[RFC PATCH 05/30] lib: code tagging framework

[Suren Baghdasaryan <surenb@xxxxxxxxxx>]

Add basic infrastructure to support code tagging which stores tag common
information consisting of the module name, function, file name and line
number. Provide functions to register a new code tag type and navigate
between code tags.

Co-developed-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
 include/linux/codetag.h |  71 ++++++++++++++
 lib/Kconfig.debug       |   4 +
 lib/Makefile            |   1 +
 lib/codetag.c           | 199 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 275 insertions(+)
 create mode 100644 include/linux/codetag.h
 create mode 100644 lib/codetag.c

diff --git a/include/linux/codetag.h b/include/linux/codetag.h
new file mode 100644
index 000000000000..a9d7adecc2a5
--- /dev/null
+++ b/include/linux/codetag.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * code tagging framework
+ */
+#ifndef _LINUX_CODETAG_H
+#define _LINUX_CODETAG_H
+
+#include <linux/types.h>
+
+struct codetag_iterator;
+struct codetag_type;
+struct seq_buf;
+struct module;
+
+/*
+ * An instance of this structure is created in a special ELF section at every
+ * code location being tagged.  At runtime, the special section is treated as
+ * an array of these.
+ */
+struct codetag {
+       unsigned int flags; /* used in later patches */
+       unsigned int lineno;
+       const char *modname;
+       const char *function;
+       const char *filename;
+} __aligned(8);
+
+union codetag_ref {
+       struct codetag *ct;
+};
+
+struct codetag_range {
+       struct codetag *start;
+       struct codetag *stop;
+};
+
+struct codetag_module {
+       struct module *mod;
+       struct codetag_range range;
+};
+
+struct codetag_type_desc {
+       const char *section;
+       size_t tag_size;
+};
+
+struct codetag_iterator {
+       struct codetag_type *cttype;
+       struct codetag_module *cmod;
+       unsigned long mod_id;
+       struct codetag *ct;
+};
+
+#define CODE_TAG_INIT {                                        \
+       .modname        = KBUILD_MODNAME,               \
+       .function       = __func__,                     \
+       .filename       = __FILE__,                     \
+       .lineno         = __LINE__,                     \
+       .flags          = 0,                            \
+}
+
+void codetag_lock_module_list(struct codetag_type *cttype, bool lock);
+struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype);
+struct codetag *codetag_next_ct(struct codetag_iterator *iter);
+
+void codetag_to_text(struct seq_buf *out, struct codetag *ct);
+
+struct codetag_type *
+codetag_register_type(const struct codetag_type_desc *desc);
+
+#endif /* _LINUX_CODETAG_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index bcbe60d6c80c..22bc1eff7f8f 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -969,6 +969,10 @@ config DEBUG_STACKOVERFLOW
 
          If in doubt, say "N".
 
+config CODE_TAGGING
+       bool
+       select KALLSYMS
+
 source "lib/Kconfig.kasan"
 source "lib/Kconfig.kfence"
 
diff --git a/lib/Makefile b/lib/Makefile
index cc7762748708..574d7716e640 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -227,6 +227,7 @@ obj-$(CONFIG_OF_RECONFIG_NOTIFIER_ERROR_INJECT) += \
        of-reconfig-notifier-error-inject.o
 obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
 
+obj-$(CONFIG_CODE_TAGGING) += codetag.o
 lib-$(CONFIG_GENERIC_BUG) += bug.o
 
 obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
diff --git a/lib/codetag.c b/lib/codetag.c
new file mode 100644
index 000000000000..7708f8388e55
--- /dev/null
+++ b/lib/codetag.c
@@ -0,0 +1,199 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/codetag.h>
+#include <linux/idr.h>
+#include <linux/kallsyms.h>
+#include <linux/module.h>
+#include <linux/seq_buf.h>
+#include <linux/slab.h>
+
+struct codetag_type {
+       struct list_head link;
+       unsigned int count;
+       struct idr mod_idr;
+       struct rw_semaphore mod_lock; /* protects mod_idr */
+       struct codetag_type_desc desc;
+};
+
+static DEFINE_MUTEX(codetag_lock);
+static LIST_HEAD(codetag_types);
+
+void codetag_lock_module_list(struct codetag_type *cttype, bool lock)
+{
+       if (lock)
+               down_read(&cttype->mod_lock);
+       else
+               up_read(&cttype->mod_lock);
+}
+
+struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype)
+{
+       struct codetag_iterator iter = {
+               .cttype = cttype,
+               .cmod = NULL,
+               .mod_id = 0,
+               .ct = NULL,
+       };
+
+       return iter;
+}
+
+static inline struct codetag *get_first_module_ct(struct codetag_module *cmod)
+{
+       return cmod->range.start < cmod->range.stop ? cmod->range.start : NULL;
+}
+
+static inline
+struct codetag *get_next_module_ct(struct codetag_iterator *iter)
+{
+       struct codetag *res = (struct codetag *)
+                       ((char *)iter->ct + iter->cttype->desc.tag_size);
+
+       return res < iter->cmod->range.stop ? res : NULL;
+}
+
+struct codetag *codetag_next_ct(struct codetag_iterator *iter)
+{
+       struct codetag_type *cttype = iter->cttype;
+       struct codetag_module *cmod;
+       struct codetag *ct;
+
+       lockdep_assert_held(&cttype->mod_lock);
+
+       if (unlikely(idr_is_empty(&cttype->mod_idr)))
+               return NULL;
+
+       ct = NULL;
+       while (true) {
+               cmod = idr_find(&cttype->mod_idr, iter->mod_id);
+
+               /* If module was removed move to the next one */
+               if (!cmod)
+                       cmod = idr_get_next_ul(&cttype->mod_idr,
+                                              &iter->mod_id);
+
+               /* Exit if no more modules */
+               if (!cmod)
+                       break;
+
+               if (cmod != iter->cmod) {
+                       iter->cmod = cmod;
+                       ct = get_first_module_ct(cmod);
+               } else
+                       ct = get_next_module_ct(iter);
+
+               if (ct)
+                       break;
+
+               iter->mod_id++;
+       }
+
+       iter->ct = ct;
+       return ct;
+}
+
+void codetag_to_text(struct seq_buf *out, struct codetag *ct)
+{
+       seq_buf_printf(out, "%s:%u module:%s func:%s",
+                      ct->filename, ct->lineno,
+                      ct->modname, ct->function);
+}
+
+static inline size_t range_size(const struct codetag_type *cttype,
+                               const struct codetag_range *range)
+{
+       return ((char *)range->stop - (char *)range->start) /
+                       cttype->desc.tag_size;
+}
+
+static void *get_symbol(struct module *mod, const char *prefix, const char 
*name)
+{
+       char buf[64];
+       int res;
+
+       res = snprintf(buf, sizeof(buf), "%s%s", prefix, name);
+       if (WARN_ON(res < 1 || res > sizeof(buf)))
+               return NULL;
+
+       return mod ?
+               (void *)find_kallsyms_symbol_value(mod, buf) :
+               (void *)kallsyms_lookup_name(buf);
+}
+
+static struct codetag_range get_section_range(struct module *mod,
+                                             const char *section)
+{
+       return (struct codetag_range) {
+               get_symbol(mod, "__start_", section),
+               get_symbol(mod, "__stop_", section),
+       };
+}
+
+static int codetag_module_init(struct codetag_type *cttype, struct module *mod)
+{
+       struct codetag_range range;
+       struct codetag_module *cmod;
+       int err;
+
+       range = get_section_range(mod, cttype->desc.section);
+       if (!range.start || !range.stop) {
+               pr_warn("Failed to load code tags of type %s from the module 
%s\n",
+                       cttype->desc.section,
+                       mod ? mod->name : "(built-in)");
+               return -EINVAL;
+       }
+
+       /* Ignore empty ranges */
+       if (range.start == range.stop)
+               return 0;
+
+       BUG_ON(range.start > range.stop);
+
+       cmod = kmalloc(sizeof(*cmod), GFP_KERNEL);
+       if (unlikely(!cmod))
+               return -ENOMEM;
+
+       cmod->mod = mod;
+       cmod->range = range;
+
+       down_write(&cttype->mod_lock);
+       err = idr_alloc(&cttype->mod_idr, cmod, 0, 0, GFP_KERNEL);
+       if (err >= 0)
+               cttype->count += range_size(cttype, &range);
+       up_write(&cttype->mod_lock);
+
+       if (err < 0) {
+               kfree(cmod);
+               return err;
+       }
+
+       return 0;
+}
+
+struct codetag_type *
+codetag_register_type(const struct codetag_type_desc *desc)
+{
+       struct codetag_type *cttype;
+       int err;
+
+       BUG_ON(desc->tag_size <= 0);
+
+       cttype = kzalloc(sizeof(*cttype), GFP_KERNEL);
+       if (unlikely(!cttype))
+               return ERR_PTR(-ENOMEM);
+
+       cttype->desc = *desc;
+       idr_init(&cttype->mod_idr);
+       init_rwsem(&cttype->mod_lock);
+
+       err = codetag_module_init(cttype, NULL);
+       if (unlikely(err)) {
+               kfree(cttype);
+               return ERR_PTR(err);
+       }
+
+       mutex_lock(&codetag_lock);
+       list_add_tail(&cttype->link, &codetag_types);
+       mutex_unlock(&codetag_lock);
+
+       return cttype;
+}
-- 
2.37.2.672.g94769d06f0-goog