Commit caf7501a authored by Andi Kleen's avatar Andi Kleen Committed by Thomas Gleixner
Browse files

module/retpoline: Warn about missing retpoline in module 



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: default avatarAndi Kleen <ak@linux.intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: gregkh@linuxfoundation.org
Cc: torvalds@linux-foundation.org
Cc: jeyu@kernel.org
Cc: arjan@linux.intel.com
Link: https://lkml.kernel.org/r/20180125235028.31211-1-andi@firstfloor.org
parent c940a3fb

arch/x86/kernel/cpu/bugs.c

+16 −1
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <linux/init.h>

#include <linux/utsname.h>

#include <linux/cpu.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)

{
@@ -278,6 +292,7 @@ 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\n", spectre_v2_strings[spectre_v2_enabled]);

	return sprintf(buf, "%s%s\n", spectre_v2_strings[spectre_v2_enabled],

		       spectre_v2_bad_module ? " - vulnerable module loaded" : "");

}

#endif

include/linux/module.h

+9 −0
Original line number Diff line number Diff line
@@ -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)

{

kernel/module.c

+11 −0
Original line number Diff line number Diff line
@@ -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 "

scripts/mod/modpost.c

+9 −0
Original line number Diff line number Diff line
@@ -2165,6 +2165,14 @@ 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";
@@ -2506,6 +2514,7 @@ int main(int argc, char **argv) 
		err |= check_modname_len(mod);

		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);

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