env *env, const char *category, const char *problem)
+{
+	char first;
+
+	if (!bpf_diag_enabled(env))
+		return;
+
+	category = category ?: "Verifier Error";
+	problem = problem ?: "";
+
+	if (!problem[0]) {
+		diag_write(env, "\nVerification failed: %s\n", category);
+		return;
+	}
+
+	first = toupper(problem[0]);
+	diag_write(env, "\nVerification failed: %s: %c%s\n", category, first, problem + 1);
+}
diff --git a/kernel/bpf/diagnostics.h b/kernel/bpf/diagnostics.h
new file mode 100644
index 000000000000..e8e4c06233e2
--- /dev/null
+++ b/kernel/bpf/diagnostics.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#ifndef __BPF_DIAGNOSTICS_H
+#define __BPF_DIAGNOSTICS_H
+
+#include <linux/compiler_attributes.h>
+#include <linux/types.h>
+
+struct bpf_verifier_env;
+
+bool bpf_diag_enabled(const struct bpf_verifier_env *env);
+void bpf_diag_header(struct bpf_verifier_env *env, const char *category,
+			    const char *problem);
+
+#endif /* __BPF_DIAGNOSTICS_H */
-- 
2.53.0