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module/retpoline: Warn about missing retpoline in module

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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 <ak@linux.intel.com>
Signed-off-by: Thomas 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
This commit is contained in:
Andi Kleen 2018-01-25 15:50:28 -08:00 committed by Thomas Gleixner
parent c940a3fb1e
commit caf7501a1b
4 changed files with 45 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
arch/x86/kernel/cpu/bugs.c
View File

@ -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

9
include/linux/module.h
View File

@ -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)
{

11
kernel/module.c
View File

@ -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 "

9
scripts/mod/modpost.c
View File

@ -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);