warn when non-RETPOLINED module gets loaded

patches/kernel/0023-module-retpoline-Warn-about-missing-retpoline-in-mod.patch

@@ -0,0 +1,164 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Andi Kleen <[email protected]>
+Date: Thu, 25 Jan 2018 15:50:28 -0800
+Subject: [PATCH] module/retpoline: Warn about missing retpoline in module
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+There's a risk that a kernel which has full retpoline mitigations becomes
+vulnerable when a module gets loaded that hasn't been compiled with the
+right compiler or the right option.
+
+To enable detection of that mismatch at module load time, add a module info
+string "retpoline" at build time when the module was compiled with
+retpoline support. This only covers compiled C source, but assembler source
+or prebuilt object files are not checked.
+
+If a retpoline enabled kernel detects a non retpoline protected module at
+load time, print a warning and report it in the sysfs vulnerability file.
+
+[ tglx: Massaged changelog ]
+
+Signed-off-by: Andi Kleen <[email protected]>
+Signed-off-by: Thomas Gleixner <[email protected]>
+Cc: David Woodhouse <[email protected]>
+Cc: [email protected]
+Cc: [email protected]
+Cc: [email protected]
+Cc: [email protected]
+Link: https://lkml.kernel.org/r/[email protected]
+(backported from commit caf7501a1b4ec964190f31f9c3f163de252273b8)
+Conflicts:
+	arch/x86/kernel/cpu/bugs.c
+context changes
+Signed-off-by: Fabian Grünbichler <[email protected]>
+---
+ include/linux/module.h     |  9 +++++++++
+ arch/x86/kernel/cpu/bugs.c | 19 +++++++++++++++++--
+ kernel/module.c            | 11 +++++++++++
+ scripts/mod/modpost.c      |  9 +++++++++
+ 4 files changed, 46 insertions(+), 2 deletions(-)
+
+diff --git a/include/linux/module.h b/include/linux/module.h
+index e7bdd549e527..c4fdf7661f82 100644
+--- a/include/linux/module.h
++++ b/include/linux/module.h
+@@ -794,6 +794,15 @@ static inline void module_bug_finalize(const Elf_Ehdr *hdr,
+ static inline void module_bug_cleanup(struct module *mod) {}
+ #endif	/* CONFIG_GENERIC_BUG */
+ 
++#ifdef RETPOLINE
++extern bool retpoline_module_ok(bool has_retpoline);
++#else
++static inline bool retpoline_module_ok(bool has_retpoline)
++{
++	return true;
++}
++#endif
++
+ #ifdef CONFIG_MODULE_SIG
+ static inline bool module_sig_ok(struct module *module)
+ {
+diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
+index d5bafcdb4891..e623bd731a74 100644
+--- a/arch/x86/kernel/cpu/bugs.c
++++ b/arch/x86/kernel/cpu/bugs.c
+@@ -11,6 +11,7 @@
+ #include <linux/utsname.h>
+ #include <linux/cpu.h>
+ #include <linux/smp.h>
++#include <linux/module.h>
+ 
+ #include <asm/nospec-branch.h>
+ #include <asm/cmdline.h>
+@@ -93,6 +94,19 @@ static const char *spectre_v2_strings[] = {
+ #define pr_fmt(fmt)     "Spectre V2 mitigation: " fmt
+ 
+ static enum spectre_v2_mitigation spectre_v2_enabled = SPECTRE_V2_NONE;
++static bool spectre_v2_bad_module;
++
++#ifdef RETPOLINE
++bool retpoline_module_ok(bool has_retpoline)
++{
++	if (spectre_v2_enabled == SPECTRE_V2_NONE || has_retpoline)
++		return true;
++
++	pr_err("System may be vunerable to spectre v2\n");
++	spectre_v2_bad_module = true;
++	return false;
++}
++#endif
+ 
+ static void __init spec2_print_if_insecure(const char *reason)
+ {
+@@ -299,7 +313,8 @@ ssize_t cpu_show_spectre_v2(struct device *dev,
+ 	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
+ 		return sprintf(buf, "Not affected\n");
+ 
+-	return sprintf(buf, "%s%s\n", spectre_v2_strings[spectre_v2_enabled],
+-		       ibpb_inuse ? ", IBPB (Intel v4)" : "");
++	return sprintf(buf, "%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
++		       ibpb_inuse ? ", IBPB (Intel v4)" : "",
++		       spectre_v2_bad_module ? " - vulnerable module loaded" : "");
+ }
+ #endif
+diff --git a/kernel/module.c b/kernel/module.c
+index e5b878b26906..de7db074f793 100644
+--- a/kernel/module.c
++++ b/kernel/module.c
+@@ -2855,6 +2855,15 @@ static int check_modinfo_livepatch(struct module *mod, struct load_info *info)
+ }
+ #endif /* CONFIG_LIVEPATCH */
+ 
++static void check_modinfo_retpoline(struct module *mod, struct load_info *info)
++{
++	if (retpoline_module_ok(get_modinfo(info, "retpoline")))
++		return;
++
++	pr_warn("%s: loading module not compiled with retpoline compiler.\n",
++		mod->name);
++}
++
+ /* Sets info->hdr and info->len. */
+ static int copy_module_from_user(const void __user *umod, unsigned long len,
+ 				  struct load_info *info)
+@@ -3021,6 +3030,8 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
+ 		add_taint_module(mod, TAINT_OOT_MODULE, LOCKDEP_STILL_OK);
+ 	}
+ 
++	check_modinfo_retpoline(mod, info);
++
+ 	if (get_modinfo(info, "staging")) {
+ 		add_taint_module(mod, TAINT_CRAP, LOCKDEP_STILL_OK);
+ 		pr_warn("%s: module is from the staging directory, the quality "
+diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
+index 48397feb08fb..cc91f81ac33e 100644
+--- a/scripts/mod/modpost.c
++++ b/scripts/mod/modpost.c
+@@ -2147,6 +2147,14 @@ static void add_intree_flag(struct buffer *b, int is_intree)
+ 		buf_printf(b, "\nMODULE_INFO(intree, \"Y\");\n");
+ }
+ 
++/* Cannot check for assembler */
++static void add_retpoline(struct buffer *b)
++{
++	buf_printf(b, "\n#ifdef RETPOLINE\n");
++	buf_printf(b, "MODULE_INFO(retpoline, \"Y\");\n");
++	buf_printf(b, "#endif\n");
++}
++
+ static void add_staging_flag(struct buffer *b, const char *name)
+ {
+ 	static const char *staging_dir = "drivers/staging";
+@@ -2492,6 +2500,7 @@ int main(int argc, char **argv)
+ 
+ 		add_header(&buf, mod);
+ 		add_intree_flag(&buf, !external_module);
++		add_retpoline(&buf);
+ 		add_staging_flag(&buf, mod->name);
+ 		err |= add_versions(&buf, mod);
+ 		add_depends(&buf, mod, modules);
+-- 
+2.14.2
+