Add /sys/module/name/notes

This patch adds the /sys/module/<name>/notes/ magic directory, which has a
file for each allocated SHT_NOTE section that appears in <name>.ko.  This
is the counterpart for each module of /sys/kernel/notes for vmlinux.
Reading this delivers the contents of the module's SHT_NOTE sections.  This
lets userland easily glean any detailed information about that module's
build that was stored there at compile time (e.g.  by ld --build-id).

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 109 insertions, 0 deletions

diff --git a/include/linux/module.h b/include/linux/module.h
index 5523e10fb2f0..642f325e4917 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -343,6 +343,9 @@ struct module
 
         /* Section attributes */
         struct module_sect_attrs *sect_attrs;
+
+        /* Notes attributes */
+        struct module_notes_attrs *notes_attrs;
 #endif
 
         /* Per-cpu data. */
diff --git a/kernel/module.c b/kernel/module.c
index 35246a61a7e9..c24c3c35405a 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -20,6 +20,7 @@
 #include <linux/moduleloader.h>
 #include <linux/init.h>
 #include <linux/kallsyms.h>
+#include <linux/sysfs.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
@@ -1047,6 +1048,100 @@ static void remove_sect_attrs(struct module *mod)
         }
 }
 
+/*
+ * /sys/module/foo/notes/.section.name gives contents of SHT_NOTE sections.
+ */
+
+struct module_notes_attrs {
+        struct kobject *dir;
+        unsigned int notes;
+        struct bin_attribute attrs[0];
+};
+
+static ssize_t module_notes_read(struct kobject *kobj,
+                                 struct bin_attribute *bin_attr,
+                                 char *buf, loff_t pos, size_t count)
+{
+        /*
+         * The caller checked the pos and count against our size.
+         */
+        memcpy(buf, bin_attr->private + pos, count);
+        return count;
+}
+
+static void free_notes_attrs(struct module_notes_attrs *notes_attrs,
+                             unsigned int i)
+{
+        if (notes_attrs->dir) {
+                while (i-- > 0)
+                        sysfs_remove_bin_file(notes_attrs->dir,
+                                              &notes_attrs->attrs[i]);
+                kobject_del(notes_attrs->dir);
+        }
+        kfree(notes_attrs);
+}
+
+static void add_notes_attrs(struct module *mod, unsigned int nsect,
+                            char *secstrings, Elf_Shdr *sechdrs)
+{
+        unsigned int notes, loaded, i;
+        struct module_notes_attrs *notes_attrs;
+        struct bin_attribute *nattr;
+
+        /* Count notes sections and allocate structures.  */
+        notes = 0;
+        for (i = 0; i < nsect; i++)
+                if ((sechdrs[i].sh_flags & SHF_ALLOC) &&
+                    (sechdrs[i].sh_type == SHT_NOTE))
+                        ++notes;
+
+        if (notes == 0)
+                return;
+
+        notes_attrs = kzalloc(sizeof(*notes_attrs)
+                              + notes * sizeof(notes_attrs->attrs[0]),
+                              GFP_KERNEL);
+        if (notes_attrs == NULL)
+                return;
+
+        notes_attrs->notes = notes;
+        nattr = &notes_attrs->attrs[0];
+        for (loaded = i = 0; i < nsect; ++i) {
+                if (!(sechdrs[i].sh_flags & SHF_ALLOC))
+                        continue;
+                if (sechdrs[i].sh_type == SHT_NOTE) {
+                        nattr->attr.name = mod->sect_attrs->attrs[loaded].name;
+                        nattr->attr.mode = S_IRUGO;
+                        nattr->size = sechdrs[i].sh_size;
+                        nattr->private = (void *) sechdrs[i].sh_addr;
+                        nattr->read = module_notes_read;
+                        ++nattr;
+                }
+                ++loaded;
+        }
+
+        notes_attrs->dir = kobject_add_dir(&mod->mkobj.kobj, "notes");
+        if (!notes_attrs->dir)
+                goto out;
+
+        for (i = 0; i < notes; ++i)
+                if (sysfs_create_bin_file(notes_attrs->dir,
+                                          &notes_attrs->attrs[i]))
+                        goto out;
+
+        mod->notes_attrs = notes_attrs;
+        return;
+
+  out:
+        free_notes_attrs(notes_attrs, i);
+}
+
+static void remove_notes_attrs(struct module *mod)
+{
+        if (mod->notes_attrs)
+                free_notes_attrs(mod->notes_attrs, mod->notes_attrs->notes);
+}
+
 #else
 
 static inline void add_sect_attrs(struct module *mod, unsigned int nsect,
@@ -1057,6 +1152,15 @@ static inline void add_sect_attrs(struct module *mod, unsigned int nsect,
 static inline void remove_sect_attrs(struct module *mod)
 {
 }
+
+static inline void add_notes_attrs(struct module *mod, unsigned int nsect,
+                                   char *sectstrings, Elf_Shdr *sechdrs)
+{
+}
+
+static inline void remove_notes_attrs(struct module *mod)
+{
+}
 #endif /* CONFIG_KALLSYMS */
 
 #ifdef CONFIG_SYSFS
@@ -1191,6 +1295,7 @@ static void free_module(struct module *mod)
 {
         /* Delete from various lists */
         stop_machine_run(__unlink_module, mod, NR_CPUS);
+        remove_notes_attrs(mod);
         remove_sect_attrs(mod);
         mod_kobject_remove(mod);
 
@@ -1918,6 +2023,7 @@ static struct module *load_module(void __user *umod,
         if (err < 0)
                 goto arch_cleanup;
         add_sect_attrs(mod, hdr->e_shnum, secstrings, sechdrs);
+        add_notes_attrs(mod, hdr->e_shnum, secstrings, sechdrs);
 
         /* Size of section 0 is 0, so this works well if no unwind info. */
         mod->unwind_info = unwind_add_table(mod,