linux-kernel - [PATCH v2 2/2] module: Add module name to modinfo

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Message-Id: <1492814127-66318-3-git-send-email-keescook@chromium.org>
Date:   Fri, 21 Apr 2017 15:35:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jessica Yu <jeyu@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Heinrich Schuchardt <xypron.glpk@....de>,
        Nicholas Piggin <npiggin@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] module: Add module name to modinfo

Accessing the mod structure (e.g. for mod->name) prior to having completed
check_modstruct_version() can result in writing garbage to the error logs
if the layout of the mod structure loaded from disk doesn't match the
running kernel's mod structure layout. This kind of mismatch will become
much more likely if a kernel is built with different randomization seed
for the struct layout randomization plugin.

Instead, add and use a new modinfo string for logging the module name.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 kernel/module.c       | 29 ++++++++++++++++++++++-------
 scripts/mod/modpost.c |  1 +
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index ed6cf2367217..29a4a77b6849 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -299,6 +299,7 @@ int unregister_module_notifier(struct notifier_block *nb)
 EXPORT_SYMBOL(unregister_module_notifier);
 
 struct load_info {
+	char *name;
 	Elf_Ehdr *hdr;
 	unsigned long len;
 	Elf_Shdr *sechdrs;
@@ -1297,12 +1298,12 @@ static int check_version(const struct load_info *info,
 	}
 
 	/* Broken toolchain. Warn once, then let it go.. */
-	pr_warn_once("%s: no symbol version for %s\n", mod->name, symname);
+	pr_warn_once("%s: no symbol version for %s\n", info->name, symname);
 	return 1;
 
 bad_version:
 	pr_warn("%s: disagrees about version of symbol %s\n",
-	       mod->name, symname);
+	       info->name, symname);
 	return 0;
 }
 
@@ -2892,9 +2893,15 @@ static int rewrite_section_headers(struct load_info *info, int flags)
 		info->index.vers = 0; /* Pretend no __versions section! */
 	else
 		info->index.vers = find_sec(info, "__versions");
+	info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
+
 	info->index.info = find_sec(info, ".modinfo");
+	if (!info->index.info)
+		info->name = "(missing .modinfo section)";
+	else
+		info->name = get_modinfo(info, "name");
 	info->sechdrs[info->index.info].sh_flags &= ~(unsigned long)SHF_ALLOC;
-	info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
+
 	return 0;
 }
 
@@ -2934,14 +2941,22 @@ static struct module *setup_load_info(struct load_info *info, int flags)
 
 	info->index.mod = find_sec(info, ".gnu.linkonce.this_module");
 	if (!info->index.mod) {
-		pr_warn("No module found in object\n");
+		pr_warn("%s: No module found in object\n",
+			info->name ?: "(missing .modinfo name field)");
 		return ERR_PTR(-ENOEXEC);
 	}
 	/* This is temporary: point mod into copy of data. */
 	mod = (void *)info->sechdrs[info->index.mod].sh_addr;
 
+	/*
+	 * If we didn't load the .modinfo 'name' field, fall back to
+	 * on-disk struct mod 'name' field.
+	 */
+	if (!info->name)
+		info->name = mod->name;
+
 	if (info->index.sym == 0) {
-		pr_warn("%s: module has no symbols (stripped?)\n", mod->name);
+		pr_warn("%s: module has no symbols (stripped?)\n", info->name);
 		return ERR_PTR(-ENOEXEC);
 	}
 
@@ -2969,7 +2984,7 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
 			return err;
 	} else if (!same_magic(modmagic, vermagic, info->index.vers)) {
 		pr_err("%s: version magic '%s' should be '%s'\n",
-		       mod->name, modmagic, vermagic);
+		       info->name, modmagic, vermagic);
 		return -ENOEXEC;
 	}
 
@@ -3249,7 +3264,7 @@ static struct module *layout_and_allocate(struct load_info *info, int flags)
 	if (IS_ERR(mod))
 		return mod;
 
-	if (blacklisted(mod->name))
+	if (blacklisted(info->name))
 		return ERR_PTR(-EPERM);
 
 	err = check_modinfo(mod, info, flags);
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 30d752a4a6a6..48397feb08fb 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2126,6 +2126,7 @@ static void add_header(struct buffer *b, struct module *mod)
 	buf_printf(b, "#include <linux/compiler.h>\n");
 	buf_printf(b, "\n");
 	buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n");
+	buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n");
 	buf_printf(b, "\n");
 	buf_printf(b, "__visible struct module __this_module\n");
 	buf_printf(b, "__attribute__((section(\".gnu.linkonce.this_module\"))) = {\n");
-- 
2.7.4