linux-kernel - [RFC PATCH v2 14/19] dyndbg+module: expose ddebug

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Date:   Fri, 25 Dec 2020 13:19:39 -0700
From:   Jim Cromie <jim.cromie@...il.com>
To:     jbaron@...mai.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org
Cc:     Jim Cromie <jim.cromie@...il.com>
Subject: [RFC PATCH v2 14/19] dyndbg+module: expose ddebug_callsites to modules

In order to drop the pointer connecting _ddebug records to _callsites,
we need to elevate the latter; we need to track it in (internal)
ddebug_tables, and set it in ddebug_add_module.  That last part
exposes it by interface to module.c, so we add a field to load_info,
and adjust load_module to initialize it from the elf section.

Its possible that this closes a hole created when __dyndbg_callsites
section was added, and wasnt handled by module load-info.  I never saw
any misbehavior loading i915.ko into a vm, but still..

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/linux/dynamic_debug.h |  4 ++--
 kernel/module-internal.h      |  1 +
 kernel/module.c               |  9 ++++++---
 lib/dynamic_debug.c           | 12 ++++++++----
 4 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 49fa1390d1f8..0fcbe96736f3 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -70,8 +70,8 @@ struct _ddebug {
 /* exported for module authors to exercise >control */
 int dynamic_debug_exec_queries(const char *query, const char *modname);
 
-int ddebug_add_module(struct _ddebug *tab, unsigned int n,
-				const char *modname);
+int ddebug_add_module(struct _ddebug *tab, struct _ddebug_callsite *sites,
+		      unsigned int n, const char *modname);
 extern int ddebug_remove_module(const char *mod_name);
 extern __printf(2, 3)
 void __dynamic_pr_debug(struct _ddebug *descriptor, const char *fmt, ...);
diff --git a/kernel/module-internal.h b/kernel/module-internal.h
index 33783abc377b..920b085d2a1b 100644
--- a/kernel/module-internal.h
+++ b/kernel/module-internal.h
@@ -18,6 +18,7 @@ struct load_info {
 	char *secstrings, *strtab;
 	unsigned long symoffs, stroffs, init_typeoffs, core_typeoffs;
 	struct _ddebug *debug;
+	struct _ddebug_callsite *sites;
 	unsigned int num_debug;
 	bool sig_ok;
 #ifdef CONFIG_KALLSYMS
diff --git a/kernel/module.c b/kernel/module.c
index a4fa44a652a7..876765bc666a 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2820,11 +2820,12 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 }
 #endif /* CONFIG_KALLSYMS */
 
-static void dynamic_debug_setup(struct module *mod, struct _ddebug *debug, unsigned int num)
+static void dynamic_debug_setup(struct module *mod, struct _ddebug *debug,
+				struct _ddebug_callsite *sites, unsigned int num)
 {
 	if (!debug)
 		return;
-	ddebug_add_module(debug, num, mod->name);
+	ddebug_add_module(debug, sites, num, mod->name);
 }
 
 static void dynamic_debug_remove(struct module *mod, struct _ddebug *debug)
@@ -3299,6 +3300,8 @@ static int find_module_sections(struct module *mod, struct load_info *info)
 
 	info->debug = section_objs(info, "__dyndbg",
 				   sizeof(*info->debug), &info->num_debug);
+	info->sites = section_objs(info, "__dyndbg_callsites",
+				   sizeof(*info->sites), &info->num_debug);
 
 	return 0;
 }
@@ -3937,7 +3940,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
 		goto free_arch_cleanup;
 	}
 
-	dynamic_debug_setup(mod, info->debug, info->num_debug);
+	dynamic_debug_setup(mod, info->debug, info->sites, info->num_debug);
 
 	/* Ftrace init must be called in the MODULE_STATE_UNFORMED state */
 	ftrace_module_init(mod);
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index c1a113460637..8ad9be28f38e 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -49,6 +49,7 @@ struct ddebug_table {
 	const char *mod_name;
 	unsigned int num_ddebugs;
 	struct _ddebug *ddebugs;
+	struct _ddebug_callsite *sites;
 };
 
 struct ddebug_query {
@@ -1014,8 +1015,8 @@ static const struct proc_ops proc_fops = {
  * Allocate a new ddebug_table for the given module
  * and add it to the global list.
  */
-int ddebug_add_module(struct _ddebug *tab, unsigned int n,
-			     const char *name)
+int ddebug_add_module(struct _ddebug *tab, struct _ddebug_callsite *sites,
+		      unsigned int n, const char *name)
 {
 	struct ddebug_table *dt;
 
@@ -1033,6 +1034,7 @@ int ddebug_add_module(struct _ddebug *tab, unsigned int n,
 	dt->mod_name = name;
 	dt->num_ddebugs = n;
 	dt->ddebugs = tab;
+	dt->sites = sites;
 
 	mutex_lock(&ddebug_lock);
 	list_add(&dt->link, &ddebug_tables);
@@ -1182,7 +1184,9 @@ static int __init dynamic_debug_init(void)
 
 		if (strcmp(modname, iter->site->modname)) {
 			modct++;
-			ret = ddebug_add_module(iter_mod_start, n, modname);
+
+			ret = ddebug_add_module(iter_mod_start, site_mod_start,
+						n, modname);
 			if (ret)
 				goto out_err;
 			n = 0;
@@ -1192,7 +1196,7 @@ static int __init dynamic_debug_init(void)
 		}
 		n++;
 	}
-	ret = ddebug_add_module(iter_mod_start, n, modname);
+	ret = ddebug_add_module(iter_mod_start, site_mod_start, n, modname);
 	if (ret)
 		goto out_err;
 
-- 
2.29.2